Piping & Hydraulics — Most Asked Questions
57 questions asked about piping & hydraulics across the General and Fn 3 and Fn 4b and Fn 6 papers, heaviest first.
Learn the system first
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1 Why not pv breaker instead of pv valve?
Answer
The PV valve is the working breather; the PV breaker is the liquid-seal backup that only acts when pressure or vacuum goes abnormal.
- The PV valve handles normal tank breathing on loading, discharge and temperature change.
- The PV breaker is a U-tube manometer filled with glycol solution that blows liquid to deck on over-pressure or sucks it toward tanks on vacuum.
- Set above the valve — about +1800 mm water pressure side and −700 mm vacuum side — so it never works in normal service.
- Fitted on the IG main to save the tanks if every gas outlet is shut during loading or a valve slams: last defence, not daily regulation.
Surveyor follow-up: glycol level in the breaker keeps dropping with no alarm — what is it telling you?
Full theory: Deck Foam & Inert Gas (IG) Systems on Tankers -
2 If second stage relief valve lifting Reasons?
Also asked: “compress 2nd stage relief valve got lifted , reason ?”
Answer
A lifting second-stage relief means interstage pressure is high — the fault sits in the second stage, not the first.
- High intercooler pressure points forward: suction or discharge valves of the succeeding (second) stage passing or broken.
- Prove it loaded versus unloaded: pressure high loaded and steady unloaded marks the preceding stage’s suction valves; pressure falling toward zero marks its discharge valves.
- If interstage pressure climbs until the safety valve blows, stop and open up the second stage — running on invites a burst cooler.
- Check also for choked intercooler passages and a wrongly set or dribbling relief valve before condemning the stage.
Surveyor follow-up: interstage pressure low instead of high — which stage do you open first?
Full theory: Air Compressor Safety — Relief Devices, Receivers & SOLAS -
3 What is back pressure valve?
Also asked: “Function of back pressure valve in refer”, “what is the need for back pressure valve if we have solenoid valve”
Answer
The back-pressure valve holds evaporator pressure up: it stops the evaporator freezing, lets two rooms share one compressor, and answers a pilot solenoid.
- Spring-loaded against evaporator pressure, it throttles flow to keep the coil at its set pressure and temperature.
- Uses: protect liquid chillers from freezing, stop frost on near-freezing air coolers, run two evaporators at different temperatures on one compressor.
- In the refer plant it sits where flow is lightest — often the vegetable room — as a spring non-return holding its branch pressure.
- It also doubles as a solenoid valve under pilot control for load-based modulation.
Surveyor follow-up: veg room too cold with fish room normal — back-pressure valve, thermostat or solenoid, and which way do you turn it?
Full theory: Steam Traps, Pressure Reducing Valves (PRVs) & Condensate Drainage -
4 Globe valve overhaul
Also asked: “globe valve overhauling and checks”
Answer
Overhaul globe valves seat-first: clean the lands, lap the disc, renew the gland, prove full travel.
- Back off the jam screw, lift the cover, discard seat and cover gaskets, clean every land with soft tools — never wire brushes on seats.
- Inspect seats for wire-drawing and burrs, damping plates for cracks, guards for damage.
- Lap disc to seat, renew packing and gaskets, set the gland to seal without seizing the spindle.
- Prove by full open-to-shut travel with no weep at rated pressure before boxing up.
Surveyor follow-up: valve passes shut but weeps at the gland under pressure — packing, seat or spindle, and what do you tighten?
Full theory: Globe, Gate & Non-Return (SDNR) Valves: Working, Troubleshooting & Overhaul -
5 Shore coupling dimensions
Answer
The international shore coupling is one standard flange: 178 mm outside, 64 mm bore, 132 mm bolt circle, four 16 mm bolts.
- Outside diameter 178 mm, inside 64 mm, bolt circle 132 mm with four 19 mm slots to the flange edge.
- Flange 14.5 mm minimum in steel for 1 newton per square millimetre service with flat face one side.
- Four 16 mm bolts 50 mm long with nuts and washers, kept with the coupling and hose adapter.
- Stowed ready for the shore main in any port — the flange that lets a strange fire main feed your hydrants.
Surveyor follow-up: shore main connected but leaking at the flange — gasket, bolts or faces, and what do you check first?
Full theory: Globe, Gate & Non-Return (SDNR) Valves: Working, Troubleshooting & Overhaul -
6 how hydraulic jack works
Also asked: “hydraulic jack working”, “How to use hydraulic jack”
Answer
A hydraulic jack trades strokes for force: small pump piston feeds a big ram piston through check valves — pressure times area does the lifting.
- Pump strokes push oil past the inlet check into the ram chamber; the outlet check holds it there.
- Ram area many times the pump area multiplies force by the same ratio at the cost of travel.
- Dial gauge on the lifted shaft with pressure noted both ways proves load against lift for crankshaft work.
- Release valve meters oil back to suction for a controlled lower — never crack it under full load hands-on.
Surveyor follow-up: jack lifts but creeps down under load — inlet check, outlet check or seals, and what proves it?
Full theory: Marine Central Cooling Water System (HT / LT / SW) -
7 Fiva valve working
Also asked: “Feva valve working”
Answer
FIVA valves meter fuel and exhaust hydraulics on electronic engines: proportional oil pressure moves the actuator to VIT and timing orders.
- Proportional solenoids turn controller current into hydraulic pressure on the fuel and exhaust actuators.
