Cylinder Blowby:
Occurs when discharge vapor passes around the piston during its upstroke, pressurizing the crankcase.
Symptoms:
Loss of efficiency.
Oil safety control tripping on low pressure or low oil pressure.
Motor overload tripping.
Compressor Internals Overview:
Components: Suction service valve, motor, crankcase (oil storage), oil pump, oil strainer, and oil check valve.
Oil Path:
Oil in the crankcase is pulled by the oil pump, lubricating load-bearing surfaces.
Oil then drains back to the crankcase through scavenger holes.
Diagnosing Blowby:
Compare crankcase and suction pressures.
Indication of Blowby:
If crankcase pressure is more than 3 psig above suction pressure, blowby is occurring.
Example: Crankcase pressure at 55 psig, suction pressure at 50 psig (5 psig difference).
Symptoms of Blowby:
Nuisance oil safety trips due to low oil in the crankcase.
Oil Level Observation:
Low oil level while the compressor is running, normal level when off.
Caused by the oil check valve not returning oil during operation.
Motor Overload Tripping:
Excessive oil in the motor area causes rotor drag, leading to overload tripping.
Testing for Blowby:
Use an access valve to compare crankcase and suction pressures.
Maximum Tolerance:
A pressure difference of 3 psig or less between crankcase and suction pressures is normal; more indicates blowby.
Common Causes:
Worn piston rings or valves.
Example Testing Procedure:
Measure crankcase pressure at the access valve.
Measure suction pressure at the suction service valve.
Compare the two readings.
No comments:
Post a Comment