Engine Room Auxiliaries (MEP) — Most Asked Questions
24 questions asked about engine room auxiliaries (mep) across the General and Fn 3 and Fn 6 and Fn 4b papers, heaviest first. 1 of them are must-master.
Learn the system first
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1 Safeties of main air compressor?
Answer
Each compressor stage breathes through a filter and blows through its own relief valve, with bursting discs guarding the cooler water sides.
- Suction filter on the intake; a relief valve after the discharge of every stage lifts if stage pressure exceeds design.
- Bursting discs on the water side of intercooler and aftercooler: air inside tubes, water outside — a burst tube vents to the disc instead of pressurising the jacket.
- Unloader (moisture-drain) valve opened at starting: cuts starting torque and clears accumulated moisture and oil from the system.
- Watch the rest: cooling-water flow, lube-oil level and pressure, discharge temperature, and slow or late valves — excess suction-valve lift wrecks volumetric efficiency and breaks valves.
Surveyor follow-up: second-stage relief valve lifts continuously while first-stage pressure is normal — which valve has failed?
Full theory: Air Compressor Safety — Relief Devices, Receivers & SOLAS -
2 Recording transfer of oil on board ship or its discharge and the discharge of oily-bilge or ballast overboard
Answer
Every oil move goes in the Oil Record Book Part 1 by code: ballast, dirty water, bilge, overboard, failures, accidents and bunkering.
- Code A: ballasting or cleaning fuel tanks; Code B: discharging dirty ballast or cleaning water with ship positions.
- Codes C to E: collecting bilge to slop tank, then overboard through the separator with start, stop and 15 ppm proof.
- Codes F and G: separator failure and accidental discharge with times, causes and remedies.
- Code H: bunkering with quantities and connections; every entry tank-to-tank, signed by officer and master.
Surveyor follow-up: internal transfer between fuel tanks only — log it or skip it, and under which code?
Full theory: When You May Discharge — MARPOL Annex I Limits, Distances and Special Areas -
3 Air compressor safty
Also asked: “air compreser safety”, “Safety in compresor”
Answer
Compressor safeties guard pressure, heat and oil: relief after every stage, discs and plugs on heat, trip on low oil.
- Relief valve after every stage with lifting pressure rising stage by stage.
- Copper bursting disc on the air side and fusible plug on the hot discharge against over-pressure and over-temperature.
- Low lube-oil pressure alarm and trip — running dry wrecks the machine in minutes.
- Suction filters oil-free, receivers on non-returns, and drains blown daily so the first start never hammers wet.
Surveyor follow-up: second-stage relief lifting with first-stage normal — which valves have failed?
Full theory: Air Compressor Safety — Relief Devices, Receivers & SOLAS -
4 Safeties in air compressor Working of fusible plug
Answer
Compressor safeties pair pressure with temperature: relief valves and discs vent pressure, the fusible plug melts on heat.
- Relief valve after every stage with lifting pressure rising stage by stage.
- Copper bursting disc on the air side bursts past its set pressure to save the manifold.
- Fusible plug on the hot discharge melts near 105 degrees — bismuth, tin and lead alloy — dumping air before reservoirs cook.
- Low oil-pressure alarm and trip behind them; suction filters oil-free with drains blown daily.
Surveyor follow-up: plug melted with pressures normal — heat, oil or cooling water, and what do you check first?
Full theory: Air Compressor Safety — Relief Devices, Receivers & SOLAS -
5 Air compressor manual start procedure
Also asked: “Manual starting of air compressor”, “Air Compressor details starting procedure”
Answer
Start compressors unloaded and dry: drains open, valves lined, short purge run, then close up and load.
- Open all drains for an unloaded start with moisture purged as she turns over.
- Close drains after the short purge interval and let unloaders cut out for loaded running.
- Unload by suction throttling, speed control, suction-plate depressors, discharge bypass or stepped cylinders.
- Prove pressures stage by stage with reliefs, temperatures and oil proved before leaving her loaded.
Surveyor follow-up: starts loaded with drains shut — unloader, procedure or drains, and what breaks first?