- On fuel pumps that pressure shifts injection timing and quantity like a VIT barrel under electronic command.
- On exhaust valves it times opening and closing against crank angle instead of a cam.
- Failure signs are timing spread and slow response — check control oil, solenoids and feedback before the pump itself.
Surveyor follow-up: timing spread on an ME-C engine with control oil normal — FIVA, feedback or controller, and what proves it?
Full theory: The Valve Gear and Fuel Injection — Valves, Camshaft Drive, Pumps and Injectors -
8 How will you find out air starting valve is leaking?
Also asked: “ME starting air valve leaking, how you come to know?”, “Air start valve leaking how to check”, “How will you know leaking starting air vale”
Answer
A leaking start valve heats its own branch: hot manifold pipe, changed thermal patch, exhaust smell and drain blow tell the story.
- Feel each branch pipe from the manifold — the leaking unit runs hot from combustion gas blowing back.
- Thermal patches change colour and bursting discs threaten as back-pressure builds in the manifold.
- Crack the indicator cock and give an air kick: starting air blowing out proves that unit’s valve leaks.
- Shut fuel to the leaking unit and change the valve at the first chance — running on invites a manifold explosion.
Surveyor follow-up: two branches warm with one clearly hot — leak, normal firing order or distributor fault, and what proves it?
Full theory: Starting Air System Physics, Explosions & Air Distributor -
9 After cleaning the cooler are hydraulically pressure tested normally 1.5 times the working pressure
Also asked: “• After cleaning the cooler are hydraulically pressure tested normally 1.5 times the working pressure”
Answer
Cleaned coolers prove at one-and-a-half times working pressure: boilers hold thirty minutes with hammer-tested welds.
- Apply test pressure gradually through feed lines and hold — thirty minutes on boilers with leak watch throughout.
- Hammer-tap weld repairs under pressure to prove soundness without hiding weeps.
- Charge-air and oil coolers follow the same discipline after chemical and brush cleaning.
- Retube past 10% failed tubes; log plugged tubes against the maker limit before boxing up.
Surveyor follow-up: pressure holds but one weld weeps under the hammer — accept, caulk or re-weld?
Full theory: Cooling, Lubrication and Fuel — Systems and the Tanks Checked Before Starting -
10 Corrosion can be protected by means of preservative coating (Anti corrosive paints) inside the shell and water boxes and by means of anodes such as zinc fitting inside water boxes
Also asked: “• Corrosion can be protected by means of preservative coating (Anti corrosive paints) inside the shell and water boxes and by means of anodes such as zinc fitting inside water boxes”
Answer
Cooler corrosion is beaten inside and out: coatings isolate steel, zinc anodes sacrifice themselves, flow direction saves entrances.
- Anti-corrosive paint lines shells and water boxes against seawater attack.
- Zinc anodes inside water boxes waste first, sparing tubes, plates and covers.
- Reverse flow periodically so impingement-prone tube entrances become outlets in turn.
- Cast-iron covers graphitise unprotected; fabricated steel needs galvanizing inside and out after weld dressing.
Surveyor follow-up: anodes wasted to stubs with coating intact — renew now or run to the next overhaul?
Full theory: Cooling, Lubrication and Fuel — Systems and the Tanks Checked Before Starting -
11 Close suction and discharge valve
Also asked: “Close cylinder valve”, “CLOSE THE DRAIN VALVE”
Answer
Isolate pumps suction-first, discharge-second: shut in, vent, lock, tag and prove dead before hands go in.
- Close suction then discharge with the set stopped — never throttle a running centrifugal to shutoff head.
- Cylinder and drain valves follow the same order with pressure vented to zero on gauges.
- Lock and tag both valves with the permit in the key safe until work completes.
- Running near shutoff wastes power as heat and vibration, bending shafts and cooking seals.
Surveyor follow-up: discharge slammed shut on a running pump — throttle, trip or water hammer, and what breaks first?
Full theory: Globe, Gate & Non-Return (SDNR) Valves: Working, Troubleshooting & Overhaul -
12 How to remove exhaust valve guide
Also asked: “how to remove exhaust valv guide bush ( how valv spindle fitted to the valv”, “How will you take out exhaust valve guide?”
Answer
Pull guides with push-bolts and jacks, never hammers: even pressure on the bush with the spindle path protected.
- Strip spring seat, spring and retainer, then screw push-bolts evenly to draw the guide without cocking.
- Jack assemblies with handle bars move casings, covers and bearings together — tap only through copper or wood with a second pair of hands.
- Protect threads, seals, keys and knock pins on every draw; bush and spindle fit proved on reassembly.
- Log bush wear against maker limits before refitting the spindle to its guide.
Surveyor follow-up: guide seized solid with push-bolts loaded — heat, press or cut, and what do you protect?
Full theory: Exhaust Valve Actuation, Air Spring Mechanics & Spindle Metallurgy -
13 back pressure valve in veg room ?
Answer
The veg-room back-pressure valve holds its coil warmer than the fish room on the same suction line.
- Spring-loaded against evaporator pressure, it throttles flow to hold near 4–5 degrees in the vegetable room.
- Without it refrigerant floods the warmest coil and starves the coldest — fish at minus 18 suffers first.
- Outlet legs join one common return, so pressure, not thermostats alone, shares the flow.
- Prove by coil temperatures and superheat per room with the valve set to the book pressure.
Surveyor follow-up: veg room freezing with fish room warm — valve stuck open or shut, and which way do you turn it?
