What are air compressor safety devices ?
Air Compressor Safety devices necessary for proper working of Air Compressor are following :-
1.Bursting discs are fitted on the cooler shells (At water side).
2.The Relief valves,which are fitted on discharge side for every stages.
3.Moisture drain valve (also called unloader),which are fitted at each cooler side.
4.Cooling water failure alarm.
5.Low L. O pressure alarm and trip.
6.Delivery air high temperature alarm on after cooler outlet (Max 93° C)
Before starting air compressor safety devices in brief we first know about air Compressor Normal Parameter.
What are the normal parameters of air compressor ?
LP discharge pressure of air compressor: 4 bars
HP discharge pressure of air compressor : 30 bars.
Intercooler inlet air temperature: 130 ° C
Intercooler outlet air temperature: 35 ° C
After cooler inlet air temperature: 130 ° C
After cooler outlet air temperature: 35 degree celcius
Air Compressor Safety devices uses and where it is fitted in Air compressor
Purpose of unloder valve (moisture drain valve) in air compressor ?
At starting of Air compressor,this valve must be opened,because this reduced the starting torque for the machine and also clear out any accumulated moisture and oil in the system.
Pressure relief valve
Relief valve releases excess pressure by opening the valves.
It opens at 10% over working pressure.
Valve lift of relief valve is proportional to the excess pressure build up.
Valve setting pressure of relief valve can be altered by spring tension.
Pressure is released by bursting the disc. It permanently damaged. It burst at setting pressure. Setting pressure cannot be altered in place.
When the temperature is high (above 105 °C), Pressure is released by melting (fusing) the metal.
And it cannot be used next time. ( because of permanently damage)
It did the work of Releasing all content or pressure to empty.
Where is the fusible plug fitted ?
Fusible plug is fitted between relief valve and air bottle under the side of the pipe.
Purpose :- It is fitted to release the compressed air in the event of abnormally high compressed air temperature.
● Fusible plug melt at 105 °C and release all content of air.
● It is made by 50% Bismuth, 30% tin, 20% lead.
● After the second stage cooler, a fusible plug is fitted to limit the temperature of the delivered air and thus protect the compressed air reservoirs and pipe work.
Air compressor safety devices
Can you fit the relief valve at the space of bursting disc and why ?
No,Because of their difference operation,Relief valve can not be fitted at the bursting disc in the compressor.
Bursting disc is fitted in air compressor for fully release and stop operation circuit.
Release valve opens excess pressure at compressor running and reseat at when pressure reduce or when the compressor is stopped.
As a result,cooling water can enter into compressed air space; which can cause water hammer when the next start of compressor.
At what condition fusible plug is fitted main air bottle ?
The fusible plug is fitted to the main air bottle when the relief valve is indirectly fitted to the air bottle. It can cause any obstruction by human error.
Purpose of bursting disc and where it is fitted ?
Bursting disc is fitted on each cooler shell of air compressor, which is used to give ample relief of pressure when cooler tubes burst.
Why bursting disc need to be annealed ?
Because of heating and time expanded, bursting disc is harden, so to get back the normal relief pressure it must be annealed.
Purpose of drain valve (Compressor and Air bottle)
It is process of removing the accumulation of oil water and sludge from the air bottle, scavenge space, intercooler compressor, and settling and service tank.
01) To drain the water and surplus oil in the air bottle.
02) To avoid air bottle corrosion.
03) Drain valve used to prevent staring air line explosion and sluggish & corrosions system valve.
Safety devices on main air bottle ?
Pressure relief valve.
Fusible plug (it is fitted ,when safety valve is not directly fitted on the bottle)
Low air pressure alarm.
Moisture drains valve.
I have added all important air compressor safety devices required for aur compressor used on ship.