Page 291 - Reciprocating Compressors Operation Maintenance

276 Reciprocating Compressors: Operation and Maintenance

Detailed inspection should be done when the compressor is overhauled
or whenever it is necessary to remove the piston and piston rod assembly
from the cylinder.
Caution: Before disassembly of a hollow piston from the piston rod,
check to see that there is no pressure trapped inside the piston. All hollow
pistons should be self-venting and a vent hole at the bottom of a ring
groove is included for this purpose. These vent holes should be checked
to be sure they are not plugged.
Detailed inspection of the piston includes:

* Cleaning piston completely including ring grooves of all carbon,
dirt, etc.
* Visually inspecting all portions for signs of scuffing, breakage of ring
lands, galling at hubs and piston nut washer seat, and cracking of any
component part.
* Dye-penetrant inspection of ribbing on two-piece pistons and of all
piston faces, particularly around the hub area.
* Complete dimensional check of piston OD, ID of piston rod boss,
piston ring grooves, and dimension of OD face and hub.
* Recording all dimensions and results of non-destructive testing
(NDT) inspection on appropriate forms.

Procedure for Inspection of Compressor Pistons

The following procedures should be followed when inspecting com-
pressor pistons.

1. Check piston in lathe or place in V-blocks, then indicate inside
diameter of piston boss.
2. Indicate counterbore or face of piston that bears against piston rod
collar or shoulder. This must be perpendicular with inside diameter
of the boss within .0005". If indication exceeds this amount,
machine counterbore or face until it indicates within .0005".
3. Indicate counterbore or face of piston where piston nut makes con-
tact. This must also be perpendicular to inside diameter of piston
boss within .0005". If not within this amount, machine face or coun-
terbore piston so that it does indicate within .0005".