Full theory: The Refrigeration Compressor -
14 As for abrasion of fitting part with bearings, if the inner race of
Answer
A spinning inner race frets its seat: creep, brinelling and washboard finishes mark wrong fits and dirty assembly.
- Creep from loose fits lets the race walk the shaft, polishing fretting flats into both faces.
- Vibration brinells balls into corduroy raceways that rumble long before they seize.
- Dirt, sand and mishandled storage seed abrasion that grows into spalling and breakaway.
- Strip every failed bearing to read races and rollers — the pattern names fit, dirt or shock.
Surveyor follow-up: polished fretting on the shaft with the bearing intact — fit, dirt or vibration, and what size do you measure?
Full theory: Engine Bearings — Renewal, Crosshead to Thrust Block -
15 Back pressure valve in ref. System
Also asked: “back pressure valve in reefer system”, “why we have back pressure valve in ref system”
Answer
The back-pressure valve holds its coil warmer than colder rooms on one suction line.
- Spring-loaded against evaporator pressure to hold the set coil temperature by pressure.
- Veg room near 4–5 degrees against fish rooms near minus 18 on the same compressor.
- Without it refrigerant floods the warm coil and starves the cold — pressure, not hope, shares the flow.
- Prove by coil temperatures and superheat per room with the setting at book pressure.
Surveyor follow-up: veg room freezing with fish room warm — stuck open or shut, and which way first?
Full theory: The Refrigeration Compressor -
16 Crankcase relief valve ‘
Also asked: “CC relief valve”
Answer
Crankcase reliefs vent explosions fast: one per door past 30 cm bore, 45 square centimetres each with 115 per cubic metre of volume.
- Spring setting opens at 0.07 bar internal and snaps shut positively once relieved.
- Test stopped with the flame trap off: lift the disc by hand for smart open and rapid close, oiled and free.
- Flame traps on every valve stop the vented flame lighting the engine room.
- Cool thirty minutes before opening doors after any alarm — the mist is the warning, not the fire.
Surveyor follow-up: disc lifts lazy with the trap clean — spring, hinge or oil, and do you adjust or renew?
Full theory: Scavenge Fires, Trunk Safety & Relief Devices -
17 Fitting exhaust valves with valve rotators
Also asked: “• Fitting exhaust valves with valve rotators”
Answer
Rotators spin exhaust valves a little each lift: even heat, polished seats and no hammered pits from trapped grit.
- Winged stems catch exhaust flow to rotate; Rotocap mechanisms turn smaller valves the same way.
- Rotation spreads heat evenly round sealing faces instead of guttering one side.
- Polishing action wipes deposits between valve and seat each cycle against vanadium and sodium ash.
- Stellite-coated seats stretch overhaul intervals further with rotators fitted.
Surveyor follow-up: one valve guttered with the rotator fitted — seized rotator, fuel or cooling, and what proves it?
Full theory: Exhaust Valve Actuation, Air Spring Mechanics & Spindle Metallurgy -
18 How exhaust valve works
Also asked: “How does exhaust valve actuation and closing”
Answer
Exhaust valves open on 120-bar hydraulics and slam shut on air plus cylinder pressure with a throttle valve cushioning the seat.
- Hydraulic actuator lifts against spring air to open on electronic or cam timing.
- Rising piston pressure plus spring air drives closure; the throttle valve meters oil escape to soften seating.
- Without the throttle the valve hammers its seat as line pressure collapses at opening.
- Separate camshaft lube pumps get primed before starting or the first lift runs dry.
Surveyor follow-up: valve hammers shut with hydraulics normal — throttle, air or timing, and what do you adjust?
Full theory: Exhaust Valve Actuation, Air Spring Mechanics & Spindle Metallurgy -
19 How you will remove valve seat
Also asked: “How will you replace valve seat”
Answer
Pull seats with yokes, push-bolts and pullers: jam screw off, cover up, yoke off, seat out on clean faces.
- Back the jam screw four turns, lift cover nuts and cover, free the yoke set screws and lift the yoke.
- Discard cover and seat gaskets; clean every landing bright with soft tools — never wire brushes on seats.
- Read seats for burrs, wire-drawing and breakage before lapping or renewal.
- Rebuild with new gaskets, prove full travel and pressure-tightness before boxing up.
Surveyor follow-up: seat weeps after lapping with the yoke correct — lap again, renew or check the guard?
Full theory: Globe, Gate & Non-Return (SDNR) Valves: Working, Troubleshooting & Overhaul -
20 Int shore coupling use and dimensions
Also asked: “International shore coupling-dimensions and purpose”
Answer
The shore coupling lands foreign water aboard: standard 178 mm flange with 64 mm bore on a 132 mm bolt circle.
- Steel flange for 1 newton per square millimetre service with flat face and ship-side coupling.
- Four 19 mm slots to the flange edge on the bolt circle with 14.5 mm minimum thickness.
- Four 16 mm bolts with nuts, washers and gaskets kept with the connection at the gangway.
- Use is any port’s main feeding any ship’s hydrants — one flange ends adapter hunts in a fire.
Surveyor follow-up: shore main connected but weeping at the flange — gasket, bolts or faces first?
Full theory: Globe, Gate & Non-Return (SDNR) Valves: Working, Troubleshooting & Overhaul -
21 What is caba compressed air breathing apparatus
Answer
CABA is SCBA under another name: cylinder air through a demand valve to a sealed mask for rescue and fire work.
