Page 93 - Reciprocating Compressors Operation Maintenance

8O Reciprocating Compressors: Operation and Maintenance

Press
Plunger
Hardwood
Block

Adjustable
Blocks

Teflon
Wearing
Ring
Polished
Hardwood
Mandrel
Piston

FIGURE 2-38. Assembly fixture for Teflon® wear rings (Source: Dresser-
Rand, Painted Post, New York).

PISTON RINGS

Piston rings made of PTFE will have an end gap clearance of .020" to
.024" per inch of piston diameter when fitted into the cylinder bore. Side
clearance in the groove should be 0.010"-0.020" per inch of width. It
should be remembered that Teflon expansion rates are approximately
seven times those of cast iron. Values for oil-lubricated compressors with
cast iron rings are .0035" per inch of diameter for the ring gap.
Figure 2-39 shows a piston for a non-lubricated compressor with a center
rider band that has pressure relief grooves and two piston rings installed.
Figure 2-40 shows a three-piece piston used in higher pressure, non-
lubricated process compressors handling synthesis gas. It consists of cast
iron ends with a cast iron piston ring carrier. The rider bands are sand-
wiched between the end pieces and the ring carrier.

AIR FILTRATION
j
Another area requiring special attention for successful trouble-free
operation of non-lubricated air compressors is proper filtration of the
incoming air.