centrifugal pumps

Centrifugal pumps: characteristics and functioning

Centrifugal pumps are used in a very wide range of industries, from chemical-petrochemical to textile to water treatment, electronic, etc.
If you are looking for accurate and specific information regarding centrifugal pumps, you are in the right place! In the following paragraphs, in fact, we are going to explain their characteristics and how they work.

Centrifugal pumps: classification

Based on the position of the drive shaft that moves the impeller, there are two types of centrifugal pumps

  • horizontal pumps 
  • vertical pumps: suitable for applications where installation of the pump semi-submersed in the liquid is required (tanks, reservoirs, sumps etc.)

Horizontal centrifugal pumps can be installed: 

  • above the fluid level: in this case, the pump has to be self-priming
  • below the fluid level: the pump is installed below the liquid level so it is flooded

Centrifugal pumps are composed of an impeller, assembled on the motor shaft, which rotates inside the pump head. The liquid enters in the axial direction but different types of pumps have different outflow directions:

  • Radial flow pumps (most common)
  • Axial flow pumps
  • Mixed flow pumps

Centrifugal pumps: components

The main components are:

  • the pump head (or pump casing)
  • the impeller, which is connected to the motor shaft. You can choose between different types of impellers for centrifugal pumps: open, which is used with liquids with a higher concentration of impurities; closed, when there is a smaller percentage of suspended solids; semi-open etc. 
  • the shaft
  • the motor
  • Sealing system to prevent liquid leakage between the pump head and the shaft

There are different types of sealing systems, such as: 

  • mechanical seal pumps, in which the pump shaft, connected to the impeller, exits to the outside to be connected to the motor, and a mechanical seal is installed to ensure sealing
  • mag drive centrifugal pumps in which the external magnet is assembled directly on the motor shaft and it transmits motion to the impeller by means of an internal magnet through magnetic force. In this case, the shaft does not pass to the outside of the pump. 

The external magnet placed on the drive shaft transmits the motion to the internal magnet connected to the impeller which rotates and moves the fluid through the pump. So the containment rear casing contains the internal magnet mentioned above and it ensures a hermetic seal on the hydraulic part of the pump, keeping it separated from the motor.

The figure below shows the main components of these pumps:

Centrifugal pumps: functioning

How does a centrifugal pump work? Operating curves and graphs can be used to describe their performance and area of work.
For a centrifugal pump, the performance curves can be seen in graph 4.1 while graph 4.2 shows the case of a positive displacement pump:

graph 4.1pumps curves positive displacement pump curves graph 4.2

The top graph in both figures describes the head variation given by the pumps as the flow rate changes. The best performance is recorded by working centrally, both on the x-axis and y-axis. So between 2 and 2.5 m3/h and between a head of 4 and 5 m. 

For the proper functioning of a centrifugal pump plant, it is necessary to verify that the NPSH available in the plant is higher than the NPSH required by the pump.

We will not expand on the explanation of NPSH here but you can refer to the following link: https://www.gemmecotti.com/npsh-a-brief-explanation/

GemmeCotti centrifugal pumps

GemmeCotti can supply four different models of mag drive pumps and one model of mechanical seal pumps: 


  • thermoplastic pumps made in PP or PVDF
  • capacity up to 130 m3/h
  • head up to 48 mlc
  • HTM : injection molded parts – HCM: casing machined from a block

HTM mag drive centrifugal pump           HCM mag drive centrifugal pump


  • thermoplastic pumps made in PP or PVDF
  • capacity up to  25 m3/h
  • head up to 22 mlc
  • injection molded parts
  • self-priming up to 6 m

HTM-SP self-priming mag drive pumps


  • thermoplastic pumps made in AISI 316
  • capacity up to 32 m3/h
  • head up to 24 mlc

HTM SS316 mag drive centrifugal pump


  • thermoplastic pumps made in PP or PVDF
  • Flow up to 130 m3/h
  • Head up to 48 mlc

HCO mechanical seal pump

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plastic pumps

Plastic pumps: characteristics and advantages

GemmeCotti plastic pumps for acids and dangerous liquids

GemmeCotti has been producing pumps for acids and dangerous liquids for over 30 years in special materials: plastic pumps are mainly made of PP (polypropylene) or PVDF and stainless steel pumps are mainly made of AISI 316. The use of these materials ensures compatibility with a wide range of liquids such as acids, bases, oils, alkalis, refrigerants and fuels. 

In this article, we will focus on the plastic materials used for the complete range of our chemical pumps. We will analyze their main features and discover why plastic pumps are especially suitable for pumping corrosive and dangerous liquids such as sulfuric acid, sodium hydroxide, hydrochloric acid, acetone, cleaners, petrol, diesel, phosphoric acid and seawater.

Most of the PP and PVDF injected plastic parts used in GemmeCotti pumps are manufactured by Gemme Plast, a part of the GemmeCotti group, which specializes in the injection molding of plastic materials

Features of the plastic materials 

Our pumps are often used with fluids that can be corrosive and very aggressive, so it’s very important to use highly resistant and compatible plastic pumps. The pumps made of plastic materials are: 

Polypropylene [PP] pumps

PP (Polypropylene) is the main plastic material we use for our pumps. It is one of the most common polymers and, historically, one of the first to be used in industry.
Polypropylene was discovered in 1954 by Italian chemical engineer Giulio Natta, following the work of Karl Ziegler in Germany. Their innovative studies on stereospecific polymerization, which led to the discovery of crystalline polypropylene, earned them the Nobel Prize in Chemistry in 1963.
PP is highly resistant and therefore can be used with many fluids like caustic soda (or sodium hydroxide) and acid liquids. Polypropylene is reinforced with other materials like glass fiber and talc to make it more mechanically resistant and to ensure a higher resistance to pressure.
Polypropylene is perfect for obtaining injection molded parts, and the pumps made of this material can safely withstand fluid temperatures of about 60-70°C.

Plastic pumps in PVDF 

The second most important material we use for GemmeCotti plastic pumps is PVDF, which is a fluoropolymer, i.e., a technopolymer with advanced properties. Its composition makes it chemically inert to most chemicals. Since this kind of plastic is difficult to synthesize and is used in more limited and specialized sectors, it costs more than PP. However, It is significantly more resistant to high temperatures compared to polypropylene and it can be used at higher temperatures, up to 90°C.
This material too is reinforced to increase its mechanical resistance

How to choose the most suitable pump material

In order to decide whether PP, PVDF or stainless steel AISI 316 is the most suitable material you must:

  • first, know the liquid that has to be pumped, which is in contact with the pump and verify its compatibility. You can use the GemmeCotti chemical compatibility chart available at this link;
  • and then know the temperatures of the liquids to be pumped. Polypropylene is the most suitable plastic material for liquids with maximum temperatures of 60-70°C, while PVDF is preferred for temperatures up to 90 ºC.  When the temperature of the liquid exceeds 90 ºC, you can check its compatibility with stainless steel AISI 316, a material that can work with even higher temperatures.

Plastic injection molding

The GemmeCotti group includes the sister company Gemme Plast, which makes injection molded parts. Plastic parts are injection molded, a production technique widely used for the processing of most thermoplastic polymers. We produce plastic parts that are used for the production of GemmeCotti pumps and that is why we are able to control the quality of our production and guarantee our customers fast delivery with significant savings.
Gemme Plast has a range of different tonnage presses, which make it possible to inject plastic parts of various sizes according to need. So we can offer pumps with a very wide range of performance, varying from 0.5m3/h to 150m3/h.

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The emission of gasses in the atmosphere is regulated by specific national and international laws that must be respected by all industries. The term “air treatment” refers to systems and techniques used by the industries to keep the air quality and the level of pollution under control.

Scrubbers are the easiest and most efficient systems for purifying the air by removing particulates and/or gasses.

There are several types of scrubbers which are used in different industrial sectors.