- Cylinder near 210 bar through a reducing valve near 5.5 bar to a breathing-rate demand valve.
- Positive-pressure mask holds excess inside over outside air so leaks flow outward, not inward.
- About 1800 litres giving near 36 working minutes with roughly 9 minutes past the whistle.
- Donning checks prove pressure, leak-down, demand flow and 50–60 bar alarm before entry with lifeline and bypass ready.
Surveyor follow-up: demand valve free-flowing on donning — adjust, isolate or swap sets, and do you enter?
Full theory: LSA Chapter 1: Categories of LSA & Personal Life-Saving Appliances -
22 How would you change a gasket in the flange of a SW pipe if the gasket has worn out
Answer
Renew sea-water gaskets isolated and drained: shut both sides, vent, crack flanges even, clean, renew and box up torqued.
- Isolate suction and discharge with blanks or double valves proved shut and the line drained to bilge.
- Slacken flange bolts evenly, part faces without levering on sealing lands, and lift the worn gasket whole.
- Wire-brush and inspect flange faces for pitting; cut or fit the new gasket to bore, pitch and holes.
- Lubricate threads, tighten in star sequence to torque, then pressure-prove with the sea chest watched.
Surveyor follow-up: flange weeping after renewal with bolts hard home — faces, gasket seating or uneven pull-up first?
Full theory: Ship Pipelines — Seawater, Bilge, Ballast & Fuel Systems -
23 Over hauling of air starting valve?
Answer
Overhaul starting-air valves by exchange: fit the tested spare, then strip, lap and bench-test the removed unit.
- Replace regularly with an overhauled spare so no cylinder ever waits on a bench job.
- Strip spring, pistons and rings with parts laid in order; inspect bursting cartridges or discs for corrosion.
- Grind the valve into its seat with fine lapping paste, checking wings clear everywhere after grinding.
- Rebuild and bench-test tight with compressed air before the spare returns to the rack.
Surveyor follow-up: sluggish start with a freshly overhauled valve and full bottles — seat, safety cartridge or timing first?
Full theory: Starting the Engine — Air Start Valve, Distributor and the Four Interlocks -
24 CLOSE STEAM VALVE
Also asked: “Close necessary valves”
Answer
Close steam valves in order: throttle down, drain condensate ahead, shut slowly against water hammer, prove shut.
- Ease load off the line before touching the valve — slamming a live main hammers traps and joints.
- Drain condensate through traps and drain cocks so no pocket sits to flash or slug the seat.
- Shut steadily to the back seat where fitted, proving zero passage with downstream pressure falling.
- Tag and log the closure with the system it isolates — an unlogged shut steam valve ambushes the next watch.
Surveyor follow-up: hammering after a fast steam-valve closure with drains shut — drainage, speed or trap first to blame?
Full theory: Steam and Condensate System — Interactive One-Line Diagram -
25 Close main air stop valve and lack staring system
Answer
Immobilise the engine by shutting the main starting-air stop and locking the starting system against any crank.
- Shut the main air stop valve to the distributor and vent trapped air downstream.
- Engage turning gear or its interlock so a bridge order cannot admit air to the cylinders.
- Lock levers, tag valves and prove the block by attempting control movement with no response.
- Log the immobilisation with time and authority — locked starting air is the permit’s first line.
Surveyor follow-up: bridge rings with the stop shut but the gear disengaged — what still blocks the start?
Full theory: Starting the Engine — Air Start Valve, Distributor and the Four Interlocks -
26 Accumulator in hydraulic line
Answer
Accumulators store pressure energy: nitrogen over oil, they absorb shocks, hold pressure and smooth the pump’s pulses.
- A bladder or piston separates nitrogen precharge from hydraulic oil, storing energy when pressure rises.
- They absorb water-hammer shocks from sudden valve closure and high oil temperature, low pressure or vibration.
- They smooth pump pulsations and hold system pressure for actuators during pressure drops or power loss.
- The precharge gas and the relief device set their limits — wrong precharge and the accumulator becomes a hazard, not a helper.
Surveyor follow-up: accumulator blowing its relief repeatedly with precharge proved low — recharge, check the relief or find the shock source?
Full theory: Hydraulic Drives for Deck Machinery — Fluid, Pumps and Circuits -
27 And then I will take the old gasket and draw it over a new gasket material . And prepare the flange by cleaning it properly and then fit the new gasket
Answer
Renovation is sound practice: draw the old gasket on new material, clean the flange properly, then fit and tighten evenly.
- The old gasket is the template — draw it on the new sheet so the bore, the bolt holes and the seating match exactly.
- Clean both flange faces thoroughly, checking for scoring, pitting or a flat that will not seal.
- Fit the new gasket dry or lightly dressed, and tighten the bolts in star sequence to the specified torque.
- Then pressure-test and warm the line through; a joint that is not proved is a joint that will weep in service.
Surveyor follow-up: flange re-gasketed with a new sheet drawn off the old, but bolts at full torque after one pull — what was missed?
Full theory: Ship Pipelines — Seawater, Bilge, Ballast & Fuel Systems -
28 At night any difference in pv valve operation - i said no difference
Answer
No, the P/V valve does not care about night: it is a mechanical set point on tank pressure, and the only night factor is the tank’s state.
- A P/V valve is a spring-loaded relief and vacuum valve, so its setting is fixed and unaffected by light or time of day.
