Page 202 - Reciprocating Compressors Operation Maintenance

I 88 Reciprocating Compressors: Operation and Maintenance

POSSIBLE
BREAK LINE

RING TYPES era BO
FIGURE 3-48. Packing ring damage caused by incorrect handling.

RATE OF LEAKAGE

Leakage amounts depend upon the amount of misfit between the rings
and the piston rod. Leakage can also be the result of disturbances along
the faces that must be in contact to form proper seals, as described for the
various ring styles. Under the best of circumstances, packings will weep
or bleed in small amounts that cannot be detected by ordinary means.
Some of this escape is due to separation at the various points of contact
as might be caused by vibration or temporary lubrication loss.
Also, some of this weeping is due to gas being forced into the rod
pores or into the lubrication film so that it escapes when the rod comes
out of the high pressure areas of its stroke into low pressure or atmos-
pheric conditions. These latter amounts are negligible and more serious
blow-by or gas loss will depend on the amount of disturbance at the
packing and sealing contours and faces.
It is possible, with additional cost beyond ordinary practice, to provide
packings of extreme accuracy, such as pre-lapped surfaces. In order for
this provision to be effective, it is also necessary to achieve perfect align-
ment and perfect case maintenance, particularly as to true and smooth
contacts. Moreover, the rod surfaces must be perfectly true and smooth.
If packings are allowed to leak excessively over long periods of time,
the destructive forces will progress to the point where they are difficult to
correct. New rings cannot be expected to perform satisfactorily if the
rods are tapered or scratched, and if the cases have also become damaged
in like manner. This would be similar to putting a new valve in an auto-
mobile engine without doing anything to its damaged seat.
Even after routine maintenance and replacement, adequate time must
be allowed for all of the sealing surfaces to mate or wear in. The packing