In this instance, as its a compressor, there are two devices that enable the motor start without load….
There is the non-return valve on the compressore discharge/inlet to the receiver, this prevents air leaking back into the cylinder. Then there is the pressure switch assembly that incorporates a valve that vents the compressor discharge line once the switch reaches its set pressure…basically it allows the air discharging from the compressor but upstream of the nrv, to be vented to atmosphere…
The combination of both allow the motor to start without load….
Edited By John Rudd on 31/10/2016 19:34:30