Page 170 - Reciprocating Compressors Operation Maintenance

156 Reciprocating Compressors: Operation and Maintenance

eliminated by proper construction and sizing (for low gas veloci-
ties) of separator internals.
4, Improper Lubrication
Valve life is shortened by excessive lubrication. It can cause stick-
ing of plates or strips, which delays reseating of the sealing element.
A delayed closing normally results in excessive slamming forces.
Excessive lubrication acts as liquid carryover and can cause the same
damage as condensate slugs or water contamination. Too much lubri-
cation of the discharge valves, especially if they are exposed to high
temperatures, often causes "coking " A carbon buildup will form on
the valve surfaces and become a flake-shaped impurity.

Abnormal Mechanical Action

This term covers the effects that substantially alter the normal opening
and closing motion of the valve. Included are:

• valve flutter
• slamming from delayed closing or other pulsations
• multiple impacting from excessive pulsations

Well-designed valves, with the proper spring load for a given applica-
tion, will do a good job. Their opening and closing motion will be such
that no harmful pulsations will occur. However, many valves are stan-
dardized for average conditions of operation and, when applied outside
this range, may malfunction. The right spring load of a valve depends on,
among other factors, its operating pressure, the gas velocity, and the spe-
cific gravity of the gas.
It is difficult to detect abnormal mechanical action, but careful analysis
is warranted of the surface where the sealing elements impact against
either the seat, upon closing, or guard, upon opening. If these surfaces
show wear related to impact (a hammered finish), assume that flutter or
multiple impact is the problem.
Abnormal mechanical action can also result from pulsations in the gas
stream. These may be caused by improper pipe selection or manifold siz-
ing, but with today's design technology available to the major compres-
sor builders, this is rarely the case.
The flow of gas to and from the valve is channeled around cages,
through cylinder openings, and cavities under and above the valve. The