Question

Q.1.

a) Write brief notes on how much air pressure is required to start any marine diesel main engine; how many times should the air reservoir be able to start. The conditions must be clearly stated.

b) What are the main causes of over pressurizing an air reservoir and what are the safety measures put in place?

c) What are the possible causes of an air compressor running for long periods to fill air reservoir on time?

Answer 1

A) the starting pressure should be provide enough speed to the piston during compression stroke for a quick combustion.

starting air pressure for both main and auxiliry engines should be between 25 to 42 bars.

the starting air reservoirs must provide 12 consecutive without replenishment and 6 consecutive for non- reversible engines.

B) poor pressure control on the machine

faulty pressure gauge

spring of discharge valve is malfunctioning

inter cooler air passege is chocked

second suction valve not closing properly

Safety measues

1. all component pipe, fitting,hoses must be rated for the maximum pressure of air compressor

2. relief valve automatically release air if tank pressure gets too high

3. shutoff valve should always in reach and visible

4. drain valves always kept away from moisture.

C) compressor requires constant maintenance and monitoring. compressor is an important machine in ship engine.

possible causes of an air compressor running for long periods to fill air reservoir on time>>

1. excessive vibration and noise

loose pulley, belt, cooler, flywheel

lack of oil in crankcase

piston hitting the valve plate

2. overheating of discharged air

damage in the head gasket

valves of 1st or 2nd stage leaking

decresed cooling water capacity

dirty or chocked intercooler tube

3.oil carry over in air

auto drain malfunctioning

oil water separator not working

4. low capacity compressor

leakage or fault in unloader

wrong setting of compressor

suction and discharge pipe leakage

5. milky oil in crank case

oil running hour is over

water leakage from jacket or cylinder liner.