Compressors

Question 1

Fusible Plug

Answer 1

If it is possible to isolate the safety valve from the receiver (if it fitted on a manifold that can be isolated from the receiver) a fusible plug must be fitted to release pressure and discharge the receiver, in case of heating due to a fire in the vicinity.

This is done by the use of fusible plugs that are made from steel carrying a low melting point insert which will melt and then blow out leaving a clear hole.

The fusible alloy is an alloy of lead, bismuth and antimony. The melting temperature is approximately 150OC. The connection must be made to discharge the receiver contents in a safe manner, such as to the bilge.
Air receivers used to control remotely operated valves must be fitted with safety valves, not fusible plugs.

Question 2

Fittings on a air receiver

Answer 2

Seating
The air receiver seating and securing straps.
Information plate
This plate gives details about the construction of the air receiver, such as its individual identification number; date of construction and hydraulic test; working pressure etc.
Filling valve
The air receiver filling line from the compressor, and isolation valve. This filling line must be a dedicated line, with nothing else being supplied from it.
Compressor start/stop pressure-stats
Connections to pressure-stats to automatically start and stop the air compressor(s) are fitted. The low pressure-stat will start the compressor when the air receiver pressure is low, and the high pressure-stat will stop the compressor when the air receiver is up to normal pressure.
Distribution to consumer valves
The air start line to main engines commonly has its own distribution isolation valve. Other consumers may have their own distribution valves fitted directly onto the air receiver, or onto a common distribution manifold.
Drain valve(s)
Drain valves are fitted to allow the regular discharge of any condensate or oil that may be carried over from the compressor. In upright receivers one drain is sufficient at the lowest point, but in receivers mounted horizontally a drain valve at both ends is essential so that the receiver can be purged at whatever attitude the vessel is in. The drains must discharge through a pipe to a safe place, usually the tank tops in the bilge. The drain should be of sufficient size to prevent choking.

Pressure gauge(s)
A pressure gauge must be fitted to the receiver. This gauge must have a means by which it can be closed off from the receiver so that a faulty gauge can be tested and/or changed. There may also be a separate remote pressure gauge fitted.
Safety valve
A safety valve is fitted to the receiver so that the receiver cannot be charged beyond its safe working pressure. The safety valve must be set to relieve the receiver of excessive pressure rise and must have sufficient area to prevent accumulation of pressure for any reason. The safety valve is set to working pressure + 10%.
Fusible plug
Manhole door

All stop valves should be slow-opening valves to prevent sudden build-up of pressure when connecting any pipe system.

Question 3

With reference to main air receivers list four safety features stating the purpose of each
state the pressure that a pressure relief valve should lift

Answer 3

Safety devices associated with the compressed air system, safety valves, fusible
plugs, compressor bursting discs, compressor lifting heads