Internal sealing of the check valve
disc and seat relies on “reverse” line
pressure as opposed to the mechanical
force used for on/off valves. Because of
this, allowable seat leakage rates are
greater for check valves than with on/off
valves. MSS SP-61 “Pressure Testing of
Steel Valves,” published by the Manufacturers
Standardization Society, is
one standard used by manufacturers to
perform seat and shell closure tests for
check valves (as well as other valves).
Factors affecting check valve seat leakage
include reverse pressure, medium,
and what the seat material is made of,
such as metal or elastomer. Metal
sealing surfaces generally will allow
some leakage while elastomers such as
Buna-N and Viton provide bubble-tight
shutoff (zero leakage). Because of this,
elastomers should be considered for
air/gas media and low-pressure sealing.
Important considerations when using
elastomers for such valves are service
temperature and compatibility of the
elastomer with the medium.