OVERHAUL OF MAIN AIR COMPRESSOR VALVES (PLATE TYPE) AND TESTING

Procedure for overhauling the plate-type compressor valves

1. Preparation: Stop the air compressor, isolate the air and cooling water, drain the intercooler/ aftercooler, and relieve the pressure. Obtain the maker's manual and the correct spares (valve plates, springs, seats, gaskets).
2. Remove the valve assemblies: Remove the valve covers/ caps and withdraw the suction and discharge valve assemblies (the plate-type valves) from the cylinder head/ valve pockets. Mark each valve and its position.
3. Dismantle the valve: Disassemble the valve - remove the valve plate(s), springs, and the valve seat/ guard. Note the arrangement and the number/ position of the springs.
4. Clean all parts: Clean the valve plate, seat, springs and body using an appropriate solvent; remove carbon, oil and deposits. Do not damage the lapped/ sealing faces.
5. Inspect each part:

• Valve plate: for wear, pitting, scoring, cracking, distortion and breakage; check the sealing face is flat and smooth.
• Valve seat: for wear, pitting, scoring and damage to the sealing face; check it is flat.
• Springs: for breakage, fatigue, loss of tension and corrosion; check the free length.
• Valve body/ guard: for cracks, wear and damage.
• Gaskets/ O-rings: for deterioration and damage.

1. Renew as necessary: Replace worn/ damaged valve plates, springs, seats and gaskets with genuine spares. The valve plate and seat are often renewed together (matched).
2. Reassemble the valve: Fit the new/ reconditioned parts in the correct order - the valve plate, springs and seat/ guard - ensuring the springs are correctly seated and the plate moves freely. Check the valve lifts correctly.
3. Refit the valve assemblies: Fit the valve assemblies into the cylinder head/ valve pockets with new gaskets, and refit the covers/ caps, torquing to specification.
4. Reconnect the air and cooling water, and test (see below).

Parts requiring close attention:

• The valve plate and seat sealing faces (must be flat, smooth and free of damage for a good seal).
• The springs (correct tension, no breakage).
• The valve plate lift/ travel (correct clearance).
• The gaskets/ O-rings (must be renewed to prevent leaks).
• The cleanliness of the valve pockets and the air passages.

Testing of the compressor valves

1. Leak/ seat test: With the valve assembled, test the valve for leakage - the valve plate should seat and seal (no air/ liquid passing when the valve is closed). This can be done by applying air/ pressure to one side and checking for leakage, or by a leak test on the valve.
2. Lift/ operation test: Check the valve plate lifts freely and returns to seat (no sticking).
3. Compressor test: After refitting, run the compressor and check the interstage/ discharge pressures, the air delivery, and the valve operation (no abnormal noise, no overheating). Confirm the compressor reaches the correct pressure and delivers the rated capacity.
4. Check for leaks: Check the valve covers/ gaskets for air leaks during the run.