Page 97 - Reciprocating Compressors Operation Maintenance

84 Reciprocating Compressors: Operation and Maintenance

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FIGURE 2-42. Piston rod deflection tendency during outward compression stroke.

ROD UNDER TENSION

As the piston discharges toward the crank end on the return stroke, as
seen in Figure 2-43, the net force of the suction and discharge pressures
results in a tension load on the rod. This is called rod load tension.
The operator can damage the compressor by decreasing the suction or
increasing the discharge pressure too far above the design pressures.

-*• Crank End

FIGURE 2-43. Piston rod stretch during compression in crank end portion of
cylinder.

ROD LOAD ASSIGNMENT

The rod can easily absorb most excessive tension and compressive
forces, but other parts, such as pistons, connecting rods and bolts,
crossheads and shoes, bushings and bearings, are also stressed. The most
highly stressed part, therefore, determines the rod load assigned by the