Page 307 - Reciprocating Compressors Operation Maintenance

292 Reciprocating Compressors: Operation and Maintenance

RECONDITIONING OF COMPRESSOR PISTON RODS

If a rod is scratched, nicked, worn, or a slight shoulder exists, it is pos-
sible to recondition. If previous inspection has revealed any indication of
cracks, inclusions, or imperfections in material, the rod must be
scrapped.
Note: Do not attempt to weld piston rods,

Regrinding

Piston rods may be ground undersize, and the standard packing rings
can be used. Generally .002"-.003" per inch of piston rod diameter can
be ground for medium pressures, but as the operating pressure increases
above 1000 psi, this should be limited to a total of .003" under the nomi-
nal piston rod size.
On low pressure air service (125 psi), as much as .020" has been
removed and standard packing used. However, it is better practice to
grind undersize and return to standard nominal size by one of several
methods to be discussed next. Generally, with an undersized rod, the
packing rings will take longer to break in and the leakage will be greater
during the break-in period.

Metal Spray

Metal spray application is an acceptable reconditioning technique on
piston rods used in pressures up to 400 psi. After proper cleaning and
surface preparation, the rod may be sprayed with 420 stainless steel,
which is equivalent to 413 SS. The rod is ground to normal size after
spray. Surface finish should be as shown earlier.

Plasma Spray

Development of plasma spray and suitable coatings allow piston rods
not only to be reconditioned but to be given a surface treatment superior
to that originally on the rod. Overlays of tungsten carbide and chrome
oxide can give the piston rod longer wear life. Care must be taken to
check the rod for straightness after spraying. Plasma spray has superior