Scrubbers are generally used to:

  • wash fumes (e.g. emitted by boilers or furnaces) with soda or other liquids, in order to remove hydrogen sulfide, hydrochloric acid, hydrocarbons and sulfur dioxide.
  • depurate gasses (e.g. washing synthetic gasses with monoethanolamine in order to remove CO2).

Scrubbers are generally used by:

  • petrochemical industries
  • chemical and pharmaceutical industries
  • galvanic industries
  • packaging industries
  • food industries
  • cellulose industries



The polluted air is directed inside a chamber where it comes into contact with the washing liquid which transfers the pollutants from the air to the water. The purified air is released into the atmosphere while the polluting particles become an integral part of the washing liquid, which is then collected in a tank.

During this process, the polluted air goes from the bottom to the top while the washing liquid is pushed up by the use of centrifugal pumps and then it goes from the top to the bottom through the scrubber. The washing liquid collected in the tank is then recirculated by means of horizontal centrifugal pumps installed on the ground or through vertical pumps installed directly inside the tank. The pump continues to recirculate the same liquid which, after the transfer through the scrubber, returns to the tank.


Additives inside the washing liquid are often hazardous chemical agents. For this reason it is necessary to use anti-corrosion pumps.

The pump used in this process can be installed next to the tank or vertically immersed in it.

In both cases, GemmeCotti offers suitable solutions:

Horizontal centrifugal pumps:
– series HTM PP/PVDF (magnetic driven)
– series HCO (mechanical sealed)
are the best solution for the installation next to the tank.

Vertical centrifugal pumps:
– series HV (monoblock)
– series HVL (with bracket)
are the ideal solution for installation with the pump immersed in the tank.

All these centrifugal pumps are made of thermoplastic materials PP or PVDF, which ensure a great chemical resistance to the chemical agents used in this application.



Mag drive pumps HTM PP/PVDF have a sealless design that is particularly suitable to pump corrosive and dangerous liquids; the magnetic design together with the usage of anticorrosive thermoplastic materials, ensures the high chemical resistance and the absence of leakage and emissions.

GemmeCotti HTM scrubbers

Technical data:

– Capacity up to 130 m3/h

– Head up to 48 mlc

Discover more


Mechanical seal centrifugal pumps HCO are the best solution when the liquid has solids in suspension: their design with open impeller permits to transfer dirty liquids (non-abrasive solids – max. 5% – dimension max. 3 mm).

Technical data:GemmeCotti HCO scrubbers

– Capacity up to 60 m3/h
– Head up to 38 mlc

Discover more


Vertical centrifugal pumps are suitable for installations with the pump immersed directly in the tank.


Pumps series HV are available with different column lengths from 500 mm to 1000 mm.

Technical data:

– Capacity up to 40m3/h
– Head up to 22 mlc

Discover more


Pump series HVL are available with different column lengths from 500 mm to 2000mm.

Technical data:                                                                    GemmeC

– Capacity up to 57m3/h
– Head up to 39 mlc

Discover more




Contact our commercial department, we will find together an interesting solution for your application: info@gemmecotti.com




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HTM SP mag drive centrifugal pump self-priming

We are extending our product line: our new pump is ready!

We are happy to announce our new mag drive centrifugal pump self-priming HTM SP!

GemmeCotti HTM SP pumps combine the typical features of our mag drive centrifugal pumps with the self-priming capability. These pumps can prime up to 6 meters at sea level.



HTM SP pumps are made of Polypropylene (PP), a thermoplastic material that ensures the best resistance to most chemicals.

All the internal plastic parts are obtained through the injection moulding process that we directly manage in our sister company Gemme Plast.


The new magnetic centrifugal pump self-priming HTM SP can reach a capacity of 25 m3/h and a head of 22 m.

The suction connection of this pump can be customized in 3 welded configurations according to your needs (frontal, on the right and on the left).

HTM SP curves


Mag drive pumps have a special sealless design that is suitable for pumping corrosive and dangerous liquids thanks to the high chemical resistance and to the absence of leakage and emissions. The structure is really simple and it requires very little maintenance with consequent savings in terms of repairing, spare parts and machine downtime costs during the pump life.

In magnetic pumps, there is an external magnet which is connected to the shaft of the electric motor.
The synchronous motion is transmitted from the motor to the rotor (consisting of the internal magnet and the impeller) through the external magnet. The two magnets never come into contact, they are moved by the magnetic field only. The impeller connected to the internal magnet spins around a static shaft and the liquid moves through the pump. The whole hydraulic part is hermetically sealed: in the space between the magnets there is a rear casing which closes on the pump head and prevents the pumped liquid from coming out of the pump.

The pumped liquid must be clean, without solids in suspension (max. quantity of solids: max 2% – max 1mm).

Read more about the magnetic system


• Materials available: PP or PVDF*;
• Materials in contact with the liquid: Pump housing: PP; Impeller: PP or PVDF;
O-ring: EPDM (standard for PP pumps) / VITON
(standard for PVDF pumps); Static shaft: Al2O3 99.7%; Bearing: PTFEC.
• Capacity up to 25 m3/h.
• Head up to 22 m.
• Max temperature: PP: 70° C – PVDF: 90° C.
• Max viscosity: 200 cSt.HTM SP connections
• Pressure rating: PN6 at 20° C.
• Self-priming up to 6m at sea level.
• Suction connection available in 3 welded configurations
(frontal, on the right and on the left).
*Pump housing only available in PP.

• Gas threaded In and Out connections.
• Direct starting motor.

• Baseplate.


   HTM SP is now available!

                       Contact our office at info@gemmecotti.com for any further information.        

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Since 1992 GemmeCotti has been manufacturing several types of high quality chemical pumps suitable for most industrial applications.

Everyday we employ all our experience to improve the existing products and to design new projects in order to satisfy our customers’ needs. We live in the present and we design the pumps of the future without forgetting where we started.

The magnetic drive centrifugal pump HTM PP/PVDF was our first product, the one which made us experts in the field of the pumping solutions.

HTM 10 mag drive centrifugal pump

Over the years we developed the series that now includes 9 sizes: HTM 4, HTM 6, HTM 10, HTM 15, HTM 31, HTM 40, HTM 50, HTM 80, HTM 100. Each size is available in two thermoplastic materials: PP (polypropylene) and PVDF.

The HTM are high-quality pumps, extremely reliable and versatile, and they are still our bestsellers.

Which are the 7 strong points of these mag drive centrifugal pumps?


The HTM pumps are manufactured in thermoplastic materials, PP or PVDF. These anti-corrosion materials are compatible with the great majority of the acids, chemicals and dangerous liquids.

Check the chemical compatibility chart


The plastic parts of our HTM are manufactured by Gemme Plast, another company in the GemmeCotti group, which is specialized in the injection moulding of plastic. Thanks to this cooperation, we can check all the raw materials used and we have total control over the moulding process.


Advantages of the magnetic drive system:

  • no mechanical seal
  • no leakage or emissions
  • no waste of liquidsHTM magnetic drive system
  • environmental sustainability
  • reliability and safety
  • low maintenance and consequent long term savings
  • no need for a pump-motor alignment

Please note that the liquid must be clean and without solids in suspension (acceptable quantity and dimensions of the solids: max 2% – max 1mm).

Discover more about the mag drive advantages


Unlike most centrifugal pumps on the market, the pump head of the HTM is secured to the bracket with 8 bolts. This feature allows the safe fastening of the pump head, ensuring the static seal and avoiding the deformation of the pump head due to the pressure.


The wide dimensions of the frontal bearings ensure the high resistance to the axial thrusts.

6.STATIC SHAFTHTM magnet and shaft

The static shaft of the mag drive centrifugal pumps HTM is made of alumina (Al2O3), an extremely robust ceramic material that ensures great stability and resistance to most hazardous liquids.


