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

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 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.

MAIN FEATURES:

• 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.

OPTIONAL:
• Pulsation damper.

CHECK THE TECHNICAL DATA AND DOWNLOAD THE COMPLETE CATALOGUE!

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.

NPSH AVAILABLE

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.

NPSH REQUIRED

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.

NPSH: WHY IS IT SO IMPORTANT?

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.

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.

NPSHa > NPSHr

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.

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

MAIN FEATURES OF MAG DRIVE PUMPS 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!

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.

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.

FEATURES OF THE PUMP

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

 MAIN APPLICATIONS: UNLOADING TANK TRUCK AND IBC CONTAINERS

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.

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

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

Advantages

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.

Disadvantages

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.

MECHANICAL SEAL PUMPS

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.

Advantages

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.

Disadvantages

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.

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.

PVDF:

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.

PTFE

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.

EPDM

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

AISI316

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).

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.

EPDM

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

VITON

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

PTFE

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.

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.
   

   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

• 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.

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.

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.

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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