Full theory: Air Compressor Operations — Lubrication, Drains & Running -
6 Air compressor overhauling
Answer
Overhaul compressors from valves down: heads off, valves lapped, rings gapped, clearances proved, reliefs bench-tested.
- Lift heads, pull suction and discharge valves with rods, pins and rings laid in order.
- Soak valves in clean oil, lap seats, renew rings with butt and axial gaps to maker figures.
- Prove pistons, liners and bearings with clearances logged; hydraulically test reliefs to lift.
- Rebuild torqued with oil, cooling and drains proved — first start unloaded with drains open.
Surveyor follow-up: delivery pressure low after overhaul with timing correct — rings, valves or clearances?
Full theory: Air Compressor Maintenance — Lapping, Clearances & Overhaul -
7 bumping clearance value of air compressor
Answer
Bumping clearance is the piston-to-head gap at top dead centre: smallest safe gap for efficiency without mechanical kiss.
- Set by head-gasket thickness and shims between rod foot and bottom-end bearing.
- Too much clearance re-expands trapped air, heats delivery and kills volumetric efficiency.
- Too little risks piston striking the head, especially unloaded at start and stop.
- Wear-down of main bearings grows the gap — re-shim to maker figures on schedule.
Surveyor follow-up: delivery hot with clearance double the book — gasket, shims or bearings, and what first?
Full theory: Air Compressor Operations — Lubrication, Drains & Running -
8 Packing used for fresh water
Also asked: “Packing used for sea water”
Answer
Pack for the medium: soft non-corrosive packing for fresh water, bronze-fitted glands for sea water — iron never meets salt.
- Fresh-water pumps run cast-iron casings with standard soft packing and stainless shafts.
- Sea-water pumps upgrade to gunmetal casings, aluminium-bronze impellers and leaded-bronze rings against corrosion.
- Match packing to temperature, viscosity and chemistry — cavitation from hot suction kills any packing fast.
- Prove by weep rate and temperature: dry glands cook, flooded glands wash out — steady drip wins.
Surveyor follow-up: cast-iron sea-water pump with fresh-water packing fitted — material, packing or suction first to fail?
Full theory: Centrifugal Pump Construction -
9 Bilge injection pre and after test checks
Answer
Bilge injection is the emergency sea-to-engine-room valve: prove shut and tight daily, ready to flood the bilge on order.
- Shut and lashed with handwheel proved free, non-return seating tight and overboard discharge lined up first.
- Open sea injection slowly on order, watching bilge level fall with pump suction proved and strainers clear.
- After the test shut, drain and re-lash the valve with the bilge pumped back to normal working level.
- Log date, time, level change and valve condition — an unlogged injection valve is an unproved one.
Surveyor follow-up: injection valve weeping with the pump losing suction after the drill — seating, strainer or air leak first?
Full theory: The Bilge System the Separator Serves -
10 Air compressor bursting disc burst during maneov
Answer
A bursting disc that lets go in manoeuvring is a temperature story: stopping the engine left the compressor without its cooling water or its load.
- The disc protects the cooler and the air path from overpressure caused by high delivery temperature, not by a system fault.
- On stopping the engine, cooling water to the compressor must continue for the maker’s stated cooling-down period.
- Cut the cooling during a manoeuvring and the trapped air heats, pressure rises, and the disc releases as designed.
- Replace the disc with the correct rating, prove the cooling timer, and check the delivery temperature alarm and trip.
Surveyor follow-up: second disc burst in a month with delivery temperature normal — is the disc rating, the water or the outlet the cause?
Full theory: Air Compressor Maintenance — Lapping, Clearances & Overhaul -
11 Air compressor efficienc
Answer
Compressor efficiency is volume over mass: how much air a given power actually puts into the receiver.
- Volumetric efficiency is the volume drawn in against the swept volume — clearances, valves and rebreathing all reduce it.
- Isothermal efficiency compares the theoretical work of compression with the work actually put in.
- Clearance volume, valve losses and the after-cooler all decide it, so an efficient machine is a clean one.
- Measure it as the time to fill a known receiver volume — which is also how a slow-filling compressor is diagnosed.
