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Premature Modulation

Premature Modulation

An area of savings in compressed air that is not usually addressed by the compressor manufacturer is that of compressor performance. Rotary screw compressors in particular are divided into two categories which are Modulating type and Load No Load type. Rotary screw "modulating type compressors" sometimes have a tendency to prematurely modulate. Modulating compressors have a small valve that controls the butterfly modulation or the inlet throttle. Often this valve if not adjusted properly can cause the compressor to malfunction or improper adjustment to these inlet controls means the compressor delivers less air than the normal rating. It is not surprising to see some compressors operating at 60% or less of their rated capacity. In order to get a firm handle on this problem, one has to test the compressor at different pressures in order to obtain a "performance print." Testing for a "performance print" will reveal at what pressure the throttle valve begins to close prematurely. Once the unit is isolated from service the test may take 20 -30 minutes with an Impact RM multi orifice LP meter to test the compressor performance in FAD (free air delivery) vs manufacturers rated capacity.