The HTM pumps series are equipped with a high magnetic coupling created with magnets made of NdFeB. Thanks to this particular feature, the internal and external magnets won’t detach from each other while the pump is operating.



    Check the technical data of our HTM




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GemmeCotti supplies industrial pumps suitable to unload railroad tank cars and tanker trucks containing acids and toxic chemicals.


We offer three possible solutions for this application:

  • installation of one pump for each single tank
  • installation of the pump directly aboard the vehicle (GemmeCotti series HTM or series HCO)
  • use of the portable pump H-IBC (GemmeCotti series HTM 10)


The right pumping solution for unloading and transferring dangerous liquids from vehicles (trucks or railroad tank cars) is selected according to the chemical compatibility and the requested performances.

GemmeCotti pumps are the best choice to transfer dangerous or hazardous goods, i.e. all the substances which, due to their peculiar properties, could be harmful for the environment or the people involved.

These liquids are classified according to their characteristics and degree of danger. In Europe, the transportation of toxic chemicals is regulated by specific laws:

  • ADR: agreement concerning the international transport of dangerous goods by road
  • RID: international carriage of dangerous goods by railrailroad-tank-cars
  • ADN: carriage of dangerous goods by inland waterways

GemmeCotti is proud to offer pumping solutions for the safe handling of chemicals: we supply chemical pumps suitable for the safe offloading of the great majority of dangerous or hazardous goods.

Fluids generally involved in this application:

  • ammonia
  • sulphuric acid
  • nitric acid
  • hydrochloric acid
  • sodium hydroxide (caustic soda)
  • hydrogen peroxide

…and many more!

Check the chemical compatibility guide


The GemmeCotti pumps installed on means of transport and involved in the unloading process, permit to direct and move the fluids in total safety, ensuring quick execution.

For this application, GemmeCotti recommends:

  • magnetic drive centrifugal pumps series HTM PP/PVDF
  • mechanical seal centrifugal pumps series HCO

The design of these two types of centrifugal pumps, permits the safe installation both on land and aboard the vehicle, ensuring a constant flow without the risk of leakage or emissions.

Magnetic pumps series HTM PP/PVDF

Mechanical seal pumps series HCO

Another practical and effective solution is the use of the GemmeCotti portable pump series H-IBC.


GemmeCotti H-IBC has been designed as a safe and reliable mobile pump specifically for the safe unloading of IBC containers. The unit consists of a magnetic centrifugal pump HTM 10 mounted in a robust carry case, conceived to be easy to move. Thanks to its fast connections, H-IBC is a really flexible solution: the pump could be easily removed from the IBC container and placed in another one according to the requirements. This quick and efficient unit is suitable for several applications. Moreover, the pump is equipped with an electric panel and a start and stop switch for easy, quick and safe use.

Upon request, H-IBC pumps can be supplied in a premium version with wheels, for easier movement and transportation.view-h-ibc

Learn more about our portable pumps H-IBC series


To prevent damages to the pumps due to the lack of liquid, GemmeCotti supplies the dry running protection device. This device is particularly recommended during the operations of tanker unloading and for all the applications in which there is the risk of liquid shortage.

Thanks to the adjustable threshold and timer, it is possible to set up the minimum power and operation time of the device. If the power is lower than the set value, the pump will automatically stop.

Main features of the dry running protection device:

Dispositivo contro la marcia a secco - dry running protection device


Multirange 15-35A

2 set points MAX / min

Also for motors with INVERTER


More information about the device 


It is fundamental to choose the right pump model when dealing with acids or corrosive liquids. For theGemmeCotti HTM e HCO chemical pumps operations of tanker unloading, GemmeCotti suggests the use of mechanical seal centrifugal pumps or magnetic centrifugal pumps. The type of pump is selected according to the liquid to be pumped and to the requested working point.


Mag drive pumps have a sealless design that is particularly suitable to pump corrosive and dangerous liquids; the magnetic design together with the usage of anticorrosive materials, guarantees the high chemical resistance and the absence of leakage and emissions.

Moreover, the structure of magnetic drive pumps is really simple and requires very little maintenance with a consequent saving in terms of repairs and spare parts expenses during the pump life. The external magnet placed on the drive shaft transmits the motion to the internal magnet connected to the impeller, which rotates and moves the fluids through the pump.


Mechanical seal centrifugal pumps are the best solution when the liquid has solids in suspension: their design with open impeller permits to transfer dirty liquids and fluids with high viscosity.

The seal of these pumps is composed of a static ring and a rotating ring placed on the pump shaft, which is directly coupled to the motor shaft. When the pump is working, the two rings’ surfaces slide together and the lubrication of the parts is granted by the pumped liquid.


GemmeCotti supplies pumps for chemicals suitable for the offloading process of tanker trucks, petrol tankers and railroad tank cars. Our industrial pumps allow you to unload the fluids with the maximum efficiency, ensuring safety, reliability and saving in terms of repairs and spare parts expenses.

Upon request, GemmeCotti pumps can be supplied with single phase motors and in ATEX version for potentially explosive areas.


Contact us: info@gemmecotti.com


Our sales department is available from Monday to Friday, from 8.30 to 12.30 and from 12.30 to 14.00, to select the best chemical pump for your needs.

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The fish tanks of big aquariums allow the public to admire many fascinating underwater creatures. Through hundreds of windows the enchanted visitors look at the wide variety of plant and animal species which populate lakes, rivers and oceans of the planet.

Aquarium pumps

The invisible and complex pumping system of big aquariums permits the survival of aquatic species in freshwater and seawater inside the exhibition tanks. The circulation and filtration of the water is possible thanks to the pumps which direct the liquid through the filter before returning it to the tanks.

The pumping system must guarantee the quality of the water by maintaining its main chemical and physical properties in order to recreate the natural habitat of the aquatic flora and fauna.

The pumps used in these giant freshwater and saltwater aquariums must be corrosion resistant and able to pump large amounts of liquid. Moreover the pumps must be silent to avoid the risk of creating a stressful situation that could alter the normal fish behaviour.



Pumps made of thermoplastic materials are recommended for large systems pumping saltwater or freshwater.

The thermoplastic materials used in the manufacture of GemmeCotti pumps are solid and lightweight and they don’t absorb water. Certainly, the best material for the construction of saltwater pumps is polypropylene (PP), a thermoplastic polymer with a good thermal, mechanical and abrasive resistance.

The use of this anti corrosion material, instead of the installation of pumps in metallic materials, avoids the risk of dispersion of metallic particles, which could harm the health of the sea fauna.


Centrifugal pumps are the best choice for freshwater and seawater aquariums.

A centrifugal pump is made of a movable part called the impeller that forces the liquid under pressure in a desired direction.

GemmeCotti HTM 10 PP centrifugal pump


Centrifugal pumps can be designed with a particular system called magnetic drive.

Mag drive pumps have a sealless design that is particularly suitable to pump corrosive and dangerous liquids; the magnetic design together with the usage of anticorrosive thermoplastic materials, guarantees the high chemical resistance and the absence of leakage and emissions. Thanks to the total absence of emissions and leakage, the plant will always be clean; this feature coupled with the reduced maintenance required by GemmeCotti pumps, helps in keeping the plant efficient, secure and reliable.

The structure of magnetic drive pumps is really simple and requires very little maintenance with a consequent saving in terms of repairs and spare parts expenses during the pump life.

The use of mag drive centrifugal pumps in thermoplastic materials, such as GemmeCotti pumps series HTM PP/PVDF, is the best solution for working with fresh water and sea water. In particular, the smallest models of this series (HTM 4, HTM 6, HTM 10) are particularly recommended for the pumping system of big aquariums.


Check the technical data and download the complete catalogue!


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GemmeCotti supplies air-operated double diaphragm pumps suitable to transfer aggressive liquids with high viscosity and solids in suspension.

