Page 293 - Reciprocating Compressors Operation Maintenance

278 Reciprocating Compressors: Operation and Maintenance

OVERSIZE PISTONS

Oversize compressor pistons are required when:

1, PistoE-to-cylinder bore clearance is too large to properly support rings.
2, Allowable piston rod runout cannot be obtained by adjustment of
crosshead shoes.
3, Clearance between bottom of piston rod and packing flange is less
than .015".

Table 4-6 shows the maximum allowable cylinder bore diameter before
oversize pistons are required.

PISTON FAILURES

Figure 4-31 explains typical compressor piston defects and failure
locations,

A. Piston mating surface fretting and wear on two-piece pistons.
B. Ring groove side wall wear.

TABLE 4-6
MAXIMUM ALLOWABLE CYLINDER BORE DIAMETER BEFORE
OVERSIZE PISTONS ARE REQUIRED

Maximum Bore Diameter Increase Allowed Before
Oversize Piston is Required
Cast Iron Aluminum All Piston Materials
Nominal Bore (Riding on (Riding on With Non-Metallic
Diameter, In. Bore), In. Bore), In. Rings & Riders, In.
3.99 .050 .050 .015
4.000-5.999 .075 .070 .015
6.000-7.999 .105 .085 .035
8.000-9.999 .125 .085 .040
10.000-14.999 .125 .085 .050
15.000-17.999 .125 .085 .050
18.000-22,499 .125 .085 .065
22.500-29.999 .125 .085 .085
30.000-34.999 .125 .085
35.000-42.000 .125 .085