A refrigeration system is the back bone of a reefer ships. So, safety of this system is very essential on ships.
There are the following safety devices fitted in the refrigeration system of ships:
- LP cut-out switch: This is a compressor safety device that cut-off the compressor when there is a pressure drop in the suction pipe. This is set at a pressure corresponding to 5°C below the lowest expected evaporating gauge reading.
- HP cut-out switch: This is also a compressor safety device in which the high-pressure cut-out activates and trips the compressor when the discharge side pressure increases above the limit value.Set at a pressure corresponding to 5°C above the highest expected condensing gauge reading.
- Lub Oil LP cut-out: This safety is again for the compressor as it is the only machinery in the circuit having rotational parts which require continuous lubrication. Oil pressure usually set at 2 bar above crankcase pressure.
- Condenser cooling water LP cut-out:
- Liquid shock valve on Compressor: It is fitted on the cylinder head of the compressor to prevent the shock due to liquid entering the compressor.
- Bursting disc on the cylinder head, between inlet and discharge manifold.
- Bursting disc on Condenser, [if fitted]
- The relief valve on Condenser: It is fitted on the condenser refrigerant line and is used to avoid damage to the condenser if there is high pressure in the discharge line.
- Master solenoid valve: It fitted in the common or mainline after the condenser discharge. It closes when the compressor stops or trips to avoid overflow of refrigerant into the evaporator. It is used to prevent liquid from being entered into Compressor, when the plant is standstill, especially in Large Plant.
- Oil Heater: It is provided for the compressor crankcase oil and prevents the compressor from getting excessively cold which may affect the lubrication of the parts.
You may also like to read: Vapour Refrigeration Cycle
References: Marine Aux Machinery by H.D.McGeorge, MarineInsight.com