HAOD air-operated double diaphragm pumps

The main feature of HAOD pumps is their versatility: these volumetric self-priming pumps are suitable for applications in chemical and pharmaceutical industries and in water treatment plants. Moreover HAOD pumps are commonly used in dosing systems and they are usable for trucks or barrels.


HAOD pneumatic pumps installation


HAOD assure high pressures and high heads in addition to the compatibility with a wide selection of liquids. HAOD pumps are built with an anti-stalling pneumatic circuit which ensures the highest possible level of security and efficiency and doesn’t require lubricated air: the ecological design guarantees a reduction in the air consumption.
Moreover, HAOD are fast and easy to assemble without the use of special tools.

HAOD pneumatic pumps are available in several materials and dimensions: diaphragms are made of PTFE while the pump body can be manufactured in thermoplastic materials (PP or PVDF) or metallic materials (stainless steel AISI 316).

Air-operated double diaphragm pumps are available in ATEX version for potentially explosive atmosphere classified zone 2 II3G.



• Available in PP, PVDF and AISI316;
• Max. Temperature:
PP: 60° C – PVDF: 95° C – AISI 316: 95°;
• Adjustable capacity and head;
• Adjustable speed without pressure loss.

• Pulsation damper.



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GemmeCotti supplies ATEX pumps for potentially explosive atmospheres. Our EM pumps are suitable to be used in ZONE 1 II2G and ZONE 2 II3G classified areas. All our pumps comply with the technical and safety requirements of ATEX Directive 2014/34/EU

The Directive states that the manufacturers of equipment intended for use in potentially explosive atmospheres shall draw up a written declaration of conformity of these products.


The term “ZONE 1” indicates an area where an explosive atmosphere consisting of a mixture of air or flammable substances (gas, vapour or mist) is likely to occur in normal operation occasionally.

The term “ZONE 2” indicates an area where an explosive atmosphere consisting of a mixture of air and flammable substances (gas, vapour or mist) is not likely to occur in normal operation. If it does occur, it will persist for a short period only.


GemmeCotti ATEX pumps for potentially explosive atmospheres EM series includes 3 metallic pumps (AISI 316) and 5 plastic pumps (PP/PVDF).

ATEX PUMPS made of stainless steel AISI 316 suitable for ATEX ZONE 1 II2G and ZONE 2 II3G:

EM-C Atex centrifugal mag drive pumps:
Max flow 32 m3/h, max head 24 mlc
EM-P Atex rotary vane mag drive pumps:
Max Flow 2100 l/h, max head 13 bar
EM-T Atex turbine mag drive pumps:
Max Flow 7 m3/h, max head 78 mlc

GemmeCotti ATEX pumps in AISI 316

ATEX PUMPS made of plastic materials PP/PVDF suitable for ATEX ZONE 2 II3G:

EM-C PP-PVDF Atex centrifugal mag drive pumps:
Flow up to 130 m3/h, head up to 48 mlc
EM-T PP-PVDF Atex turbine mag drive pumps:
Max capacity: 9 m3/h, max head: 50 mlc
EM-P PP-PVDF Atex vane mag drive pumps:
Max flow: 1000 l/h, max pressure 5 bar
EM-T SP Atex turbine self-priming pumps:
Max flow: 6 m3/h, max head 24 mlc
EM-CO Atex mechanical seal pump:
Flow up to 58 m3/h, head up to 38 mlc

GemmeCotti ATEX pumps in PP PVDF


  • Acids and bases
  • Corrosive, toxic and dangerous liquids
  • Hydrocarbons, pyrophorics and other flammables
  • Heat transfer oils
  • Refrigerants and cryogenics
  • Radioactive liquids

Our ATEX pumps are suitable for various applications and they are supplied with the ATEX certificate for ATEX ZONE 1 and 2.

You should specify the ATEX zone in your enquiry, our sales office will select the right pump according to your requirements.

All the pumps include the required protective systems.

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NPSH: a very brief explanation

NPSH (net positive suction head) is one of the main parameters to be considered when selecting a pump. But what are we referring to when we talk about NPSH? And why is it so important?
First of all, we have to distinguish two different values of NPSH: the NPSH available and the NPSH required.


The NPSH available, normally shortened as NPSHa, is a value calculated by the plant engineer. It could be roughly defined as the result of the absolute pressure of a fluid at the inlet of a pump minus the vapour pressure of the liquid. It is usually expressed in meters.


The NPSH required (NPSHr) is a value that is given by the pump supplier and describes the energy losses that often occur inside the pumps when the liquid enters through the impeller eye of the pump. The value is expressed as a head of fluid (usually in meters). This is a requirement of the pump and it depends on different factors: the design and dimensions of the impeller, the speed of the pump,
the speed of the flow rate, and so on.


As we said, NPSH is fundamental in selecting and sizing a pump. Indeed, NPSHa has to be higher than NPSHr for the pump to work properly. If not, cavitation could occur, reducing the performance of the pump and, in many cases, seriously damaging it.NPSH scheme

Cavitation is a physical phenomenon that can happen in a pump. It causes the formation of little gas bubbles inside the liquid when the system pressure goes below the vapour pressure of the fluid. These bubbles instantly collapse when the fluid is inside the impeller, beyond the impeller inlet, due to the increasing of the pressure. The collapse produces microjets with a very high impact on the impeller, which gets significantly damaged. Because the impeller is unbalanced, vibrations and all the related issues can arise: seal failure and bearings serious damaging.


For this reason, the plant engineer has to keep NPSH values in mind at all times. The pump performance curve usually includes a NPSHr graph so that the engineer can check the operating conditions. As a matter of fact, it’s necessary for the NPSHr of the pump to be lower than NPSHa in the plant. The safety margin between NPSHr and NPSHa has to be minimum of 0.5 meters.
Only if this ratio is respected the pump will work properly and cavitation will be avoided.

npsh curve 1

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Pump selection: all the parameters

As pump manufacturers, we daily face with a lot of inquiries that are often not complete because of the lack of data that are essential to let us quote the correct pump solution. In order to help our customer to get their way out of the jungle of the parameters, we have defined a table of the main variables that should be considered during the pump selection. This article would like to be a light vademecum to simplify the communication requesting for a quotation.

Variables of the pump selection

The following table includes the indispensable variables that our technicians have to know during the selection. We strongly recommend our customers to communicate the following data so that we can proceed with the selection.

pump selection

Thanks to these references, our technical department will be able to select the best solution for every inquiry.

Moreover, once the selection is done, our technical department will provide the customers with some helpful derived parameters that are necessary for the plants.

Parameters confirmed by the pump technicians

Indeed, after the selection, our technicians, first of all, confirm the actual head and flow that pump can reach and the diameter of the impeller. Then they give the customers the data shown in the table below. This information let our customer be able to technically evaluate our proposal according to the construction features of the plant.

after the pump selection


Is it more clear now? Should you need any further information, please contact us at info@gemmecotti.com. We will be glad to dissipate all your doubts.

Don’t forget to save this post in your bookmarks, in order to easily recover it! And to select the right material for the pump, take a look also at our chemical compatibility guide.




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AODD pumps: 4 reasons to choose diaphragm pumps


AODD pumpsThe AODD pumps, Air Operated Double Diaphragm pumps, appeared in the pump market for the first time about sixty years ago. Thanks to the constant technological improvement, they have managed to set themselves as the best choice for pumping high-viscosity fluids.

There are four reasons why you should prefer a double diaphragm pump as our HAOD pumps for your plant. Here they are:


    The AODD pumps find application in a wide range of installations, thanks to their versatility and to their features. For example: the ability to self-prime, the possibility to run dry, the potential to be submersible, and the possibility to pump high-viscosity fluids. Moreover they are available in different materials in order to overcome any problems of fluid compatibility.


