Page 208 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

190 Major Process Equipment Maintenance and Repair

Valve flutter, due to improper design can lead to valve failure. Experi-
ence shows that true valve flutter is not a frequent occurrence. When it
does occur, valves can be destroyed in a matter of hours. It takes ad-
vanced instrumentation to verify and solve valve flutter, however.
Pressure pulsations in suction and discharge piping of compressor cyl-
inders have been responsible for valve failures. Pulsations can be sus-
pected as the cause if there also is rapid wear, and possibly breakage of
the piston rings. This can be verified if there are bright marks on the en-
tire circumference of the liner the exact width of the ring and located at
the end of the ring travel. The trouble results because the pulsating pres-
sure gets behind the ring when the piston stops at each end of travel and
literally beats the ring against the liner. An exact study of piping size and
drum location is required to eliminate this problem.

Dirt and Llquid
Dirt and liquid are scourges to reciprocating compressors; unfortu-
nately, not much can be done about them. It is true that a better job is
being done in reducing installation dirt, thanks to better cleaning meth-
ods and a respect for the problem. But process dirt or fouling is some-
thing else again. One thing that concerns us is that screens are becoming
popular. They are being used both for start-up of new units and as perma-
nent installations. Screens are in some ways beneficial, but some people
are beginning to think they are the cure. They contend that with better
materials and design, the screens can be made fine enough to protect cyl-
inders. True, coarse particles that can be stopped by a screen are not
good for the equipment, but a cylinder will digest a certain amount of it.
However, it is the fine dirt that no screen will stop that has the worst
effect on the liner because it mixes with the oil and makes a perfect lap
for wearing parts. Furthermore, screens may load up and, if they break,
cause more damage than would have occurred without any screens at all.
In regard to polymerizing of certain gases, some chemical companies
claim success in injecting compounds into the suction nozzle of the cylin-
ders. The amount injected is about V2 gallon per hour per cylinder and it
increases the time between shutdowns for cleaning valves and cylinders
by four times. The same beneficial results may be obtained from using
diester-based synthetic lubricants for cylinder lubrication.

Knocks, Noises, and Vibration
Knocks, noises, and vibration are good indications of trouble. On the
other hand, normal noises are sometimes misinterpreted by even the ex-