- What changes is the tank: temperature drop at night raises vacuum, and filling or heating during the day raises pressure.
- In hot weather the tank breathes out at night as the gas cools and contracts; in cold conditions it draws air in.
- So the answer is that there is no operating difference — the same valve handles both, and the breathing rate changes instead.
Surveyor follow-up: tank venting heavily only at night with the setting proved — is the valve, the breather or the tank condition?
Full theory: Ship Pipelines — Seawater, Bilge, Ballast & Fuel Systems -
29 Bilge injection valve Solas regulations
Answer
Bilge injection is the emergency valve that lets the sea into the engine-room bilges to save the ship: it must work in seconds.
- Keep it ready, identifiable and operable from the steering gear flat and the engine control position.
- Regulations require emergency escape breathing devices in machinery spaces, with the bilge and injection arrangements on the fire control plan.
- Valve and sea chest line up for immediate opening, with the discharge led to a safe space on purpose — not randomly.
- Prove it on the schedule and log the test: an emergency valve proved once at drydock is an untested valve.
Surveyor follow-up: injection valve seized shut with a flooding engine room and no duplicate — force it, open the sea chest or use portable pumps?
Full theory: The Bilge System the Separator Serves -
30 Bilge injection valve testing
Answer
Test the bilge injection on schedule with the ship’s position and time logged — an emergency valve proved once is unproved.
- Open the injection slowly on order, watching the bilge level fall with pump suction proved and strainers clear.
- After the test shut, drain and re-lash the valve and pump the bilges back to normal working level.
- Check the overboard and sea chest line-up again, and confirm the valve is handwheel-free and correctly sealed.
- Record date, time, level change and valve condition — the log is the proof, not the act of opening it.
Surveyor follow-up: injection valve tested with the overboard shut so water went nowhere — re-test or accept the record?
Full theory: The Bilge System the Separator Serves -
31 Check pump and by pass valve
Answer
Pumps sit idle on bypass, then shift to duty: the spring-loaded bypass holds them relieved until discharge pressure lifts it.
- When a pump is not in use it is prevented from motoring and relieved of a starting load by a spring-loaded discharge valve.
- The valve stays in bypass until the pump starts and its discharge pressure is sufficient to move it.
- Valve movement then automatically closes the bypass and opens the isolating connection to the system.
- A pump that will not come onto line is usually a bypass that will not shift — check it before condemning the pump.
Surveyor follow-up: pump runs but stays on bypass with relief discharging hot — valve, relief setting or pump discharge first?
Full theory: Hydraulic Drives for Deck Machinery — Fluid, Pumps and Circuits -
32 Diff between pv valve and pv breather
Answer
Same job, different stage: the breather is the first line, the P/V valve takes over when the vent cannot keep up.
- A P/V breather vents gently all the time on the smallest pressure or vacuum the tank can tolerate.
- A P/V valve takes higher loads, with settings chosen so the tank top is never overstressed or collapsed.
- Even 0.24 bar acting on a large tank area gives a huge total load — distension or inward collapse follows without them.
- State both settings, not just the device: the damage case is what the surveyor is testing your answer against.
Surveyor follow-up: breather blocked on a laden tank with the P/V valve doing all the venting — clear, reset or load down?
Full theory: Ship Pipelines — Seawater, Bilge, Ballast & Fuel Systems -
33 How to repair cracked bonnet of a valve made up of cast iron?
Also asked: “• How to repair cracked bonnet of a valve made up of cast iron?”
Answer
A cracked cast-iron bonnet is not a welding job: the casting is condemned and the bonnet renewed, because heat on cast iron invites fracture.
- Cast iron cracks and cannot be safely welded — the repair is a new bonnet or a new valve, never a patch.
- Isolate, drain and depressurise the line, then strip the valve and confirm the crack sits only in the bonnet.
- Fit the replacement bonnet with new gaskets, renewed trim and the stem gland repacked to maker figures.
- Pressure-test the valve, then re-test on the system and log the renewal — a welded bonnet returns the same crack.
Surveyor follow-up: bonnet crack welded in port with the gate seized — accept, machine a new seat, or renew the valve?
Full theory: Globe, Gate & Non-Return (SDNR) Valves: Working, Troubleshooting & Overhaul -
34 How will u replace the gasket in the flange of the steam line?
Answer
Steam-line gaskets are renewed cold and slowly: isolate, drain the line completely, ease the flange even, and refit torqued.
- Shut and lock the isolation valves, vent the line to atmosphere and prove it cold and empty before breaking any joint.
- Draw old gasket material on a new sheet to the exact size — the seat ring imprint is the pattern, not guesswork.
- Clean and inspect both flange faces for scoring, pitting or warping before the new gasket goes anywhere near them.
- Fit the gasket dry or lightly dressed, tighten the bolts in star sequence to the specified torque, then pressure-test and warm through.
Surveyor follow-up: flange weeping with bolts at torque and a new gasket fitted — faces, gasket seating or uneven pull-up first?
Full theory: Steam and Condensate System — Interactive One-Line Diagram -
35 In case there are partial flaws on fitting part with bowl, they shall be repaired and smoothed with a set of files and sand paper. If the flaws are formed in a continuous ring shape, it shall be replaced
Answer
Valve-seat fitting work is graded: local flaws are dressed smooth, a continuous ring of damage means the part is replaced.
- Partial flaws on the bowl are repaired and smoothed with files and sandpaper, restoring the sealing land.
