Page 162 - Reciprocating Compressors Operation Maintenance

1 48 Reciprocating Compressors: Operation and Maintenance

Plastic Composites

Plastic plates, if correctly formulated and manufactured, have lower
differential pressure and temperature limits, about 1500 psi and 400°F for
PEEK (polyether-ether-ketone) based compounds and somewhat lower
for the nylon based materials.
They are, however, far superior to any metal element in resistance to
impact fatigue, corrosion resistant, and the ability to resist damage from
dirt and liquids.
Plastic elements cause very little seat wear and cannot cause damage
to the cylinder if they fail.
For optimum valve plate service at temperatures not exceeding 300°F,
asbestos-bakelite is a good choice. For higher temperatures, glass
melamine or glass epoxy is used, and, of course, the more recent PEEK
formulated materials should be given prime consideration.

Springs

The springs used on the sealing elements of valves include AISI 410
and 420 for feather and channel valves; for coil springs 17-4 PH, Inconel,
and cadmium-plated chrome-vanadium steels are used, depending on the
manufacturer and service conditions.
For all valve elements not only is the proper material important, but
rigid specifications and quality, such as flatness, dimensional tolerances,
and surface finishes are key considerations.

FUNCTIONS OF COMPRESSOR VALVE COMPONENTS

The compressor valve internal components are designed to survive the
simultaneous impact stresses imposed by a large number of cycles and
environmental stresses such as high temperatures, corrosive gases,
entrained liquids, gas pulsations, etc.
The compressor designer is responsible for choosing a valve assembly
to suit the application; however, it is the responsibility of the operator
and maintenance personnel to see that the valve assembly is properly
maintained.

* Valve seats must resist the differential gas pressure and wear on the
surfaces in contact with the valve sealing element (discs, strips, or
channels).