The current version of Ariel's Reciprocating Compressor Performance Program calculates gas plus inertia loads at the crosshead pin. Inertia loads at the pin for pin load reversal calculations include the inertia of the piston and rod assembly, balance nut and crosshead with crosshead bushings.
All frames are rated in terms of internal gas rod load. Crosshead pin load reversal becomes important for small bore / high pressure double acting cylinders, single acting cylinders, and cylinder blow through conditions.
Gas plus inertia load will determine the load on the crosshead pin bearings and will define reversal at the crosshead pin for proper lubrication. Reversal is the change from a compression load to a tension load at the crosshead pin, thus allowing oil to flow into the loaded side of the bearings. Ariel recommends reversal for at least 30 degrees of crank rotation, with a reversal magnitude of 25% (the magnitude of the tension force must be 25% of the highest magnitude of the compression force and vice versa).
Ariel
Corporation Application Manual
7-Sept-2001