- A flaw running as a continuous ring round the bowl cannot be dressed out — the fitting or seat is renewed.
- Dress to the existing profile rather than cutting a new step, or the valve will not seat when reground.
- After dressing, prove with the matching lapping compound and check the face width, then pressure-test the valve.
Surveyor follow-up: ring-form flaw dressed repeatedly on the same seat — keep dressing or renew the fitting, and why?
Full theory: Globe, Gate & Non-Return (SDNR) Valves: Working, Troubleshooting & Overhaul -
36 Isolating valve and when used
Answer
Isolating valves stop a line, not the flow: they shut a system off for repair, cleaning or draining and hold it shut.
- Globe, gate and stop valves give positive shut-off for work on a line, with a handwheel and a gland you can repack.
- Used before any dismantling, behind a strainer or cooler when it is changed, and for isolating a leaking branch.
- Anniversary-type and quarter-turn valves differ in use, but the duty is the same — positive isolation, not throttling.
- Tag, lock and log the isolation; a valve left unlocked after a job is the classic cause of a reflooded system.
Surveyor follow-up: branch isolated for a strainer change and found unlocked the next watch — how does that get closed out?
Full theory: Globe, Gate & Non-Return (SDNR) Valves: Working, Troubleshooting & Overhaul -
37 LEAKY SOLENOID VALVE
Answer
A leaking solenoid passes refrigerant when the compressor is off — the coil is fine and the valve is not.
- Foreign matter between valve and seat, a broken or weakened spring, or a worn valve and seat cause the leak.
- Symptom is the box running cold and the space not holding temperature, or long running with no cooling demand.
- Check coil and supply first, then strip the valve — most leaks are dirt or a weak spring, not a failed coil.
- Renew the seat and spring, clean the orifice and prove shut before the system is put back on load.
Surveyor follow-up: box warm with the coil proved live and the valve humming — seat, spring or orifice first?
Full theory: Refrigeration Principles and the Vapour Compression Cycle -
38 Maintenance of Hydraulic System
Answer
Hydraulic upkeep is cleanliness and pressure: keep the oil right, the filters clean, the leaks stopped and the accumulators correct.
- Maintain pressure, oil tightness and cleanliness of the system — the three things that decide whether it works.
- Check oil level, condition and temperature, renewing filters and suction strainers on schedule.
- Trace and stop leaks at glands, cylinders and hose unions before they cost oil and heat.
- Keep governor and control springs in good order, since the hydraulic side of a governor is what holds the setting.
Surveyor follow-up: oil heating fast with the level steady and the strainer clean — leak, relief setting or pump efficiency first?
Full theory: Hydraulic Drives for Deck Machinery — Fluid, Pumps and Circuits -
39 Master valve if stuck then what will happen (tell about relief valve on the line
Answer
A stuck master valve traps pressure behind it — which is exactly why the line carries a relief valve to vent the excess.
- If the master valve sticks shut, pressure builds in the line downstream and can burst pipework or damage actuators.
- The relief valve on the line lifts and discharges the excess, which is the last protection before the pipe fails.
- Stuck open is worse for control: the system cannot hold pressure and the pump delivers to nothing.
- Prove both the master valve and the relief on schedule, and never isolate a line that still has a live pump feeding it.
Surveyor follow-up: master valve stuck open with the relief lifting hourly — valve, pump or relief setting first?
Full theory: Quick Closing Valve: Construction & Working -
40 Piping on ships
Answer
A ship’s pipe runs five services: bilge, ballast, fuel, fresh water and sea water — each with its own pump, chest and isolation rules.
- Bilge lines run outboard with non-return valves so no watertight compartment communicates with another.
- Ballast lines are kept out of double bottoms where possible, led through pipe tunnels in way of deep tanks.
- Only two pipes pass the collision bulkhead below the bulkhead deck, each with a screw-down valve operated from above deck.
- Sea-water and cooling systems draw from sea chests with strainers, MGPS and change-over, feeding every cooler on board.
Surveyor follow-up: third pipe found through the collision bulkhead below deck — which service, and what rule does it break?
Full theory: Ship Pipelines — Seawater, Bilge, Ballast & Fuel Systems -
41 Purpose of solenoid valve in AC system
Answer
Solenoids are electrical on-off taps: they let the thermostat cut refrigerant to a space, and pump the plant down or off as ordered.
- An electrically operated shut-off in the liquid line, plunger on the orifice or acting as a pilot through a servo.
- Usually energise to open, de-energise to close, so a lost signal shuts the valve by itself.
- In refrigeration they sit before the expansion valve, opened by the thermostat and shut when the space is cool enough.
- Sizes beyond small bore use the solenoid as a pilot on a main servo — the principle stays, the size changes.
Surveyor follow-up: space overcooling with the solenoid proved open and the thermostat cool — valve, sensor or charge first?
Full theory: Refrigeration Principles and the Vapour Compression Cycle -
42 Pv valve and Pv breaker Purpose and value of Both
Answer
Both protect the tank top from pressure or vacuum — the breather continuously, the P/V valve at the loads it cannot pass.
- P/V breather purpose: pass tank breathing gases steadily with the least possible pressure difference.
- P/V valve purpose: pass the larger volumes that filling, emptying, heating or sloshing throw at the tank.
- Values are set low — even modest pressures over a large tank area give a big total load on the deck or side plating.
- Quote both settings and the damage case: over-pressure distends the top, vacuum collapses it inward.
