- Bumping clearance is the clearance between the top of the piston and the cylinder head when the piston is in T.D.C.
- This is clearance should be checked on ever overhaul and should be within limits specified in the manual
Too less a clearance
- Posses a risk of the piston hitting the cylinder which may lead to dangerous mechanical failure.
- Turn the compressor manually prior running to ensure no mechanical resistance to the piston
Too large a clearance
- less air is drawn in the suction side as it retards the formation of vacuum due to large clearance
- drop the volumetric efficiency
- longer run time
Measurement of clearance
- Place a lead ball or a lead wire on top of the piston
- Turn the compressor by hand
- Measure the thickness of lead wire using a vernier caliper
- Compare with manufacturer manual
- Adjust if required
Reason for change in clearance
- Increase in clearance can be due to wear in bottom end bearing
- Using wrong gaskets on the head can reduce the clearance
Precaution
- Use only original and genuine spare parts from the manufacturer
- Check size of the gasket used in every overhaul
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