The rubber liner butterfly valve torque will go up or down

[bao2ye]

Normally how long is the lifetime for an EPDM liner. Will the torque goes up with the aging of the EPDM liner for butterfly valve?

Thanks

 

[JimCasey]

EPDM liner will last for years on a water service.
It will be ruined after a few minutes if the service contains hydrocarbons. Or if (as I have seen) the maintenance apes lubricate them with diesel fuel when installing them in the valve body. Proper assembly lube: silicone grease. Even soapy water is good. Not diesel fuel or other petroleum product. Hydrocarbons make EPDM swell and get soft. A year or so on low-pressure steam less than 250F(120C)
If the service is gritty, reduce the OD of the vane to keep it from scrubbing the grit into the vane. (Called Undercut disc) This reduces the pressure limit at which the valve will shut off, but at low pressures (less than about 75 psi) it lasts longer and requires less torque with unndercut disc.

 

[NGiLuzzu]

Does anybody know a website showing a picture or a sketch of an "undercut disc"?

Many thanks in advance, 'NGL

 

[JimCasey]

They look just like any other disc. They just have a slightly smaller OD.

 

[NGiLuzzu]

Thank you, Jim!