Page 187 - Reciprocating Compressors Operation Maintenance

Operation and Maintenance of Reciprocating Compressors 173

In addition to the normal vent to the atmosphere, packing cases may be
arranged to vent higher pressure or introduce pressure between any of the
individual rings. This is done generally to control leakage or provide means
for recovering leaked gas. For cases vented as shown in Figure 3-33, normal
uses include preventing air leakage into the cylinder when suction pressure
is below atmospheric pressures or maintaining zero leakage of a dangerous
or expensive gas.

ALL LEAKAGE TO VENT
ZERO LEAKAGE TO ATMOSPHERE
BUFFERED VENT ARRANGEMENT

GAS SUPPLY AT
ABOVE ATMOSPHERIC
PRESSURE

GAS LEAKAGE ONLY
NO AIR TO CYLINDER
VACUUM PACKING
FIGURE 3-33. Special venting provisions on packing cases. (Source: C. Lee
Cook, Louisville, Kentucky).

Vented packing cases can also be fitted with an effective standstill seal
"Static-Pac"™ (see Figure 3-34).
In normal compressor operation, the minimum pressure that will exist
in the cylinder, and consequently, to which the packing will be subjected,
discounting variations due to valve function, will be equal to the suction
pressure. The differential pressure across the packing will fluctuate