Certain steps and systematic procedure need to be followed in order to start or stop an air compressor on a ship. In this article, we will learn how to start and stop an air compressor and also find out checks that are need to be made before starting the air compressor and also during its operation.
Checks before Starting the Air Compressor
The following steps are to be followed before starting an air compressor on a ship.
- Check the lube oil in the crankcase sump by means of dipstick or sight glass.
- All the valves of compressor discharge must be in normally open condition.
- If any manual valve is present in un-loader line, it must always be kept open.
- All alarms and trips- Lube oil low pressure, water high temperature, over load trip etc. must be checked for operation.
- All valves in cooling water line must be in normally open position.
- Cocks for all the pressure gauges must be in open position.
- Air intake filter should be clean.
- If compressor has not been started from long time than it should be turned on manually with a tommy-bar to check for the free movement of its parts.
Starting and Stopping procedure: What is Unloading the compressor?
Unloading is a normal procedure during the starting and stopping of the compressor. It is carried out due to following reasons:
- 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. 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.
- Air contains moisture and during the compression process some amount of moisture gets released. 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 un-loader comes in action and releases all the moisture accumulated inside the cylinder.
- Intermediate operation of un-loader is also selected so that during the process of compression any moisture or oil accumulation cannot take place inside it.
- 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 Compressor
- Check if all the pressure gauges are showing correct readings of lube oil pressure, water pressure etc.
- Check for any abnormal sound like knocking etc.
- Check for any lube oil or water leakages.
- If cylinder lubrication is provided, check the supply from sight glass.
- Check if the discharge pressure for all units is normal.
- Check air temperature after the final stage is under limit.
- Check the flow of cooling water from sight glass.
- If attached cooling water pump is provided check for its free rotation.
- Check the relief valve of all units for leakage. In some compressor, provision is given to check the relief valve with hand lever, if provided check all units.