Crankcase Seal Repairs
Crankcase Seal Repairs
There are several types of crankcase seals, depending on the manufacturer. On reciprocating compressors, the crankshaft extends through the compressor housing to provide a mount for the pulley wheel or flexible coupling. Now the shaft must be sealed to prevent leakage of lubricating oil and refrigerant. The crankshaft seal is bathed in lubricating oil at a pressure equal to the suction pressure of the refrigerant. The first indication of crankshaft seal failure is excessive oil leaking at the shaft
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When the seal must be replaced or when it shows signs of abnormal wear or damage to the running surfaces, a definite reason can be found for the abnormal conditions. Make an inspection to locate and correct the trouble, or the failure will recur.
Seal failure is very often caused by faulty lubrication, usually because of the condition of the crankcase oil. A dirty or broken oil seal is generally caused by one or both of the following conditions:
- Dirt or foreign material is in the system or system piping. Dirt frequently enters the system at the time of installation. After a period of operation, foreign material will accumulate in the compressor crankcase, tending to concentrate in the oil chamber surrounding the shaft seal. When the oil contains grit, it is only a matter of time until the highly finished running faces become damaged, causing failure of the shaft seal.
- Moisture is frequently the cause of an acid condition of the lubricating oil. Oil in this condition will not provide satisfactory lubrication and will cause failure of the compressor parts. Use a refrigerant dehydrator when the compressor is put into operation if you suspect that moisture may be a problem. Anytime foreign material is found in the lubricating oil, thoroughly clean the entire system (piping, valves, and strainers).
REMOVING A SHAFT SEAL
.—If a shaft seal must be removed, proceed as follows:
If the seal is broken to the extent that it permits excessive oil leakage, do NOT attempt to pump the refrigerant out of the compressor. If you do, air containing moisture will be drawn into the system through the damaged seal. Moisture entering the refrigerant system may cause expansion valves to freeze. This can cause acid formation and other problems. If oil is leaking excessively, close the compressor suction and discharge valves and relieve the pressure to the atmosphere by loosening a connection on the compressor discharge gauge line.
Next, drain the oil from the compressor crankcase. Since the oil contains refrigerant, it will foam while being drained. Leave the oil dram valve or plug open while you are working on the seal. This ensures that refrigerant escaping from the oil remaining in the crankcase will not build up pressure and blow out the seal while it is being removed.
Remove the compressor flywheel (or coupling) and carefully remove the shaft seal assembly. If the assembly cannot be readily removed, build up a slight pressure in the compressor crankcase. To do this, slightly open the compressor suction valve. Take the necessary precautions to support the seal and to prevent it from being blown from the compressor and damaged.
INSTALLING A SHAFT SEAL.
—Clean and replace the entire seal assembly according to the manufacturer’s instructions.
Wipe the shaft clean with a linen or silk cloth; do not use a dirty or lint-bearing cloth. Be careful not to touch the bearing surfaces with your hands as you unwrap the seal. Rinse the seal in an approved solvent and allow it to air-dry. (Do NOT wipe the seal dry!) Dip the seal in clean refrigerant oil. Follow the instructions found in the manufacturer’s technical manual to insert the assembly. Bolt the seal cover in place and tighten the bolts evenly. Replace the flywheel and belts or coupling and check and correct the motor and compressor shaft alignment. To test the unit for leaks, open the suction and discharge valves and use a halide leak detector.
