A diaphragm seal is a flexible membrane that seals and isolates an enclosure. The flexible nature of this

seal Seal may refer to any of the following: Common uses * Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly: ** Earless seal, or "true seal" ** Fur seal * Seal (emblem), a device to impr ...

allows

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...

effects to cross the barrier but not the material being contained. Common uses for diaphragm seals are to protect pressure sensors from the

fluid In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...

whose pressure is being measured.

Materials

Since diaphragm seals need to be highly flexible,

elastomers An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus and high failure strain compared with other materials. The term, a portmanteau of ''elastic p ...

are commonly used, and include a wide variety of both general purpose and speciality rubbers. Elastomers are limited to low pressure applications and those that are chemically compatible with the various plastics and rubbers used. 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. Depending on the PSI levels of the sealing application, the diaphragm may require fabric reinforcement. Typically, PSI under 5 does not require fabric reinforcement. A PSI between 5 and 10 is application dependent. Anything above 10 almost always needs fabric reinforcement.

Applications

Diaphragm seals (also known as chemical seals or gauge guards) are also used to protect a process fluid from the pressure sensor. Examples of this use are: * Sanitary processes (food, pharmaceuticals, etc.) where allowing process fluid to accumulate in the pressure port of the sensor would compromise the purity of the fluid (such as milk getting into the pressure port of a pressure gauge and spoiling) * Very pure process fluids, where the metal surface of the pressure sensor might contaminate the fluid (such as copper ions from brass leaching into ultra pure water.) * Pneumatic systems where small changes in pressures must be eliminated, such as those controlling

air bearings Air bearings (also known as aerostatic or aerodynamic bearings) are fluid bearings that use a thin film of pressurized gas to provide a low friction load-bearing interface between surfaces. The two surfaces do not touch, thus avoiding the tradit ...

Seal failure

Diaphragm seals are susceptible to failure via several mechanisms, including cracking.

Ozone cracking Cracks can be formed in many different elastomers by ozone attack, and the characteristic form of attack of vulnerable rubbers is known as ozone cracking. The problem was formerly very common, especially in tires, but is now rarely seen in those ...

can occur in many elastomers for example used in pneumatic systems. If the gas contaminates the air supply, then many rubber diaphragms are at risk from the problem.

References

{{DEFAULTSORT:Diaphragm Seal Seals (mechanical)

Materials

Applications

Seal failure

See also

References