This case history shows how EDI "super-balanced" an integral engine/compressor to solve high vibration, severe oil leaks, slippage of composite chocks, and problems with the main bearing and crankshaft after an upgrade project. This is a summary of "Dynamic Design Considerations When Modernizing a Pipeline Compressor Station" EDI paper #81, which may be downloaded in its entirety.
Inertial Unbalance and Main Bearing Loads
An upgrade project involved increasing the speed and horsepower of a V14 engine with four 20.75" bore compressor cylinders on one side. The original configuration had no reciprocating balance weights ("dummy" crossheads) but did utilize four rotating counterweights to control the inertial unbalance.
Increasing the operating speed from 250 to 330 RPM caused the forces and moments to increase by the speed ratio squared. Using the nominal component weights, the OEM predicted that the forces were zero, but the moments would exceed their 350,000 ft-lb limit. Because these moments were considered too high, the addition of three "dummy crossheads" on the side of the engine opposite the compressor cylinders (Figure 7) was recommended. Note that these reciprocating weights were mounted directly to the frame, which is a fairly common configuration, but did not include any additional anchor bolts to the foundation.
The dummy crossheads act as reciprocating balance weights. The resultant inertial unbalance reported by the OEM with the dummy crossheads is listed in Table 3 and were reduced to below the recommended limit.
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