    The design and the ease of use of the AODD pumps are among the reasons they are so appreciated in the chemical pumps market. Indeed they are often described as “plug-in-and-play” or “set-and-forget” pumps, because once installed and connected to a compressed airline they can work for themselves in full autonomy. They can be provided in a multiplicity of dimensions, easily meeting every customers’ needs.


    Thanks to its closed design, the usage of compressed air as the only power source, and its stall-prevention pneumatic system, AODD pumps are one of the safest pumping system for hazardous liquids, together with the mag-drive pumps. Moreover the ecological design of AODD pumps allows them to realize up to 60% saving in air consumption. Thanks to this saving, their impact on environment decreases significantly. Less air consumption means indeed the possibility to use smaller air compressor, with consequent energy and money saving.


    The money saving, especially in the long-period, is amongst the reasons why you should consider to select a diaphragm pump. The improvements made in diaphragms construction have indeed dramatically increased the life of the diaphragm pumps. They can work properly for years with a very low maintenance, especially thanks to their static seals. These seals maintenance indeed tends to be infrequent and inexpensive.

Have we convinced you? Visit the webpage of our HAOD in order to learn more about air operated pumps. For further information contact us at info@gemmecotti.com. Our technical and sale departments will be glad to lead you to the best choice.

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Pressure vs head, what is the difference?

The pump selection of a pump is driven by the following main parameters:
– Head (H)
– Flow rate (Q)
– Fluid characteristics (ρ, γ, T ….)
Sometimes head can be confused with pressure during pump choice. As a matter of fact there is a strict relation between them which is defined by the fluid specific gravity, so the relation is fluid dependent. So what is the difference between pressure and head?

Definition of head and pressure

Head is the height given by the pump to the fluid and it is measured in meters of liquid column [m.l.c.] or simply indicated in meters [m]. The given head is fluid independent: different fluids
with different specific gravities are all lifted at the same height.
Pressure, instead, is fluid dependent and it is affected by the liquid density. In fact the force of a fixed height liquid column over a unitary area will change with different specific gravities. So in this case the same head generates different pressures.

Measurements: Pressure or Head?

Head is not directly measured. Manometers on the pump suction and delivery line give the measure of the pressure. Measurements given by manometers indicate differential pressures imposed by the pump between suction and discharge. These measures are read in [bar] [atm] [psi] [ft H2O] etc.. Specific gravity γ has to be considered to evaluate the correspondent head.

Conversions & Practical Example

As stated before, the same pump at the same working point will give always the same head with different pressures in accordance with the density γ of the working fluid.
For example, a mag drive centrifugal pump HTM 10 working at a given point Q= 7.5 m3/h H = 10 mlc operating with water and concentrated H2SO4 gives the same head (H=10m) to water ( γ= 1kg/dm3) and to sulfuric acid (γ = 1.8kg/dm3), while measurements of differential pressures between suction and delivery will be:

equazione pressione 12

The mathematical relationship is reported in the following equation:

equazione pressione 1
Also power consumption is influenced by the previous relationship of pressure, as:

equazione pressione 2curve pressure

Notes for technicians

– Previous relations are valid for low viscosity fluids (water equivalent), along with increasing viscosity, pump performances have to be reduced using pump derating rules.
– At a fixed rotational speed a centrifugal pump generates head related to the flow rate following its characteristic curve.
– The computation of the needed head that should be delivered by the pump, is not so straight as the evaluation of the desired height difference. Needed Head is composed by the following terms:

  • Geodetic head: difference between suction and delivery height expressed in meters of liquid column

equazione pressione 3

  • Difference between absolute pressure of the delivery and suction reservoir

equazione pressione 4

  • Distributed and concentrated friction losses also expressed in m.l.c.
    equazione pressione 5
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How to read a pump curve

If you are new in the pump field, reading a pump performance curve (usually just called “pump curve”) can be difficult and sometimes confusing. That’s why we want to help you by offering a simple guide for a first approach to a pump curve.

What is a pump performance curve and why do you need to know how to read it?

A pump curve is a graphical representation of the performance of a pump based on the tests of the pump manufacturer. Every pump has its own curve and it varies very widely from pump to pump. The variation depends on many factors such as the kind of pump (centrifugal pump, turbine pump, vane pump etc.), size and shape of the impeller. Pump curves can be used to provide many information of pump performance and absorbed power which are important for a user to determine the working point and motor power and size.

What information can I find on a pump curve?

1- In the simplest and widely used pump curve (commercial multi-pump curve) you can see two vital pump performance factors: flow and head.

The flow or capacity (Q) is measured in m3/second according to the international standards but usually you can find it expressed in m3/h, l/min or gpm (in the US). It is the volume of liquid moved in an amount of time. On the curve below (Picture 1) you can see the flow marked in red on the horizontal axis.

The head (H) is the height at which a pump can raise a liquid up. It is measured in meters (m or mlc meter of liquid column) or feet and you can see it marked in blue on the vertical axis on the picture below.

Pump performance curve with flow and head


How can you read this pump curve?

To select the right pump model you should, first of all, identify the capacity and the head needed for  your system.

If you need for example a flow of 15 m3/h at 20 m you can find the right pump curve and consequently the right pump in the intersection of the two red arrows in the chart. In the example below the pump suitable is magnetic drive centrifugal pump model HTM 31.



The curve enables you to see how the pump will perform at any given point within its performance range. For example, the same pump model HTM 31 at 15 m3/h will produce a head of 20 m, or at 24 m of head the pump will generate a flow of 8 m3/h.

Once you have chosen the right pump type whether centrifugal, turbine, vane or any other, you can study in details the specific curve of the selected pump model with other technical information.

2– In picture 2 you can see an example of a centrifugal pump curve (HTM 31 PP/PVDF) with additional details than curve in picture 1 such as for example the impeller diameter (curve A circled in red), the NPSHr (curve B) and the absorbed power (curve C). In some case you can also find the pump efficiency.  This kind of curve is usually used by pump manufacturers to select the correct pump model among their set of performance curves.

Performance curve centrifugal pump


How can you read this pump curve?

In the title box at the top you can find the pump model, the number of poles of the motor, the frequency, the RPM and the pump material (selected according to the liquid to pump).

In curve A you can see the flow and head as described in the paragraph above but there is also a reference of the impeller diameter. For this pump model the available impeller diameters vary from a  minimum of   110mm to a maximum of 134 mm. The impeller would be trimmed by the manufacturer to whatever diameter needed to meet your conditions of service. If the impeller selection is 122 mm at a flow of 10 m3/h the head is about 19 mlc. The manufacturer would determine the proper impeller diameter for your conditions and trim it to the correct diameter.

Curve A - centrifugal pump

In curve B you can see the NPSHr of the pump measured in meters or feet in accordance with the capacity required. This is the minimum head at the suction of the pump that allows the pump to work properly. If sufficient NPSH available is not supplied by the plant (NPSHa) the pump will cavitate and this will affect both the performance and the pump lifetime. In case of 10m3/h capacity you have to find the intersection with the curve of the selected impeller diameter and read the value on the left.

Curve B - centrifugal pump

In curve C you can find  the absorbed power required for pumping a liquid with a SG of 1. Once determined the impeller diameter and the flow you can find the intersection where you can read the absorbed power, which is necessary to determine the relevant motor power.

Curve C - centrifugal pump

The correct selection of a pump using a pump curve is essential to permit a proper working of your system. A working point too far out on the curve, or too far back, can cause damage to the pump, excessive energy consumption, poor performance and pump failure.

For further information don’t hesitate to contact us www.gemmecotti.com



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Video: how to assemble and disassemble magnetic drive turbine pump HTT

Here is the new GemmeCotti video tutorial: how to assemble and disassemble magnetic drive turbine pump series HTT PP/PVDF. Enjoy!