Surveyor follow-up: tank top dished with the breather stuck shut — reset valves, relieve vacuum or survey the plating?
Full theory: Ship Pipelines — Seawater, Bilge, Ballast & Fuel Systems -
43 Pv valve and pv breaker and set points. Too many cross
Answer
P/V valves protect tank tops, breather valves protect hulls — and crossing their set points in a layout is the design flaw to spot.
- P/V valves are set to stop pressure or vacuum damaging tank plating; breather valves are lighter-duty units for hull tanks.
- Both settings are low because even small pressure over a large tank area gives a large total load.
- Where several V/U tanks are cross-connected, the weakest protection governs — you cannot set each tank independently.
- Quote both devices, both settings and the cross-connection, then say which one is actually protecting the plating.
Surveyor follow-up: cross-connected tanks with one breather stuck shut and rising pressure — relieve, isolate or vent which tank?
Full theory: Ship Pipelines — Seawater, Bilge, Ballast & Fuel Systems -
44 Quick closing valve mechanism
Also asked: “Hydraulic operated quick closing valves”
Answer
Quick-closing valves shut on a rate, not a command: spring, oil pilot or gravity drives the closure so steam is cut fast and repeatably.
- A spring-loaded arrangement drives the valve closed, with a dashpot or oil pilot setting the closing speed.
- On steam turbine control the emergency stop valve seats on oil pressure — losing that oil opens it and dumps steam to drain.
- The same oil-pressure-loss, governor-overspeed and hand-emergency trip each emergency valve in the system.
- Test the mechanism, not just the handwheel: prove the closing time and the trip that should fire it.
Surveyor follow-up: emergency stop valve found open after an oil-pressure trip — reset, investigate the trip, or both first?
Full theory: Quick Closing Valve: Construction & Working -
45 Quick closing valve overhaul
Also asked: “overhauling of quick closing vave”
Answer
Overhaul quick-closing valves as if the fire is coming: strip, inspect, lap, rebuild, prove timing and swap in the tested spare.
- Back off the jam screw, remove cover nuts and cover, then the yoke, keeping the parts in order.
- Discard cover and seat gaskets, clean the seating surfaces and inspect seats for burring, wire drawing and breakage.
- Lap the valve into its seat, renew the stem, gland and packing, and check the closing-speed adjustment and spring.
- Reassemble, prove the closing rate on the bench, and fit the overhauled spare so no valve is out of service on the engine.
Surveyor follow-up: valve reassembled with the closing time unproved and the spare on the bench — fit or prove first?
Full theory: Quick Closing Valve: Construction & Working -
46 Relief valve in fire ext
Answer
A CO₂ manifold relief valve is the pressure safety net: set near 180 bar, it vents to atmosphere outside the CO₂ room.
- It releases manifold pressure to the atmosphere when bottles discharge but the master valve is still closed.
- Set pressure is around 180 bar, varying with the system design and the applicable regulations.
- Without it a closed master valve with live bottles behind it becomes a pressure vessel with nobody watching.
- Prove the setting and the discharge route on schedule, and keep the vent clear of any place gas could collect.
Surveyor follow-up: manifold at full pressure with the relief isolated and master valve stuck shut — open the master or vent first?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
47 Scavenge air duct flap valve before engine is to be shut
Answer
The scavenge-air duct damper closes before the engine stops so air cannot reverse through the trunk into a hot engine.
- Closing the flap isolates the trunk from the turbocharger and atmosphere while the engine is still turning.
- With it open, shutting down can draw hot exhaust gas back through the air path and dry the turbocharger bearings.
- The same isolation is why blow-through and trunk purging are sequenced around the damper position.
- Prove the damper operates and interlocks if fitted, and record its position in the shutdown routine.
Surveyor follow-up: damper found wide open at shutdown with the engine stopped for two hours — reposition, inspect or accept?
Full theory: Marine Turbochargers: Aerodynamics, Bearings, Washing & Surge Mitigation -
48 The three main components of a valve are the body, valve seats and the shafts or stems; these will be considered separately. It should be noted, however, in a system with a nominal seawater velocity of a few meters-per-s
Also asked: “The three main components of a valve are the body, valve seats and the shafts or stems; these will be considered separately. It should be noted, however, in a system with a nominal seawater velocity of a few meters-per-second flow through the valve, that the valve, depending on its design, may give rise to turbulence and much higher local velocities, particularly when the valves are used for throt”
Answer
Every valve is a body, a seat and a stem — and in seawater the seat face is the part that dies first.
- The body carries the pressure and contains the flow path; seat rings give the valve its shut-off surface.
- The stem or shaft transmits motion from the handwheel, actuator or solenoid to the disc.
- Even a modest nominal seawater velocity erodes seat faces, so materials and trim are chosen for that service.
- Name all three with the failure each one produces — body cracked, seat eroded, stem bent or gland leaking.
Surveyor follow-up: valve weeping with the body sound and the stem straight — seat erosion, gland or misalignment first?
Full theory: Globe, Gate & Non-Return (SDNR) Valves: Working, Troubleshooting & Overhaul -
49 The valve of voltage generated in the megger
Answer
Meggers are guarded by their own valves: a discharge valve to discharge the test voltage, and isolation when not in use.
- The discharge valve vents the test voltage from the instrument capacitor so the set is safe to handle when unplugged.
- Connected to the circuit under test it stays shut, applying the full test voltage between conductor and earth.