Surveyor follow-up: compressor taking twice as long to fill with the discharge pressure correct — clearance, valves or cooling first?
Full theory: Air Compressor Working — Cycle, Volumetric Efficiency, Coolers & Capacity -
12 Air compressor running and takes more time to fill, reasons?
Also asked: “Air compressor taking long time to fill the bottle. What all are the reasons for this?”
Answer
A slow-filling compressor is leaking, losing clearance or starved of cooling — time the fill and work the list in that order.
- A leaking suction or delivery valve wastes the work, and worn rings and excessive clearance cut the volume delivered.
- Fouled after-cooler or intercooler raises the delivery temperature, so less air enters the receiver per stroke.
- A blocked inlet filter, a failing unloader or a leaking suction line from the receiver cuts the working capacity.
- Time a fill from empty at a set pressure and log it — a rising fill time is the first sign of clearance or valve wear.
Surveyor follow-up: fill time doubled with the valves renewed and the cooler clean — is the unloader, the filter or the rings?
Full theory: Air Compressor Working — Cycle, Volumetric Efficiency, Coolers & Capacity -
13 Bilge high level in your watch,actions
Answer
A rising bilge is a leak until proven otherwise: start the pumps, find the ingress and log the time and position.
- Note the position and time, then start the bilge pumps with the shore connection open and the overboard valves lined up.
- Send a second hand to locate the ingress — a burst pipe, a cracked sea chest or a hull opening above the waterline.
- At sea use direct bilge suction and the bilge injection valve if the flooding is serious; in port pump to the bilge tank or ashore.
- Log levels and actions each watch, and never silence the alarm without a proven cause — a checked bilge is not a fixed bilge.
Surveyor follow-up: bilge level rising slowly for three hours with both pumps running — find the leak, sound the hull, or keep pumping?
Full theory: The Bilge System the Separator Serves -
14 In air compressor , what is the difference between suction and exhaust valve
Answer
Both are one-way spring-loaded valves; the difference is the pressure behind them and the job each does in the stroke.
- The suction valve lets air into the cylinder and prevents back flow out; the delivery valve does the reverse.
- On the suction stroke the cylinder pressure falls until the air behind the suction valve overcomes its spring and opens it.
- On the delivery stroke the delivery valve opens to the receiver and closes to stop back flow when pressure equalises.
- They differ in design because the piston velocity, cycle time and gas pressure differ between the two events.
Surveyor follow-up: compressor reaching pressure but slow to fill with both valve sets renewed — is it the springs or the lift?
Full theory: Air Compressor Construction — Pistons, Rings, Valves & Running Gear -
15 List out at least five running air compressor system with indications, causes and remedial actions. B) what are the purpose of solenoid valve in the AC system ?
Answer
Five running faults account for most air compressor trouble: no air, not enough air, high temperature, high current and low receiver pressure.
- No air delivered: intake blocked, suction filter plugged, unloader stuck, valve damaged, leaks in piping, or a blown gasket.
- Not enough air: demand above the rating, partial intake blockage, dirty suction filter, or a stuck unloader cutting the delivery.
- Too hot: cooling water fouled or low, poor intercooling, or valves leaking and reheating the air each stroke.
- High current: high pressure, high temperature, or a seized machine — shut down rather than let the motor carry it.
- Low receiver pressure: leaks, an unloader stuck open, a suction fault, or the safety valve passing to atmosphere.
Surveyor follow-up: receiver pressure low with the safety valve proved tight and the filters clean — where is the air going?
Full theory: Air Compressor Maintenance — Lapping, Clearances & Overhaul -
16 State what symptoms would indicate leakage across vane seals. (8) LY (b) State what steering gear tests you would carry out before a voyage begins. (8) i> . . [ 8 ) To achieve the optimum performance from a main air comp
Also asked: “State what symptoms would indicate leakage across vane seals. (8) LY (b) State what steering gear tests you would carry out before a voyage begins. (8) i> . . [ 8 ) To achieve the optimum performance from a main air compressor, describe the routine / maintenance necessary on the following components; S (a) Unloade- (4) (b) Air intak> filter (4) (c) Suction/ Discharge valves (4) (d) Intercoolers (4”
Answer
Two questions in one: vane-seal leakage shows as lost efficiency and heat, and the pre-voyage steering tests are a fixed list.