Magnetic drive regenerative turbine pumps series HTT are made of thermoplastic non-metallic materials (polypropylene-PP and PVDF) and are suitable to pump high corrosive and dangerous liquids. Thanks to the innovative sealless mag drive system, pumps model HTT reduce risks of leakage and emissions and the maintenance costs are very low. The transmission of the motion occurs through magnetic joints without any mechanical seal. This design guarantees the maximum safety and efficiency.

Max capascity: 9 m3/h

Max head: 50 mlc

Max temperature: 70°C for PP pumps and 90°C for PVDF pumps

Contact our office for more information: info@gemmecotti.com


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Mag drive pump HTM 31 PP/PVDF now suitable for 4kw

Sealless Magnetic Drive pumps model HTM 31 PP/PVDF are now suitable also for 4 KW motor size 112. This pump model can be coupled to three different motor sizes:

SIZE 90 – 2,2KW
SIZE 100 – 3KW
new SIZE 112 – 4 KW
You can contact our sales department for more details.


What are the characteristics of mag drive pump model HTM PP/PVDF?

HTM PP/PVDF pumps are mag drive centrifugal pumps made of thermoplastic materials (PP and PVDF) and are suitable to pump high corrosive liquids.

Max capacity: 45 m3/h, Max Head: 33 mlc, Max
Temperature: 90°C Max viscosity: 200 cSt, Pressure rating NP 4 at 20°C.

Click here to find out more.


How does a magnetic drive pump work?

Sealless mag drive pumps have a particular sealless design that is suitable to pump corrosive and dangerous liquids thanks to the high chemical resistance and absence of leakage and emissions. The structure is really simple and requires a very reduced maintenance with consequent save in terms of repairing and spare parts costs during the pump life.
The external magnet, placed on the drive shaft, transmits the motion to the internal magnet connected to the impeller which rotates and moves the fluid through the pump.

Here is a sketch of the functioning of magnetic drive system.Mga drive pumps



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How can you prevent dry running of pumps? 

One of the main reasons of pump damage is the dry running due to functioning without liquid, so it is important to pay attention and never let a pump operate without liquid inside. Moreover, if you think about it, the main purpose of hydraulic pumps is to transfer a fluid, so letting the pump work without liquid is useless and it’s a huge waste of energy.

What happens when a pump runs dry?

When a pump works without fluid there is a sudden increase of  the internal temperature with destructive results of some pump parts.

For example, when a plastic pump (in PP or PVDF) runs dry, the main damage occurring are:

1- the shaft in ceramic may broke due to a thermal shock.

2- the rotating bushing may block on the shaft.

3- melting of some plastic parts (impeller, rear casing, internal magnet etc.) due to the sudden temperature rise.

 How is it possible to prevent dry running?dry running protection

To avoid the inconvenience of the dry running you can simply install a dry running protection device which stops the pump immediately in case of danger of dry-running. As a matter of fact, the device checks constantly the active power of the motor, which is the minimum value of the instantaneous power absorbed by the pump, through the reception of information about the voltage, the cosφ and current variations. Through a set point and a timer, which are adjustable, it’s possible to set the minimum power and the triggering time of the device. If the power goes under the established value, the pump stops and the device must be switched on again manually. In case of continuous intervention on the apparatus,  check the presence of liquid and/or the correct functioning of the plant to find the cause of working of the device.

Click here to find out more.

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Do you know that GemmeCotti pumps can be used in car washing machines?

pumps in car washing plantsGemmeCotti pumps are used in many industries for different applications among which also car washing plants. Chemical pumps in car washes are installed with the main purpose of dosing and spraying water containing detergents and chemicals of various kinds through high-pressure jets. So it is necessary to use an efficient and reliable high-pressure pump to guarantee clean and shiny vehicles.

Our experience in car washes

We have a lot of experience in this particular field and recently we have worked on a new project which required a pumping equipment with very high pressure for a wheel rim cleaning system in a car wash machine. The customer required a pump suitable to transfer a detergent from a 40-liter-tank to the oscillating jets of the machine. The fundamental requirement for the pump was the discharge pressure which had to be at least 6 bar. We studied carefully the application and in the end we proposed our metallic rotary vane pump series HTP that can reach a maximum pressure of 13 bar.

High pressure vane pumps for car washing machines

The pump model HTP that we selected for the application is a positive displacement pump with vanes made of stainless steel AISI316. In this pump the vanes in graphite are mounted in a rotor and they move inside a cavity sliding into and out of the rotor. In this way the fluid is pumped outside the pump with a pressure up to 13 bar and a maximum flow of 2000 l/h. Click here

GemmeCotti rotary vane pumps model HTP

Mag drive vane pump HTP

to watch how a vane pump works.

Vane pumps model HTP in AISI 316 are suitable for detergents, hydrocarbons, solvents, heat transfer oils, refrigerants and cryogenics or other thin no-lubricating liquids. Thanks to the mag drive design these pumps are useful for low flow and high pressure applications such as car washes, pilot plants, sampling, flushing of mechanical seals and cooling units.


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How does a mag drive rotary vane pump work?

In a magnetic drive rotary vane pump two pumps design are combined together: the sealless magnetic coupling and the positive displacement system with vanes.

With the magnetic coupling the torque is transmitted through contactless magnetic forces from the external magnet which is coupled to the motor shaft to the internal magnet which is connected to an impeller or rotor. This design ensures a hermetic and reliable separation between the pump and the motor making it the best solution when pumping chemicals and acids because it prevents leakage and emissions.

A rotary vane pumping system consists of vanes mounted in a rotor that rotate inside a cavity. When the rotor moves thanks to the above mentioned mag drive system, the vanes slide into and out of the rotor creating vane chambers that do the pumping work.

For further information you can watch the video below or visit our website 

mag drive rotary vane pump GemmeCotti


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Video: how to assemble and disassemble metallic mag drive pump series HTM SS316

Here is the new GemmeCotti video tutorial: how to assemble and disassemble mag drive pump HTM SS316.


Mag drive centrifugal pumps model HTM SS316  are seal less pumps suitable to pump hydrocarbons, solvents and dangerous liquids and are made of AISI316. These metallic pumps have a special design in which the transmission of the motion occurs through magnetic joints (external magnet and internal magnet) without any mechanical seal. The external magnet is placed on the drive shaft and transmits the motion to the internal magnet connected to the impeller which rotates and moves the liquid through the pump.
This simple structure guarantees a very reduced maintenance with consequent save in terms of repairing and spare parts costs during the pump life. Click here for more information about HTM SS316 pumps.
Enjoy our video tutorial!

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Video: how to assemble and disassemble mag drive centrifugal pump HTM PP/PVDF

Here is the new GemmeCotti video tutorial: how to assemble and disassemble mag drive centrifugal pump HTM PP/PVDF. Click here or on the image below to watch the video

Video tutorial: how to assemble and disassemble mag drive pump HTM PP/PVDF



Mag drive centrifugal pumps series HTM PP/PVDF are chemical seal less pumps suitable to pump high corrosive fluids and are made of polypropylene or PVDF. These kind of pumps for acids has a special design in which the transmission of the motion occurs through magnetic joints (external magnet and internal magnet) without any mechanical seal. The external magnet is placed on the drive shaft and transmits the motion to the internal magnet connected to the impeller which rotates and moves the liquid through the pump.

This simple structure guarantees a very reduced maintenance with consequent save in terms of repairing and spare parts costs during the pump life.

Watch our video tutorial for more information!


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That’s how you can unload tank trucks and IBC containers

When you have to unload a tank truck or an IBC container you need to use a suitable pump resistant to corrosion that can be easily moved. That’s why we designed a pumping system which is portable and composed of chemical resistant mag drive centrifugal pump series HTM PP/PVDF. The peculiarities of this device are that it is flexible for different uses, and it is portable.

The pump is placed in a proper structure that can be removed from an IBC container’s attack and connected to another, thanks to quick couplings, ensuring anyway all of its functionalities.

