Air compressor : Importent Question and Answers Asked on Air Compressor
Important Questions and Answers Asked on Air compressor
1. What are the uses of compressed air on board ship?
Ans;-
a. To start the main propulsion engineb.To start Aux engine
c.For Automation & Instrumentation of various types of machinery
d.For Fire alarms e.For the operation of quick closing valves
- For the operation of pneumatic tools.
- For conducting aerobic breakdowns of the onboard sewage in a sewage plant.
- For pressure testing of different machinery parts, pipeline, etc
- For engine room general service
- For Deck general service
- For ships whistle
- For soot blowing of exhaust gas economizer
- For fresh & seawater hydrophores
- It is used in the lifeboat for heaving up the later if the air
- the motor is attached as a heaving provision.
2)Name the safety devices associated with 2 stages reciprocating air compressor.
Ans:-- Relief valve:
- Bursting disc on Intercooler (Waterside)
- Bursting disc & Fusible plug on aftercooler
- Moisture Drain valve
- Lube Oil low-pressure alarm and trip:
- Water high-temperature trip:
- Water no-flow trip:
- Motor Overload trip:
3)What is the volumetric efficiency of air compressors?
Ans;-- The actual volume of air drawn in / swept volume.
- Causes of reduced volumetric efficiency :
- Excessive Bumping c! earance~
- Defective (leaky) valves.
- Restrictions in the discharge lines.
- Restrictions in Intercooler & AftercooIer or reduced heat transfer.
- Clogged intake filter.
- Worn piston rings.
- Possible effects of leaky valves include :
- Reduction inefficiency,
- Increase in first stage pressure (due to leak in second stage suction).
- Drop-in first or second stage pressures ( due to leak in respective suction valves)
4 )InAir compressor, what is Bumping clearance? And why is it necessary?
Ans:-Bumping clearance is a term given to clearance between the piston and the cylinder cover, at the top end of the stroke.This is necessary to prevent mechanical contact between the moving piston and the-valves and gear.
State the reasons for an increase in Bumping clearances. And how can it be rectified?
The bumping c!clearance changes due to bearing wear down or due to piston crown wear, or even insufficient thickness of the gasket of the cylinder cover.
Adjustment is usually done by shim packs between the connecting rod and bottom-end bearing block or even between cylinder cover and block. 'With tandem type pistons, it is necessary to be able to adjust each stage separately (since the piston is common).
5)In Air compressor, how can Bumping clearance be checked?
Ans;- It can be checked, by inserting the lead gauge wire of known thickness, above the piston top. Now slowly turn the compressor over by hand. The thickness of the lead wire is now measured and should be around 1% of the cylinder bore (check the manual For the exact value)6)Explain the reasons for high carbon deposits on discharge valves.
Ans:-Oil passing the Piston rings gets oxidized at high temperature to form carbon deposits on discharge valves.Hence the reasons for carbon deposits are wearing down of piston rings & high temperatures due to insufficient cooling.
7) In Air compressor, what is the effect of leaky valves?
Ans:-- Reduced air delivery
- High air temperatures
- The increased running time of the compressor
- High backpressure from delivery line to air bottles.
8)Explain the necessity of intercoolers & after coolers with respect to air compressors
Ans:-1) Reduces compressor work hence saving in power by trying to approach Isothermal compression.
2) By inter -cooling the volume of air is reduced due to the reduction of temperature and hence the amount of air inlet after intercooler to next stage has increased which will also increase the amount of air discharge. Hence volumetric efficiency will increase.
3) Reduces the compressor size by reducing the volume of air delivered.
When we compare a compressor having inter-cooler to the one having no inter-cooler,
the compressor without intercooler will be bigger in size for the same output than the
compressor with intercooler.
4) It reduces air temperature.
Due to less temperature suction & delivery valves remain cleaner without being fouled
with carbonized oil.
5) It allows good lubrication of the compressor piston.
As we know for proper lubrication(cylinder & piston ring) to establish there must be optimum temperature if the temperature is high due to any reason, the lubrication will break which results in metal-to-metal contact and increases the wear.
6) Moisture separation is easier through intercooler drains.
As we are using atmospheric air to compress it and by default atmospheric air contains moisture which is harmful in many ways so every intercooler is fitted with drain valve. Moisture will get condensed when it comes in contact with cooling media and that will be drained by drain valve fitted in inter-cooler.
7) It also enables to deal with a greater weight of air for the same energy expended.
Due to the reduction in volume, the mass and the weight of air will increase for the next stage of compression.
9)What are the Solas requirement for Main Air Bottles?
Ans:-The total capacity of the air bottles should be sufficient to give at least 12 starts for reversible engine & 6 starts for the nonreversible engine without refilling the reservoirs
There must be 2 identical main air receivers & one emergency bottle for every vessel
10)What are the Air Bottle Mountings and Connections?
Ans:-The general mountings and connection present on-air bottle of a ship are:
Filling valve: This is a valve fitted in the supply connection from the main air compressor to the air bottle.
Outlet to the Main engine: An outlet valve and pipe are fitted for connection from the air bottle to the main engine for supplying air during starting.
Outlet to the auxiliary engine: An outlet valve and pipe are fitted for connection from air bottle to auxiliary engines for supplying air during starting.
Auxiliary connection: Other auxiliary supplies connections such as service air, safety air, etc. is also provided with an isolating valve.
Relief valve: A relief valve is fitted on the air bottle to relieve excess pressure inside the bottle.
Drain valve: A drain valve is fitted at the bottom of the bottle to drain accumulated condensate from the receiver.
Fusible plug: A fusible plug is fitted in the bottle with a separate connection leading out of the engine room so that in the event of a fire, this plug will melt and relieve all the air to the outside atmosphere. (Composition Bismuth 50%, Tin 30% & Lead 20%. Melting point 220F)
Manhole door: A manhole door is fitted in the bottle to carry out inspection of the same.
11)What are the air bottle safeties?
Ans:-1) Relief valve
2) Fusible plug
3) Drain
4) Low-pressure alarm
12)Explain the air bottle entry procedure
Ans:-- Inspection is to be carried out when the receiver capacity is not required for maneuvering
- Receiver properly isolated, pressurized, and notice pasted
- The internal pressure is to be checked by the pressure gauge and by opening the drain valved.
- Open the manhole door carefully and ventilate the air bottle
- Obtain an enclosed space permit and comply with it
- Ventilation is to be maintained during the entire time of enclosed space entry
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