Page 95 - Reciprocating Compressors Operation Maintenance

82 Reciprocating Compressors: Operation and Maintenance

Filter cartridge efficiency should be 99.7% for 10 micron particles,
and 95% for 5 micron particles.
Suction piping from the filter to the cylinder should be clean and free
of dust and scale. Steel piping should be treated with a rust inhibiting or
epoxy paint. In critical applications, stainless steel or aluminum piping
should be used. These materials are always preferred.
Abrasive materials can become embedded in the Teflon and will be
retained, shortening ring life and accelerating cylinder wear. Thus the
cost of maintenance will increase if air filtration is inadequate.

VALVES AND UNLOADERS

Valves, unloaders, and clearance pockets for non-lube units have
teflon nubs or bushings for self-lubricating operation. Channel valves
have teflon strips over the channels and Teflon guides at the ends. Plate
valves usually have Teflon nubs between the springs and the plate. In
some cases, all components are Teflon coated.
Unloaders have Teflon bushings in the sliding parts (Figure 2-41).

PISTON ROD COLUMN OR FRAME LOADING

Each compressor is subject to a piston rod column or frame load limi-
tation. The size of each compressor establishes a maximum allowable
frame or piston rod column load. Keeping within this allowable load
ensures that the frame castings and running gear parts, such as crankpins,
crosshead pins, main bearings, crossheads, and connecting rods are not
subject to loadings or stresses beyond their design points.
Piston rod column or frame load is the force that the pressure in a
cylinder exerts on the piston and, in turn, the piston exerts on the piston
rod. This load is transmitted through the piston rod back to the frame and
running gear parts.
Frame load is the difference of the total loads across the piston or
across one cylinder. It is the net area of the piston times the difference
between the discharge and suction pressures for that cylinder,

EXCESSIVE ROD LOAD

Most major damage to compressors is caused by exceeding recom-
mended rod loads. For this reason, it is important that operators and
mechanics understand rod loads before they start a compressor.