H-IBC portable pump GemmeCotti



The displacement of the pump is easy and rapid, as a result of its compact shape and its practical handles, located on the top. The system includes a control panel composed by illuminated start and stop pushbuttons, a red LED for power on, an emergency stop button with manual restoration and a flexible supply cable with CEE plug. There is also a specific container in order to collect dropping fluid. As an optional, it is possible to order a dry running protection device and a frame with wheels for an even easier portability.


Materials available: PP and PVDF
Max capacity: 13 m3/h
Max head: 14 m
Standard motor: 0,55 kw, B3/B5, 2poles, single phase, 230V, 50-60HZ
Baseplate: included



GemmeCotti H-IBC portable pump main applications


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5 things to keep in mind when installing a pump

The pump is generally part of a hydraulic system that can include a various number of components such as valves, fittings, filters, expansion joints, instruments, etc. The way the piping is arranged and the position of the components has a great influence on the operation and on the life of the pump. Here are five things to keep in mind when installing a pump in a plant:

  1. Locate the pump as near as possible to the liquid source and under the level of the liquid (in case of non self-priming pumps). Always use pipes as short and straight as possible and limit the number of bends assuring radius of curvature as large as possible. This would avoid air vortex that can be created in the long piping line. Avoid the creation of siphon also before the suction of the pump.
  2. Do not load the pump with the weight of the pipes. The piping should be properly supported and kept in line independently from the pump, until its connections, so that the piping doesn’t exert loads on the pump.
  3. The sizes of the suction and discharge pipes have to be at least as large as the inlet connection of the pump. Diameter restriction of the suction pipe is responsible and cause of the cavitation of the pump, creating a loss in the performance of the pump and a rapid wear. It’s advisable always to use (if in case) flexible reinforced pipes that don’t collapse under a situation of depression
  4. A check valve should be installed on the discharge pipe to avoid the liquid to flow back when the pump is stopped.
  5. The suction line has to be clean and/or contain a filter to protect the impeller from damage due to impurities, or other foreign particles, especially when starting the plant for the first time.
  6. Don’t use metallic piping with plastic pumps to avoid cracks on pump connections and make sure that the connections are properly tightened otherwise the suction capacity will be reduce

The easy rules written above are very important for the correct installation of a pump but if you want to check also the correct functioning you could:

  1. Install a  proper pressure gauge on both the suction and discharge piping which allows a control of the functioning in relation to the required working point. In case of cavitation or other dysfunctions, the gauges will show evident pressure fluctuations.
  2. Install a wattmeter to monitor the electric power absorbed by the motor to avoid dry running of pumps.

Few precautions can prevent pump failures and consequent losses of time and money for repair.


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How can you install a pump perfectly horizontal?

When installing a chemical pump with motor configuration B3/B5 in a plant it’s really difficult to maintain it perfectly horizontal because of the heavier weight of the pump with respect to the motor and/or the form of the motor flange which doesn’t allow a balanced placement. So in this case how can you install a pump horizontal?

GemmeCotti technical office designed special baseplates to solve this problem. As a matter of fact, the pump complete with motor can be easily assembled to the baseplate thanks to the holes pre-drilled on the surface so that it can remain in position and perfectly horizontal. The baseplates are made in reinforced PP  and are available in three different sizes and they can be assembled with IEC and NEMA motors with B3/B5 form, from 0,12 kW to 4 kW.

The positive aspects of this solutions are:

– strong structure resistant to the pump weight and vibrations

– easy and fast assembling of the motor to the baseplate     

– material of construction resistant to acid corrosion

– safety installation of the pump

– cheap solution to a problem that can be faced in a plant


Sometimes customers think that it’s not necessary to spend money to buy a baseplate because they can “invent” and create their own structure to keep the pump in position. But is it really cheaper? There’s always the designing process to consider in addition to the purchase of the parts to use and obviously the time and workmanship for the realization of the structure.

Adding all these costs it’s clear that a little investment for a baseplate already built and ready to be installed in the end could be a great benefit.


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Mag drive vs Mechanical seal pumps: which are the advantages and disadvantages?

In applications where chemicals, acids and corrosive liquids are involved it’s necessary to pay a great attention to the kind of pumps used and sometimes it’s difficult to choose between seal or sealless pumps. So which are the advantages and disadvantages of mag drive sealless pumps in comparison a with mechanical seal pumps? This is the neverending debate for pump manufacturers and pump users and in this article I would like to point out some aspects to keep in mind when choosing the pump design.


Mag drive pumps have a particular sealless design where the pump is closed coupled to the motor. The external magnet placed on the drive shaft transmits the motion to the internal magnet connected to the impeller which rotates and moves the fluid through the pump. The external magnet and inner magnet are separated by a rear casing that creates a hermetic containment of the liquid that has no access to the outside


  1. This special hermetic pump design prevents any leakage of fluid and fugitive emissions, that in case of chemicals, corrosive liquids, explosive and flammable fluids could be very dangerous for people dealing with the pump and especially for the environment. So mag drive pumps allow to follow strict environmental and safety objectives required by many regulations.  We shouldn’t forget also that some liquids could be very expensive and their loss due to a seal failure may cause high unnecessary extra costs.
  2. Mag drive pumps are very reliable and need very low maintenance thanks to their simple design. With normal working conditions these pumps can work without any kind of repair for more than a decade so their life cost is highly reduced  even if it’s always better to check o-rings and bearings every one/two years just to be sure that there is no wearing.
  3. The coupling is very easy because there is no need for a motor/pump alignment.


  1. In applications involving even a small percentage of solids the mag drive system is not the suitable solution. Magnetic drive pumps, in fact, can work only with clean liquids without solids in suspension.
  2. Magnetic drive pumps are usually more expensive than mechanical seal pumps. However, as written above, the maintenance costs are very reduced during the life of the pump and these long-term financial advantages should be considered when choosing the pump design.



The seal in mechanical seal pumps is composed by a static ring and a rotating ring placed on the pump shaft which is directly coupled to the motor shaft. The two surfaces sliding together need to be lubricated and the seal lubricant is the liquid itself that is being pumped.


  1. Mechanical seal pumps are the perfect solution for applications involving solids in the liquid (for example waste water treatments) because their design with open impeller allows to pump very dirty liquids and fluids with high viscosity.
  2. The cost of this kind of pumps is lower in comparison with mag drive pumps so, if the financial aspect is critical when choosing the pump, sealed pump may be the right selection.


  1. Seals are often the weak point in standard pumps because they are the first cause of failure in a chemical process. When a mechanical seals fails it allows the liquids to escape causing dangerous leakage.
  2. Considering the point above, to avoid harmful events and dangerous leakage it’s necessary to plan a periodical maintenance of mechanical seal pumps to check the status of the seal and replace worn parts. In this case the costs of maintenance of these pumps could be higher than those of mag drive pumps.

In some applications it’s possible to install both mechanical seal or mag drive pumps and technicians can decide according to the advantages and disadvantages of each pump which is the best for them.

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There’s a suitable material for each application

In my latest article about the different materials used for chemical pumps I wrote a brief guide helpful for a first materials selection according to their properties and characteristics. Now I would like to analyze each material from the point of view of their typical applications.


Polypropylene (PP):

Mechanical applications: PP is used for mechanical parts in corrosive environments. Compared to polyethylene with a high molecular weight, polypropylene has a higher traction resistance.

Alimentary applications: physiologically inert when it has a natural color, polypropylene is suitable for  use in contact with foods.

Electrical applications: good dielectric characteristics and weather-proof.

Chemical applications: PP is widely used in chemical industries because of its high resistance to acids and alkali. Thanks to its higher resistance to temperature than PVC  it’s used for valves, flanges gears etc. in chemical, galvanic and petrochemical industry. It’s not suitable for use with high concentration oxidizing acids.



