Page 165 - Reciprocating Compressors Operation Maintenance

Operation and Maintenance of Reciprocating Compressors 151

• Liquid carryover from a process or from interstage coolers is apt to
cause premature failures, particularly on intake valves. A slug of liq-
uid is particularly hard on valves and may even break a seat. Liquid
also destroys lubrication, thus, accelerating wear.
Carryover can result from poor separation of condensate ahead of the
compressor, or improperly designed piping where low spots permit liq-
uid accumulation. A sudden flow change can then cause a carryover.
It is important that interstage separators be drained regularly. Manu-
al drainage at specified intervals is preferred to automatic traps, partic-
ularly at higher pressure levels. Automatic traps, if used, should have a
bypass piped for visual observation and a check on their operation.
Liquid slugs can also be formed when saturated gas comes in con-
tact with the compressor cylinder walls. This can be prevented by
maintaining the compressor cylinder jacket water temperatures 1C) to
15 degrees above the temperature of the incoming gas stream.
Examination of the valve sealing element will sometimes indicate
liquid carryover or momentary high pressure damage, but liquid in a
cylinder is generally discernible by other means.
• Dirty gas causes all sorts of problems. It accelerates wear very rapid-
ly at all guiding points since it acts as a grinding compound. Foreign
matter between the coils of springs is a frequent cause of spring fail-
ure and subsequent failure of other valve parts.
• Carbon or sludge resulting from an unfortunate combination of a par-
ticular oil and the gas being compressed may hinder proper valve
action. The additives in an oil in combination with a certain gas may
sometimes lead to problems. This is usually unpredictable, but in
some cases, simply trying another oil has been successful.
Too much oil can be as undesirable as too little oil. The rate of
feed must be determined from experience and should be no more
than is necessary to properly lubricate a cylinder. Refer to Figure 3-5.
Too much lubrication of the discharge valves often causes carbon
build-up on the valve surfaces and becomes a flake-shaped impurity.
This affects the action of the valve and flakes breaking loose may
cause leakage in the subsequent stages.
• Corrosion can cause high localized stress and subsequent failure.
Springs are apt to fail first. The solution to corrosion problems is not
always simple, and is rarely inexpensive. Valve materials can be
changed. In some cases, properly sized scrubbers or chemical wash-
ers can eliminate or reduce contaminants before they enter the com-