Page 205 - Reciprocating Compressors Operation Maintenance

Operation and Maintenance of Reciprocating Compressors 191

Packing cups may adhere to cases due to the contact of lapped surfaces
and oil. Sharp tools such as chisels should not be used to separate the
cups because sealing surfaces can, of course, be damaged by nicks and
scratches, etc.
Packing is a precision component and should be treated as such.
When servicing and installing piston rod packing, the following points
must be closely observed to prevent packing failures:

1. The cups, rings, and piston rod must be clean.
2. The ring seating surfaces must be parallel with the face of the cup,
and cups must be parallel to each other.
3. The side clearance of the rings must be within the tolerances given
by the manufacturer. Sufficient end clearances must exist to permit
rings to seat properly against the piston rod.
4. The faces of the packing rings must be parallel. Tangent cut rings
must contact each other squarely to prevent leakage.
5. The bore of the packing rings should be no more than .002" larger
than the diameter of the rod. To prevent blow-by on starting, the
rings are frequently lapped to fit the rod.
6. Garter springs should be of the correct length and be free in their
grooves to give the packing the required pressure on the rod. If
they are worn or have lost their tension, replace them.
7. When assembling the packing on the rod, cleanliness is essential.
Dirt on the ring seating surface will stick to the rings. Dirt on the
faces of the cups will throw the packing case out of line and also
permit leakage between the cups.
8. Care must be taken to assemble the packing in the correct
sequence. If this is not done, the packing will not seal the pressure.
All ring segment ends are lettered or match-marked and must be
assembled accordingly.
9. The packing rings and the wearing faces of the packing case cup
should be coated with a small amount of clean lubricant at assem-
bly, except on non-lubricated packings.
10. The face of the pocket in which the packing case gasket rests must
be clean and free from burrs or scars to provide a flat seat for the
packing.
11. If the packing case gasket is solid copper or a triangle gasket used
previously, it should be annealed before using it a second time. It is
always preferable to use new gaskets.