Starting and Stopping procedure: Unloading the compressor:
Unloading is a normal procedure during the starting and stopping of the compressor. It is carried out due to the following reasons:
1. When starting a compressor motor, since the load on the motor is very high the starting current is also high. In order to avoid further loading of the compressor an un-loader arrangement is provided which is normally pneumatic or solenoid control and which releases the pressure during the starting of the compressor.
2. Once the current comes down to the running value, the un-loader closes automatically. Normally a timer function is used for opening and closing of un-loader.
3. Air contains moisture and during the compression process, some amount of moisture gets released. The liquid in any form is incompressible and if some amount of oily water mixture is present inside the cylinder then it will damage the compressor. To overcome this problem un-loader is used. During starting unloader comes into action and releases all the moisture accumulated inside the cylinder.
4. Intermediate operation of the un-loader is also selected so that during the process of compression any moisture or oil accumulation cannot take place inside it.
5. During stopping the compressor un-loader is operated so that for the next starting the cylinder will remain moisture-free.
Checks during the Operation of the Compressor
1. Check if all the pressure gauges are showing correct readings of lube oil pressure, water pressure, etc.
2. Check for any abnormal sounds like knocking etc.
3. Check for any lube oil or water leakages.
4. If cylinder lubrication is provided, check the supply from the sight glass.
5. Check if the discharge pressure for all units is normal.
6. Check the air temperature after the final stage is under the limit.
7. Check the flow of cooling water from the sight glass.
8. If the attached cooling water pump is provided check for its free rotation.
9. Check the relief valve of all units for leakage. In some compressors, provision is given to check the relief valve with a hand lever, if provided check all units.
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