Page 194 - Reciprocating Compressors Operation Maintenance

I 80 Reciprocating Compressors: Operation and Maintenance

The metal back-up ring prevents extrusion and aids in removing
friction heat from the rod surface. The ring is bored a few thou-
sandths larger than the rod diameter, with zero clearance at the
joints to assure a tight gas seal.
6. Pressure Balance Set
The pressure balance ring set consists of a radial-cut packing ring
and a tangential seal ring (see Figure 3-43). The seal ring is fastened
directly to the packing ring with two screws in each segment. The
radial packing ring must always face the pressure side. These rings
are replaced only as a complete set.

GARTER SPRING

SEAL RING PACKING RING
FIGURE 3-43. Pressure balance set with seal ring fastened directly to the
packing ring (Source: C. Lee Cook, Louisville, Kentucky).

PACKING RING SIDE CLEARANCE

To ensure that the packing rings are full-floating under operating tem-
peratures, they must have proper side clearances. Side clearance is the
axial opening, or depth of the cup less the thickness of the rings that are
installed in the cup.
Table 3-9 shows the required side clearances for each cup depth and
ring material.
MAJOR SOURCES OF PACKING PROBLEMS

There are several indicators of "troubles with metallic packing" that
are frequently misunderstood and in reality are a manifestation of trouble
originating elsewhere.
Excessive or rapid wear is an example of this. Barring improper selec-
tion of mating materials or of materials and gas, excessive wear can be
caused by several factors. To fully understand and diagnose abnormal
wear, normal wear should be understood.