With regard to valve seating, PTFE is a more harder material and does not have the plasticity of elastomers such as Viton, Buna, EPR etc. Selection of PTFE/Elastomeric seats should be driven by the application. In the past we limited PTFE to higher temperatures but had to heat the valve up during shop floor testing (simulating the actual process condition) in order to obtain a better seal.
*** Per ISO-4126, the generic term 'Safety Valve' is used regardless of application or design ***
*** 'Pressure-relief Valve' is the equivalent ASME/API term ***
The major difference, PTFE is a plastic and elastomers rubber. PTFE is good for static applications, not so good for dynamic. PTFE is often coated on to an elastomers for applications that require resilience.
Major differences in Poisson's ratio, tensile strength, low temperature rating, high temperature rating, tensile strength, compressive strength, chemical compatibility, wear resistance, creep, machineability, hardness (durometer), cost, and a several more things. Only listed some of the major differences.
