Page 311 - Reciprocating Compressors Operation Maintenance

296 Reciprocating Compressors: Operation and Maintenance

TABLE 4-8
PISTON NUT TORQUE VALUES

Thread Diameter Foot Pounds
(8TH.D.)
1" 200
\-V" 425
l
\- A" 775
i-r 1250
2" 1900
l
2- A" 2775
2-M" 3875
2-r 5200
r 6850

On large diameter piston rods, it is not practical to obtain the proper
torque and pre-stress of the rod by the use of torque wrenches. Here,
heaters to expand (lengthen) the rod are used that allow the nuts to be
easily turned the proper amount. Upon cooling, the rod "shrinks," setting
up the proper pre-stress which ensures tightness.
In all cases where a nut is used, it is locked to the piston rod by means
of a cotter pin. Piston rod lock nuts are usually the castellated style.

Torque Values For Crosshead Nuts

On those piston rods that use a nut tightened to the face of the
crosshead, it is important that the proper torque value be achieved to pre-
vent loosening or overstressing the rod.
Table 4-9 gives torque values for various size piston rod thread sizes at
the crosshead end.
Note: It is very important to properly block the crosshead to prevent it
from "cocking" when tightening the nut. Failure to take this precaution can
damage the crosshead pin bushing as well as the connecting rod bearing.
OTHER COMPRESSOR COMPONENT REPAIRS

As long as the proper methods and materials are used, all components
of the compressor may be successfully rebuilt or repaired.