What could be said about compressor condition if it's running current deviates from normal?
For equipment driven by an electric motor, such as compressors and pumps, the running current of a driving motor is good evaluation criteria for the overall unit condition.
1. Electric motor power (current) increased
a) Possible failure of the inlet/discharge (sticking) valve, the discharge pressure (especially of an intermediate stage) increases and compression ratio increases.
Check the inlet/discharge valve of each stage and repair or replace.b) Seizure of bearing, deterioration of grease or leakage.
Repair or replace the bearing.c) Seizure of piston.
Check liner, rings and piston for wear, tear any other abnormalities.
2. Electric motor power (current) decreases
a) Failure of inlet/discharge valve (damaged).
Volume efficiency decreases and as a result, air volume is reduced. 
Accompanied by the increased temperature of the stage as hot compressed air from the next stage leaks back. Check inlet/discharge valve and repair or replace.b) Stage 1 inlet valve is stuck, thin air in sucked, discharge pressure is reduced, and air volume is reduced. Check the inlet/discharge valve and repair or replace
c) Inlet filter/silencer is abnormally contaminated. Clean or replace the inlet silencer.
d) Worn or damaged piston rings. Air leakage increases, thus reducing volume efficiency and also compression ratio. Overhaul compressor, replace the piston rings.
