If the pump unit appears to turn freely then the following should be checked:
- Check condition of the air filter. Blockage in the filter element will adversely affect compressor performance.
- Check for blown head gasket. This is demonstrated by oil leakage from the gasket under the compressor head. Priming performance will be adversely affected. Remove and replace the head gasket as required.
- Listen to the harmonic tone of compressor. If compressor sounds irregular in its action then a worn / unseated / broken valve is likely. This will require a compressor rebuild or compressor replacement. Further testing should be carried out to decide this (see bottom of this section).
- Check If Pop-Off valve is releasing. A banging sound results from too much compressed air being produced. Likely causes are:
- A restriction in airflow ‘downstream’ of the compressor - check inline air check valve first for correct operation.
- Incorrect jets and nozzles fitted.
- Defective pop - off valve. Standard units are set to 125 psi. DO NOT fit a higher working pressure valve - this is potentially very dangerous.
- Engine / motor overspeed. (Normal engine operating speed is 2000 rpm).
- Wrong pulleys / belts resulting in the compressor being driven overspeed (see reference chart in the appendices)
Test your compressor:
- Install 120 psi Pressure Gauge In Compressed Air System
- Using a tee and reducer, fit the gauge in the line and run the pump.
- Optimal pressure is around 60 psi (+/- 10 psi).
- Higher pressure indicates a restriction in the priming system.
- Lower pressure indicates a defective compressor or badly worn venturi jet / nozzle.
Other Compressor Checks
- Inspect belts for excessive wear and damage.
- Repair / replace as required.
Belt Tension: Reasonable belt tension is set on the free travel in the belt between the two pulleys. Belt adjustment depends on the belt fitted:
- Black toothed belt. The compressor is raised (therefore tensioning the belt) by adding paper gaskets to the base of the unit. ½” deflection is optimal.
- Orange segmented belt. To carry out adjustment of belt tension remove one link, refit and check tension. Continue this process until the correct tension is achieved. Fit around drive pulley and then put it over the driven pulley and turn the unit over. ½” - 1” deflection is optimal.
- Double ‘Vee belt’ Drives (Quincy compressors). Adjust using the idler pulley. 2” deflection is optimal.
- Pay particular attention to oil leaks from the Bendix base gaskets, as the unit is on a common supply from the Diesel engine and rapid oil loss can occur.
- Ensure that oil pump gauge is not jammed or damaged.
- Excessive bouncing of the needle indicates excessive wear in the pump.
- Repair / fix oil leaks as required.