- Vane-seal leakage drops free air delivery at the same speed and load, because the compressed air leaks back across the vane tips.
- The compression work is redone each stroke, so discharge temperature rises and the machine runs hotter than the maker’s curve.
- Oil carried across the vane tips reaches the air system — check the receiver, the aftercooler and the drain for oil.
- The pre-voyage steering test is not less than 12 hours before departure, or weekly on short voyages, covering the main gear, the auxiliary, the remote control and the bridge position.
- It also covers the emergency power supply, the rudder indicator, and the power failure alarms for both the remote control and the steering gear power unit, with a full visual inspection while running.
Surveyor follow-up: vane-seal leak suspected on a ship whose last steering test was 16 hours before sailing — which part of that test was late?
Full theory: Steering Gear Checks and Tests — Daily Rounds, the 12-Hour Test and Drills -
17 Type of pump for hypermist system (fresh water or sea water
Answer
Hypermist runs on fresh water with a high-pressure plunger pump — around 200 litres per minute at some 70 bar — to atomise it.
- A plunger-type reciprocating pump supplies the high pressure, with zoned solenoid valves opening the branch to the fire zone.
- Fresh water is the medium, so the circuit is a closed freshwater tank, pump and nozzle ring rather than a seawater system.
- Nozzles pass roughly 12–20 litres per minute at about 50 bar, breaking the stream into a fine cooling fog.
- Testing uses clean water on a schedule, because a blocked nozzle is a zone that will not fight a fire.
Surveyor follow-up: hypermist pump tripped on high pressure with nozzles proved clear — is the unloader, the bypass or the relief?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
18 What is difference bet direct bilge suction eme bilge suction
Answer
Direct bilge suction comes straight from the sea with no mud box; the emergency suction joins the cooling seawater line.
- Direct bilge suctions are fitted on each side of the machinery space and in the tunnel, with mud boxes at platform level.
- Emergency bilge suction is led into the main cooling seawater pump suction line, and mud or strum boxes are to be avoided.
- The direct suction is the independent one — it works when the cooling line is the thing that has failed.
- Each suction has its own screw-down non-return valve, and the pumps must be self-priming or quickly primed.
Surveyor follow-up: ER flooded with the cooling suction line damaged — which suction do you open, and what protects the pump?
Full theory: The Bilge System the Separator Serves -
19 What is requirement for pumping er bilges
Answer
Engine-room bilges need two independent pumps, direct suctions each side, and a system that cannot be lost with the cooling line.
- The bilge system is entirely separate from other systems, and the main bilge is connected to two bilge pumps.
- Direct bilge suctions are fitted on each side of the machinery space and in the tunnel, with accessible mud boxes at platform level.
- The emergency bilge suction is led into the main cooling seawater pump suction line, with mud or strum boxes to be avoided.
- Each suction has a screw-down non-return valve, and the pumps must be self-priming or quickly primed for the emergency.
Surveyor follow-up: engine room flooded with the cooling suction line ruptured — which suction opens, and what keeps the pump safe?
Full theory: The Bilge System the Separator Serves -
20 What is the process in Air compressor?
Answer
A reciprocating compressor draws, compresses and delivers: intake through the suction valve, compression in the bore, discharge to the receiver.
- The suction stroke opens the suction valve and fills the cylinder while the delivery valve stays shut.
- On the compression stroke both valves close until the cylinder pressure exceeds the spring load on the delivery valve.
- The delivery valve then opens and the air is forced out to the after-cooler and the receiver at the higher pressure.
- The clearance volume keeps a cushion of air, and each cycle gives one charge — the basis of capacity and of the compression ratio.
Surveyor follow-up: compressor delivering at low pressure with the receiver at normal — is it the valves, the unloader or the gauge?
Full theory: Air Compressor Working — Cycle, Volumetric Efficiency, Coolers & Capacity -
21 Why use after cooler in Main Air Compressor?
Answer
The after-cooler takes the heat out of the delivered air so the receiver and the starting air stay at a workable temperature.
