Mechanical seal pumps with a semi-open impeller, such as the HCO type, are generally used for pumping acids and hazardous liquids when solids are present in the fluid, making it impossible to use magnetic drive pumps.
Their semi-open impeller design allows the safe transfer of corrosive liquids even when particulate matter is present.
The mechanical seal in these pumps consists of a stationary ring and a rotating ring mounted on the pump shaft, which is directly coupled to the motor shaft. The two contact surfaces must be lubricated, and this occurs through the pumped liquid itself.
Choosing the right mechanical seal for a centrifugal pump is essential to ensure safety, reliability, and long operational life, especially when pumping corrosive and aggressive liquids.
The GemmeCotti HCO centrifugal pump series, made of PP or PVDF, is available with different mechanical seal configurations designed to meet a wide range of industrial applications and operating conditions.
What seal types are available on HCO pumps?
The GemmeCotti HCO centrifugal pump range offers several sealing solutions, selected according to pump size, operating conditions, and the type of processed fluid. The main seal types available are:
- Elastomer Lip Seal – used on models HCO 95-10. This is a very simple and cost-effective solution for less demanding chemical applications with reduced performance.
- Single internal mechanical seal with PTFE bellows – adopted on models HCO 110-170. It combines high chemical resistance with excellent reliability thanks to PTFE bellows and the materials used for the seal faces (Standard: SiC / Ceramic; available on request: Graphite / Ceramic).
- Single internal mechanical seal with PTFE nellows, available on models HCO 180-200. Generally supplied in SiC / Ceramic, ideal for pumping acids and corrosive liquids under standard operating conditions with a maximum solids content of 3% and particle sizes not exceeding 5 mm. It allows high flow rates up to 130 m³/h.
- Double back-to-back mechanical seal – available on models HCO 180-200 for more critical applications. This seal guarantees the highest safety level thanks to a dual sealing system with barrier fluid. It is recommended for dangerous or aggressive fluids, maintaining the same high capacity (up to 130 m³/h) even under severe operating conditions.
🔗 Discover all HCO versions and available seals
What is a single mechanical seal and when should it be used?
A single mechanical seal consists of one sealing interface between the rotating shaft and the pump casing. It is the most common solution in centrifugal pumps for standard chemical applications.
In GemmeCotti HCO pumps from size 110 to 170, the single seal can be supplied in different materials depending on the pumped fluid. The standard version includes stationary and rotating rings in SiC / Al₂O₃, while an alternative stationary graphite ring is available on request.
On models HCO 180 and HCO 200, the seal rings are made of Silicon Carbide / Ceramic, ensuring good wear resistance, operational reliability, and an optimal balance between performance and cost.
Single mechanical seals are particularly suitable when the pumped fluid is not highly hazardous and when operating conditions (pressure, temperature, chemical composition) remain within standard parameters. In such cases, they provide high performance with a simple, economical, and maintenance-friendly design.
Advantages of a single mechanical seal
- Simple and compact design
- Lower initial investment compared to double seals
- Reduced maintenance needs thanks to fewer components
- Reliable pumping of acids and corrosive liquids under standard conditions
Typical applications
- Transfer of chemicals in industrial plants
- Water and chemical wastewater treatment
- Standard chemical processes where extra safety is not required
When handling highly dangerous, abrasive fluids or particularly critical applications, a double mechanical seal is recommended for higher safety.
What is a double mechanical seal and why is it suitable for critical applications?
A double back-to-back mechanical seal consists of two seal faces mounted opposite each other inside the seal chamber, with an interposed barrier fluid that ensures proper lubrication and heat dissipation.
This configuration offers a higher safety level and is the preferred solution for heavy-duty and critical applications where a single seal is not sufficient to contain the pumped fluid.
On GemmeCotti HCO centrifugal pumps, the back-to-back double seal is particularly suitable for pumping dangerous, corrosive fluids or liquids containing suspended solids up to 5% with particle sizes under 5 mm, as well as abrasive particles, while maintaining high performance and long-term reliability.
Advantages of a double mechanical seal
- Greater safety: significantly reduced risk of leakage, especially with hazardous or toxic fluids
- Environmental protection: better containment and prevention of contamination
- Longer service life: two seals reduce stress on each face, extending durability and lowering maintenance frequency
- Reliability in severe conditions: ideal for abrasive fluids, high temperatures, and demanding operating conditions
The choice depends on the liquid type, operating conditions, temperature, and plant safety requirements.
What materials are used in HCO centrifugal pumps with a mechanical seal?
All GemmeCotti HCO centrifugal pumps are made of high-performance thermoplastics, ideal for the chemical industry:
- PP (Polypropylene) – excellent chemical resistance, max temperature about 70 °C
- PVDF (Polyvinylidene Fluoride) – superior chemical resistance, max temperature about 90 °C
These materials ensure maximum corrosion resistance, long service life, and reliability.
How to choose the most suitable mechanical seal for an HCO pump
When selecting the right mechanical seal, it is important to evaluate:
- Chemical characteristics of the pumped fluid
- Hazard and toxicity level
- Operating temperature and pressure
- Required safety level
- Maintenance strategy of the plant
For standard chemical services, a single mechanical seal is often sufficient.
For dangerous or critical applications, a double mechanical seal is strongly recommended.
Is the pumped liquid clean? Magnetic drive pumps are the ideal solution to guarantee zero leakage and emissions into the environment, with extremely low maintenance. Learn more about the advantages of magnetic drive technology.
📩 For technical support and advice, contact the GemmeCotti team: info@gemmecotti.com
FAQ
1. What is the difference between a single and double mechanical seal?
A single mechanical seal uses one sealing face and is typically used in standard chemical applications where the fluid is not highly dangerous and operating conditions are stable.
A double back-to-back mechanical seal uses two sealing faces with a barrier fluid in between, ensuring higher safety. It is recommended when minimizing leakage risk is crucial, especially with toxic, dangerous, or highly aggressive fluids.
2. Are HCO mechanical seal pumps suitable for corrosive liquids?
Yes. GemmeCotti HCO centrifugal pumps are specifically designed for pumping acids and corrosive liquids.
They are made in PP or PVDF, high-performance thermoplastics that guarantee excellent chemical resistance and long operational life even in harsh industrial environments. Seal and gasket materials are selected according to the pumped liquid, temperature, and operating conditions.
3. Which seal is recommended for hazardous fluids?
For hazardous, toxic, or environmentally harmful fluids, a double back-to-back mechanical seal is strongly recommended.
It provides extra protection through the barrier fluid, reducing leakage risk and improving safety for both the plant and operators.
4. What is the maximum flow rate of HCO pumps with a mechanical seal?
GemmeCotti HCO mechanical seal pumps can cover flow rates from 0.5 m³/h up to 130 m³/h, with a maximum head of 48 meters.
The wide range available ensures the best solution for every application.
5. Can I get support in choosing the right seal?
Yes. GemmeCotti provides specialized technical support to help customers select the most suitable seal configuration.
The choice is based on the pumped fluid, operating conditions, safety requirements, and maintenance needs to guarantee the most efficient and reliable solution.
Contact GemmeCotti technical support: info@gemmecotti.com
6. Is a magnetic drive pump or a mechanical seal pump better?
The choice depends on the fluid characteristics and operating conditions.
- Magnetic drive pumps are ideal for clean fluids without solids, when zero leakage and minimal maintenance are required.
- Mechanical seal pumps, such as the GemmeCotti HCO series, are preferable when the fluid contains suspended solids or abrasive particles, or when high flow rates and more demanding operating conditions are needed.
