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Q6. i) Explain the term ‘Volumetric efficiency’ in respect of air compressors. (3)

ii) State reasons for drop in ‘Volumetric efficiency’ and how same can be restored? (7)

iii) Explain the purpose of ‘unloader’. Name the methods used for unloading, for ‘starting’ and ‘stopping’ when on automatic operation. (6)

Q4. Sketch and describe an Independent two-stage air compressor. Draw a set of typical Indicator diagrams and insert the various pressures and temperatures. Indicate the effect of a leaking H.P. suction valve and excessive H.P. clearance volume. (16)

Q6. Explain why each of the following features is considered desirable for air compressors:

(a) A single-throw crank for a multi-stage compressor; (4)

(b) Minimum clearance volume· (4)

(c) Multi tubular inter-stage cooler; (4)

(d) Generous size of suction filter.  (4)

Q8. i) Explain the basic theory of air compressors using a basic P-V cycle diagram, for a single stage air compressor, showing (a) adiabatic (b) polytropic (c) isothermal lines of compression. (6)

ii) Explain the advantages of multistage compression and intercooling. Superimpose the effects of both on the P-V diagram mentioned above. (6)

iii) Briefly explain bumping clearance. (4)

Q7. State the causes and remedial actions to be taken in case of the following occurring on an air compressor:

(a) Water mixed in the crankcase oil (4)

(b) LP safety valve blowing (4)

(c) Bursting disc rupture (4)

(d) Problems caused by detective piston rings (4)

Q5. (a) Name the safety devices fitted on 2 Stage air compressors on ships. Explain their functional purpose as well as location of fitment, using a schematic diagram. (12)

(b) State the maintenance and checks carried out periodically in order to keep them efficient. (4)

Q5. To achieve the optimum performance from a main air compressor, describe the routine maintenance necessary on the following components.

a) unloader. (4)

b) Air intake filter (4)

c) Suction/Discharge valves (4)

d) Intercoolers (4)

Q4. Describe what examination you will carry out on the following parts of Air Compressor,

a) Suction and delivery valves and seats. (4)

b) Relief valves and bursting discs. (4)

c) coolers and cooling passages. (4)

d) Piston and piston rings. (4)

Q5. a) Describe onboard main Air Compressor maintenance schedule. (8)

b) Describe malfunctions observed on Main Air Compressor. (8)

Q9) Explain the following:

(a) Control air dryer - working principle with diagram, of any one type of dryer of your choice (8)

(b) Any two types of Ballast water treatment system (8)

Q5. Sketch and describe an independent two-stage air compressor. Draw a set of typical indicator diagrams and insert the various pressures and temperatures. Indicate the effect of a leaking HP suction valve and excessive HP clearance volume (16)

Q3. Clean and dry control air is essential for efficient trouble-free operation of a ship’s pneumatic’ control air system.

a) Sketch and describe a low-pressure control air system used on board ships showing various arrangements to deal with dust oil and moisture as well as safety system. (8)

b) Explain using a line diagram, arrangements provided, to reduce the air pressure to 7/8 bars. Required for control air system. (8)