Chemical applications: the high chemical resistance to acids and alkali is typical of fluorinate polymers (PVDF) that’s why it’s mainly used for parts in petrochemical and chemical industries.

Alimentary applications: physiologically inert when it has a natural color, it’s approved by different organizations for use in contact with foods. It’s often used because of this characteristics, especially in alimentary machines and in pumps for alimentary liquids.

Electrical applications: good dielectric characteristics, self-extinguishing without adding halogens and weather-proof

Mechanical applications: the low friction coefficient makes is suitable for bearings even if they work in water.



Mechanical applications: the low coefficient of friction makes it useful for bearings unless they have to support a great weight.

Alimentary applications:  physiologically inert, it’s approved for use in contact with food by some organizations, but in some countries it’s questioned the possible use in contact with food.

Electrical applications: thanks to the good dielectric characteristics, the self-extinguishing and the stability to bad weather it’s used more and more in this field.

Chemical applications:  typical of fluorinate polymers is the high chemical resistance to acids and alkali. It’s main use is for components in petrochemical and chemical industry.



Mechanical applications: Gaskets, section bars and technical items for cars, handmade articles for anti-acid protections.



Suitable for plants for production of nitric and sulphuric acid and for the relative equipment (pumps, valves and pipes). It’s used in very aggressive environments (textile industry, paper industry, oenological- alimentary  industry, and especially naval industry).

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A brief guide to choose the suitable pump materials for chemical applications

When dealing with acids it’s important to use suitable chemical pump materials resistant to corrosion which are highly efficient and require minimum maintenance. That’s why, after years of experience in chemical pumps field, we decided to use Polypropylene, PVDF and AISI316 as standard materials for our pumps and EPDM, Viton and PTFE for the o-rings.

Every material has its own properties and characteristics that make it suitable for pumping different acids because, as I wrote in my previous article about pump selection, it’s really important to choose the right pump material for every chemical application.

 Polypropylene (PP)

  1. Polypropylene is well known with the name Moplen (™)
  2. It’s a thermoplastic material extremely resistant to many solvents, bases and acids such as for example acetone, caustic soda and chloridric acid.
  3. It’s not suitable for concentrated, oxidizing acids.
  4. It’s used in many different industries for parts subjected to relatively modest forces.
  5. Temperature range for PP pumps is from 4° to 60°C.

Polyvinylidene fluoride (PVDF)

  1. It’s a thermoplastic material of the fluoropolymer family and it’s used generally in special applications requiring the highest purity, strength, and resistance to solvents, acids, saline solutions, to alkali and bases.
  2. It’s mainly used with liquids such as for example sodium hypochlorite, concentrated sulfuric acid, nitric acid, gasoline.
  3. It doesn’t undergo deformation under loads and has a high mechanical resistance.

  4. Temperature range for PVDF pumps is from -40° to 90°C.

 Stainless steel AISI316

  1. It’s a metallic material used when both the properties of steel and the resistance to corrosion are required.
  2. Particularly indicated for pumps working with high temperature liquids, oils, kerosene, alcohols.
  3. It’s used to pump acids up to a maximum temperature of 160°C

Also the o-rings are in contact with the liquid and their material is very important to avoid leakage.


  1. It’s an elastomer with a good resistance to heat, ketones, ordinary diluted acids and alkalines.
  2. Temperature range: from -40°C to 140° C

  3. We usually use EPDM o-rings as standard with PP pumps


  1. It’s a fluoropolymer elastomer with a good resistance to hydrocarbons, acids, fuels, mineral and vegetable oils but it’s incompatible with ketones and organic acids
  2. Temperature up to 150°C
  3. We usually use VITON as standard with PVDF and AISI316 pumps


  1. Polytetrafluoroethylene known also as Teflon (™).
  2. It’s highly resistant to the attack of acids and basis  in corrosive environments but it has poor mechanical properties such as traction and compression.
  3. T

    emperature range: from 4°C to 260°C

These are general rules that can be useful for chosing pump material but it’s better to consult a good chemical compatibility chart to select the best material for each chemical application.

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Five things you should know about Atex Pumps

When operating in a potentially explosive atmosphere it’s necessary to use a suitable pump designed and manufactured according to the ATEX directive 2014/34/EU. Here are five main things you should know when dealing with Atex Pumps:


  1. Equipment used in potentially explosive atmospheres is divided into groups and categories according to the degree of protection offered. You can see and example in the table below.
    Atex groups and categories

    Table 1 – Atex groups and categories

  2. Pumps for use in potentially explosive atmospheres will normally be classified under Group II, Categories 2 and 3. It is the responsibility of the end user to classify the zone and the corresponding group (dust or gas) in accordance with the EC – Directive 1992/92/EC. Once the pump manufacturer knows the Atex classification needed by the customer, it’s possible to select the right pump solution.
  3. Atex pumps have a special design which prevents the formation of sparks and the ignition of explosive atmospheres that may be produced or released by equipment. They must be assembled to Explosion proof motors with the same safety measures.
  4. Atex pumps for zone 1, where explosive atmosphere caused by gases, vapours, mists or air/dust mixtures are likely to occur, must be equipped with safety devices like dry running protection and thermoprobe PT 100. The dry running protection checks constantly the active power of the motor, which is the medium value of the instantaneous power absorbed by the pump, and prevents the dry-running of the pump, the closed discharge and the blocked suction. PT100, instead, is a resistance temperature detector used is used for monitoring the operating temperature of the pump.
  5. Atex pumps need a certification issued by the manufacturer and shall be marked with the following information:
    Atex mark

    Atex mark

  • name and address of the manufacturer
  • CE marking
  • series type, year of construction and serial numer
  • the specific marking of explosion protection followed by the symbol of the equipment group and category


The European Commission issued a guideline to facilitate the application of Atex directive 2014/34/EU which could be useful for the first approach to Atex products.

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Why is NPSH important for pump selection?

One of the important aspects to keep in mind when installing a pump in a plant is NPSH (net positive suction head).  There are two values of NPSH: NPSH available calculated by the plant engineer, and NPSH required which depends on the characteristics and performances of the pump. So why are these data so important?


NPSH available

The term is normally shortened to the acronym NPSHa where the ‘a’ denotes ‘available’. It is the result of the absolute pressure of a fluid at the inlet to a pump minus the vapour pressure of the liquid.


NPSH required

This is a term used by pump manufactures to describe the energy losses that occur within many pumps as the fluid volume is allowed to expand within the pump body. This energy loss is expressed as a head of fluid and is described as NPSHr (Net Positive Suction Head requirement) where the ‘r’ suffix is used to denote the value is a requirement. Different pumps will have different NPSH requirements depending on the impeller design, the impeller diameter, the flow rate, the pump speed and other factors. A pump performance curve will usually include a NPSHr graph so that the NPSHr for the operating condition can be established.


Avoiding cavitation

The essencial condition to have a good pump functioning is that NPSHa is higher than NPSHr to avoid cavitation.

NPSH scheme

Cavitation is the formation of gas bubbles when the pressure within a fluid falls below its vapour pressure. If a fluid which contains gas bubbles is allowed to move through a pump, it is likely that the pump will increase the pressure within the fluid so that the gas bubbles collapse. This will occur within the pump and reduce the flow of delivered fluid. The collapse of the gas bubbles may cause vibrations which could result in damage to the pipework system or the pump. This effect is known as cavitation.



Correct pump selection

In order to choose the correct pump size, it’s always important to know the NPSHa and check if it is suitable with the NPSHr of the pump. Once the relationship between these values is right the pump will work correctly and cavitation will not occur.



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How to easily select a pump for acid

If you need to select a chemical pump, first of all you should find out some important technical data which are extremely useful for the right choice of pump: capacity/flow and head/differential pressure required, kind of liquid, temperature, viscosity, possible presence of solids in suspension and if possible also NPSHa.


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