Page 198 - Reciprocating Compressors Operation Maintenance

1 84 Reciprocating Compressors: Operation and Maintenance

of course, permit clearance and leakage. Wear on the sealing face of
the cup can prevent sealing of the rings against the cup, causing
leakage. Wear or damage of the cup may be caused by inadequate or
poor lubrication, corrosion, buildup of carbon, or abrasive material
in the gas.
* Damage to the piston in the form of scuffing or scoring can be a
source of leakage. If excessive wear has occurred on the rod, and
rings of the original diameter are used, leakage will occur.
* Improper assembly is a readily detectable source of leakage. Rings
installed improperly, that is, with the radial ring facing away from the
pressure, will allow the packing to leak. If the set has been assembled
in such a way that the packing cups are not perpendicular to the rod,
the packing rings will not be perpendicular to the rod and leakage
may occur.
* In these instances, leakage is actually a symptom rather than a root
cause; however, leakage can in itself become a problem. During
break-in, where a discrepancy may exist between the rings and the
rod due to expansion, blow-by can destroy the oil film and cause
excessive packing temperatures, causing further expansion and blow-
by. In this case, leakage is indeed the problem.

PACKING PROBLEMS

Some common problems associated with packing repairs in the field
are as follows:

1. Segment reversal. This term refers to the mismatching of the indi-
vidual ring segments. Rod packing segments are match-marked at
the factory in some manner to assure proper assembly. Improper
assembly of ring segments can result in excessive leakage and pre-
mature packing failure.
2. Mislocated packing. This term refers to having single-acting pack-
ing where double-acting packing should be installed.
3. Wrong side of packing facing pressure, A good rule of thumb to fol-
low is that the match marks on the individual packing segments
always face the pressure.
4. Break-in time. With engineered plastic packing, such as Teflon,
break-in time is about 20 to 30 minutes. However, with metallic