Page 232 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

214 Major Process Equipment Maintenance and Repair

Figure 5-16. Typical nonlubricated crosshead diaphragm and compressor packing.

Inspect the piston rod for evidence of damage. If new packing rings are
to be installed, check the rod for wear and misalignment. All minor de-
fects in the surface of the rod should be removed by lapping. If the rod is
deeply scored, or if shoulders are present, the rod should be refinished or
replaced.
Inspect the surface of the cylinder head against which the packing
rests. It should be cleaned and free of defects.
Special size packings may be required for undersized rods.

Pressure Breaker Ring.The pressure breaker ring is sometimes used to
stabilize the pressure in the packing case during the suction and discharge
cycle. This prevents damage to packing rings and garter springs due to
the shock effect of the differential pressures involved.

Anti-Extruslon Rlngs. Since filled TFE components do not have the physi-
cal strength of their metallic counterparts, anti-extrusion rings are used
with TFE packing. Their primary purpose is to prevent, as a result of
pressure, the extrusion of the packing ring between the packing case and
piston rod. The metallic anti-extrusion ring also helps to dissipate heat
from the packing ring to the piston rod and packing cup.
The general practice is to allow .010 to .015 in. diametrical running
clearance between the anti-extrusion ring and the piston rod.