The usual method of unloading a low pressure air compressor at start-up is accomplished by __________.

Correct Answer: Option C — holding the suction valve open

Unloading a compressor during start-up reduces the starting torque required by the prime mover. Holding the suction valve open prevents the cylinder from drawing in air, effectively bypassing the compression cycle and allowing the motor to reach operating speed without fighting the resistance of a pressurized discharge system.