pneumatically operated, automated unloaders. A mal-functioning unloader remains in an open position and thus reduces the capacity of the compressor. To identify this problem, proceed as follows:
• Set the compressor to run at a constant speed.
• Close the suspect unloader pocket and note the effect on the engine’s fuel gas manifold pressure.
• If the fuel gas manifold pressure did not increase, the unloader pocket did not really close, and it is probably broken.
Using this technique, I discovered that one end of the compressor’s two, double acting cylinders had a defective unloader. This failure reduced the capacity of the effected cylinder end by 40% and hence reduced the compressor’s capacity by 10%.
I had now accounted for 10% of the 28% missing horsepower I was searching for. My jacket, vest and tie were secure; but my slacks and dress shirt were well splattered with lube oil. And so, in my well-lubricated attire, I proceeded to take a temperature survey across the cylinders.