Diaphragm seals are devices used to protect pressure instruments, such as pressure gauges, transmitters and switches, from the process media they are measuring. They are commonly used in various industries to prevent the process fluid from directly contacting and potentially damaging the sensitive components of the pressure instrument. Diaphragm seals come in different types, and the choice of seal depends on the specific application and requirements. Here are some common types of diaphragm seals used for pumps:
1. Metallic diaphragm seals
Metal diaphragms: Metal diaphragms of stainless steel (several grades), Carpenter 20, Hastelloy, Monel, Inconel, tantalum, titanium and several other metals are in common use where high-pressure ratings and specific chemical compatibility are required. Flanged assemblies or flush welded versions are available.
2. Elastomeric diaphragm seals
Rubber diaphragms: These are diaphragms made from materials like rubber or elastomers. They are flexible and are used in applications where a lower pressure range is expected.
Polytetrafluoroethylene (PTFE) diaphragms: PTFE is a nonreactive and chemically resistant material. PTFE diaphragm seals are suitable for corrosive and aggressive media.
3. Composite diaphragm seals
Used in toxic environments: Composite diaphragms are used everywhere toxic and chemically aggressive agents are conveyed.
4. Sanitary diaphragm seals
Designed for hygienic applications: These diaphragm seals are specifically designed for industries like pharmaceuticals, food and beverage and biotechnology where cleanliness and hygiene are critical.
5. Flush diaphragm seals
Designed for cleanability: Flush diaphragm seals have a smooth, flush surface that is easy to clean. They are commonly used in applications where hygiene is essential, such as in the food and pharmaceutical industries.
6. Extended diaphragm seals
Used in high-temperature applications: These seals have an extended diaphragm to isolate the pressure instrument from high temperatures.
7. Specialty diaphragm seals
Some diaphragm seals are designed for specific applications, such as high-purity applications, cryogenic applications or applications with aggressive chemicals.
These seals can be produced to meet Food and Drug Administration (FDA), United States Pharmacopeia (USP) Class VI, National Sanitation Foundation (NSF) 51 or 3-A Sanitary Standards. Standard materials include nitrile butadiene rubber (NBR), neoprene (CR), silicone rubber (VMQ) and ethylene propylene diene monomer (EPDM). High-performance, high-temperature resistant elastomers such as fluoroelastomers (FKM), hydrogenated nitrile butadiene rubber (HNBR), fluoro vinyl methyl silicone rubber (FVMQ) and perfluoroelastomer (FFKM) can be utilized.
In the processing industry, diaphragm seals are mostly found in actuators, fittings, hydraulic accumulators, pumps, compressors, valves and regulators. When incorporated into a pump system, a diaphragm seal can offer
several advantages:
Chemical compatibility
Diaphragm seals are available in a variety of materials, allowing for compatibility with different types of process fluids. This is especially important when dealing with corrosive or abrasive substances, as it protects the pressure-measuring instrument from direct contact with the fluid.
Corrosion resistance
In applications where the process fluid may be corrosive, a diaphragm seal acts as a barrier, preventing direct contact between the corrosive fluid and the sensitive components of the pressure-measuring instrument. This helps extend the life
span of the instrument and reduces maintenance requirements.
Hygienic applications
In industries such as pharmaceuticals or food and beverage where hygiene is crucial, diaphragm seals can be made from materials that comply with sanitary standards. This ensures the pressure-measuring instrument remains uncontaminated and suitable for use in sensitive environments.
Temperature extremes
Diaphragm seals can be designed to withstand extreme temperatures. This is particularly useful in applications where the process fluid is at high or low temperatures, as it helps protect the pressure-measuring instrument from thermal damage.
Pressure pulsation damping
In pump systems, pressure pulsations can occur, leading to inaccurate pressure readings. Diaphragm seals can act as a buffer, dampening pressure fluctuations and providing a more stable and
accurate measurement.
Easy maintenance
Diaphragm seals are often designed for easy removal and replacement. This simplifies maintenance and reduces downtime, as the pressure-measuring instrument can be replaced or serviced without interrupting the entire system.
Extended instrument life
By protecting the pressure-measuring instrument from harsh process conditions, diaphragm seals contribute to the longevity and reliability of the instrument, resulting in reduced replacement and maintenance costs over time.
Versatility
Diaphragm seals can be used in various applications and industries, making them a versatile solution for different pressure measurement needs.
While diaphragm seals can offer advantages in certain applications, they also come with some disadvantages
when used in pumps. Here are some potential drawbacks:
Cost
Diaphragm seals can be relatively expensive compared to other types of pressure measurement instruments. The initial investment and installation costs may be higher, which can be a significant factor in budget-conscious projects.
Maintenance
Diaphragm seals require regular maintenance to ensure they are properly functioning. Over time, the diaphragm can wear out or become damaged, leading to leaks and inaccurate pressure readings. Maintenance can be time-consuming and may result in downtime for the system.
Compatibility issues
Diaphragm seals may not be suitable for use with certain types of fluids or aggressive chemicals. Incompatibility with the process media can lead to chemical reactions, corrosion or degradation of the diaphragm seal, affecting its performance and life span.
Temperature limitations
Diaphragm seals may have temperature limitations, and exposure to extreme temperatures can impact their integrity and reliability. High temperatures can lead to thermal expansion or degradation of the diaphragm material, while low temperatures may cause the material to become brittle and prone to cracking.
Response time
The presence of a diaphragm seal can introduce a delay in pressure measurement response time. This delay may be acceptable in some applications, but in processes where rapid pressure changes occur, the response time of the diaphragm seal may be a limiting factor.
Potential for clogging
In applications with particulate-laden fluids, there is a risk of the diaphragm seal becoming clogged, which can affect its performance and accuracy. Regular cleaning or filtration may be required to prevent clogging issues.
Installation complexity
Installing diaphragm seals correctly can be more complex than installing direct-mount pressure instruments. Proper installation is crucial to ensure accurate pressure readings, and improper installation may lead to leaks or other issues.
Size and weight
Diaphragm seals can add bulk and weight to the overall pressure measurement system. In some applications, especially those with space or weight constraints, this may be a disadvantage.
Despite these potential issues, diaphragm seals remain a viable option in many industrial applications where they can provide reliable and accurate pressure measurements in challenging conditions. The decision to use a diaphragm seal should be based on a thorough understanding of the specific requirements and constraints of the application.
