Page 295 - Reciprocating Compressors Operation Maintenance
P. 295
28O Reciprocating Compressors: Operation and Maintenance
design incorporated clearance between hubs. Figure 4-32 shows the outer
rirn under compression when the piston was tightened. This keeps the
joint tight. The new pistons were fabricated and installed, using the same
piston rings and piston rod. The breakage problem was eliminated.
Clearance
0.005 to
0.010 in.
20-in. one-piece 20-in. two-piece piston
piston has irregular has thin-walled ribbed
wall thickness dtie design with clearance
to core shift between hubs
FIGURE 4-32. One- and two-piece piston designs.
RENEWING PISTON RINGS
Piston rings must be replaced when the end gap (clearance) becomes
too great and blow-by of the gas occurs. End gap increases occur when:
• Rings become worn
• Cylinder bore wear takes place
• Scuffing occurs on the surface of the ring due to lack of lubrication,
or cylinder cooling is rendered ineffective, or the cylinder bore
becomes rough.
OVERSIZE PISTON RINGS
Oversize piston rings are required when the ring gap has tripled. Nor-
mally, the ring gap for a cast iron butt cut piston ring is .002" per inch of
