Page 206 - Reciprocating Compressors Operation Maintenance

1 92 Reciprocating Compressors: Operation and Maintenance

12. When installing the packing case and gasket, care should be taken
in tightening nuts on the packing case studs. These should be tight-
ened evenly to keep the bore of the packing case centered on the
piston rod. This can be checked at various times when tightening
the packing case stud nuts by means of feelers between the bore of
the packing case and the rod. After the case has been installed, the
clearance between the rod and the bore of the packing case should
be checked with the compressor piston at both ends and in the cen-
ter of its stroke.
13. After installing the packing case, connect the lube oil and vent
lines and fill the oil line by venting and operating the lubricator.

PISTON MOD OIL WIPER PACKING

The stuffer in the frame head of the cylinder housing or crosshead
guide contains a set of piston rod oil scraper rings and a gland (see Fig-
ure 3-51) that prevents crankcase oil from being carried out of the
crankcase along the rod.
A typical gland is designed to allow no more than .005'" total side
clearance for the scraper rings, generally .002" to .003". If the clearance
is insufficient for the rings to float on the rod, they will not function
properly. Too much clearance will cause the rings to act as a pump
instead of wiping oil from the rod.
Care must be taken to maintain a smooth rod surface. Nicks or dents in
the rings or scores on the rod will prevent a tight seal.
If, after considerable service, the rings should start leaking oil, examine
them. If the ends butt together, the rings should be replaced with new ones.
Renewal oil scraper rings are furnished in sets of two. These segments
are lettered, and adjacent segments should match.

COMPRESSOR CONTROL SYSTEMS i

Installation and start-up procedures, troubleshooting, and maintenance
are important to a successful compressor installation. Of equal impor-
tance is the subject of capacity control
Compressor capacity control is the method by which the output of a
compressor is regulated to provide, as nearly as possible, only that
amount of air or gas required at a particular instant. The ideal governing