- It reduces air temperature and volume while raising density, which improves the volumetric efficiency of the whole set.
- Cold delivered air keeps the suction and delivery valves cleaner, without carbonised oil fouling them.
- It lowers the risk of an explosion in the cylinder, helps lubrication, and makes moisture separation easier at the drains.
- Without it the receiver runs hot, the air holds more moisture, and every downstream consumer pays for it.
Surveyor follow-up: after-cooler bypassed with the receiver at normal and delivery temperature high — is the water or the bypass first?
Full theory: Air Compressor Working — Cycle, Volumetric Efficiency, Coolers & Capacity -
22 With reference to air compressors state why: 1 (a) Piston ring freeness and condition is important. (4) (b) Correct clearance volume is critical to performance (4) (c) Suction and delivery valves need to be maintained in
Also asked: “With reference to air compressors state why: 1 (a) Piston ring freeness and condition is important. (4) (b) Correct clearance volume is critical to performance (4) (c) Suction and delivery valves need to be maintained in good working condition. (4) (d) Suction filters should be of large size and kept clean. (4”
Answer
Rings, clearance and valves are the three things that decide a compressor’s volumetric efficiency — take one away and the air stops.
- Rings must be free and in good condition: a stuck or worn ring lets high-pressure air back past the piston on every stroke.
- Clearance volume is critical: too little and the machine cannot fill, too much and the space reheats and wastes power on compression.
- Suction and delivery valves must lift correctly — improper lift cuts volumetric efficiency, and the lift is checked from the running parameters.
- So performance is proved on the machine, not on the bench: free air delivery, discharge temperature and suction pressure read together.
Surveyor follow-up: FAD down with rings and valves proven — is the clearance volume, the intake or the demand the cause?
Full theory: Air Compressor Maintenance — Lapping, Clearances & Overhaul -
23 With reference to multi-stage, single crank air compressors explain why: , (a) (i) Bumping' clearances are checked. (3) (ii) Bottom end adjustment does not affect ‘bumping' clearance. (3) (iii) The clearance is not adjus
Also asked: “With reference to multi-stage, single crank air compressors explain why: , (a) (i) Bumping’ clearances are checked. (3) (ii) Bottom end adjustment does not affect ‘bumping’ clearance. (3) (iii) The clearance is not adjusted on one stage alone. (3) (b) Describe how bumping clearances are corrected. (7”
Answer
Bumping clearance is what the piston must re-compress before the suction valve opens; check it because it eats the suction stroke.
- At the end of the compression stroke the clearance space is full of high-pressure air that must expand before the cylinder is low enough.
- The expansion eats a large part of the suction stroke, so a large bumping clearance directly reduces volumetric efficiency.
- It is checked because it grows in service with wear in the crankpin bearing, the connecting rod and the cylinder liner.
- Bottom-end adjustment changes the rod length and does not alter it, and the clearance is not adjustable at all — it is a condition to measure.
Surveyor follow-up: FAD low with rings and valves proven and the bottom end new — is the bumping clearance or the clearance volume?
Full theory: Air Compressor Maintenance — Lapping, Clearances & Overhaul -
24 air compressor unloader working
Also asked: “air conditioner unloader working”
Answer
The unloader is the capacity control: it lifts the delivery valves or holds them open so a single-stage set stops short of full pressure.
- Set around 24 bar, it lets a single-stage compressor reach working pressure without a two-stage set.
- Lift-type or spring-loaded unloader opens the delivery valves and the compressor idles, unloading the whole machine.
- With the outside temperature falling, suction pressure stays steady so capacity control is not chasing load.
- An unloader that does not lift means the compressor runs against rising pressure until the safety valve lifts — that is the fault to find.
Surveyor follow-up: compressor tripping on high discharge with the unloader proved free — is the setting, the control or the sensor?
Full theory: Air Compressor Working — Cycle, Volumetric Efficiency, Coolers & Capacity
Source: 123 written papers and surveyor oral banks, 24,613 entries, merged into 17,210 topics. Ticks are stored on this device only.