- Never disconnect a megger from a live circuit with the voltage applied — the set itself can be destroyed.
- Range from 500 V upward; the valve is why a megger is safe to carry and why its failure is the first thing to check.
Surveyor follow-up: megger reading nonsense with the discharge valve seized open — valve, test lead or the cable being tested?
Full theory: Marine High Voltage (HV) Installations — 3.3 kV, 6.6 kV & 11 kV Switchgear and Safety -
50 WHAT TO DO IF VALVE SEAT DAMAGED?
Answer
A damaged seat is dressed if it is still there and renewed if it is not: lap lightly, then regrind only as a last step.
- Light damage is lapped on a surface plate with the bonnet rotated on the seat, coarse compound first, then finer.
- Deeper damage is cut on a lathe — but take the minimum metal, or the flexible metallic gasket will not fit.
- Verify with blue marking compound on the disc turned lightly against the seat to read the contact pattern.
- If the seat ring, the disc face or the body is cracked, replace the part — no amount of lapping saves a fracture.
Surveyor follow-up: third lapping of the same seat with the contact still reading wide — keep lapping, regrind or renew?
Full theory: Globe, Gate & Non-Return (SDNR) Valves: Working, Troubleshooting & Overhaul -
51 Wear short sleeve boiler suits, if possible, or overall with snugly fitting cuffs if long sleeve
Answer
Dress for the job: boiler suits protect from radiated heat, with snug cuffs and nothing loose near a burner or a hot door.
- Short-sleeve boiler suits where possible, otherwise overalls with snugly fitting cuffs to keep cloth off hot surfaces.
- Nothing loose, nothing trailing — sleeves, ties and towels near a fired boiler catch fire before you notice.
- Add eye, face and hand protection for gauge work, blowdown and fire fighting, with footwear that will not slip on wet decks.
- Dress is the first control in the fire equation: the correct suit is what keeps a small mistake from becoming a burn.
Surveyor follow-up: engineer sent up with a loose towel round the neck to read a gauge — send him back or continue?
Full theory: Boiler Safety Devices and Emergency Response -
52 Why do you open inboard valve first, what happens if opened later ? What is specific name of wear that takes place at valve ?
Answer
Inboard first gives the water somewhere to go; opened late, the sea chest and the valve face take the full pressure shock.
- Opening the inboard valve first establishes flow through the chest and line before the sea chest valve admits the sea.
- Open the sea chest first and pressure builds against a closed line — the valve body and seat take the load unaided.
- The wear this causes at the valve is erosion, with cavitation added where velocity and pressure drop across a seat.
- High-velocity discharge past a partly open valve also strips seat faces — the same reason the sequence is written down.
Surveyor follow-up: sea chest opened first on a cooling line and the valve later found eroded — sequence, seat or strainer first?
Full theory: Globe, Gate & Non-Return (SDNR) Valves: Working, Troubleshooting & Overhaul -
53 Why solenoid valve if tev is there
Answer
The expansion valve meters and the solenoid isolates: one controls flow, the other simply shuts the refrigerant off.
- The thermostatic expansion valve controls how much refrigerant enters — it never closes the line entirely.
- The solenoid in the liquid line just before it is an electric on-off tap operated by the thermostat.
- It shuts supply when the space is at its lower set point and reconnects it when the temperature rises above the upper.
- Together they let the box hold temperature without the compressor pumping a full charge of refrigerant into a cold room.
Surveyor follow-up: solenoid proved open with the box at temperature and the TEV wide — thermostat, sensing bulb or valve first?
Full theory: Refrigeration Principles and the Vapour Compression Cycle -
54 arrangements provided to avoid excess pressure buildup inside scavenger air receiver? lifting pressure of the relief valve?
Also asked: “• arrangements provided to avoid excess pressure buildup inside scavenger air receiver? lifting pressure of the relief valve?”
Answer
The scavenge air receiver is protected by relief valves: they lift at a set pressure and dump the excess air rather than burst the receiver.
- Relief valves on the receiver vent surplus pressure so the receiver shell never carries more than its design pressure.
- The lift pressure is set below the receiver’s allowable working pressure, with margin for the highest expected running pressure.
- Pressure rise on a positive-displacement scavenge pump discharge is the usual cause — the pump absorbs more power and delivers less air.
- Prove the lift on the bench with calibrated gauges and log the setting; a relief found stuck is the one the day needs.
Surveyor follow-up: receiver relief lifted twice this voyage with pumps and filter proved normal — check setting, or find the rise?
Full theory: Marine Turbochargers: Aerodynamics, Bearings, Washing & Surge Mitigation -
55 exhaust valve checks
Also asked: “checks on valves”
Answer
Exhaust valves are checked for sealing, clearance and face condition — the three that cost compression if missed.
- Lap the valve into its seat on a machine and prove tightness with the classic three-lap or kerosene test.
- Check clearance and lift; too little opens early and closes late, too much keeps gas burning past the face.
- Inspect for concave burn-through from high-temperature corrosion and for pitting on the valve head underside.
- Excess gas past a leaking face burns the valve, drops compression and hides the real fault behind a burnt valve.
Surveyor follow-up: valve lapped and still burning past the face with clearance on figures — seat, guide or timing first?
Full theory: The Valve Gear and Fuel Injection — Valves, Camshaft Drive, Pumps and Injectors -
56 quick closing valve on mixing/vent tank
Answer
On the mixing/vent tank the quick-closing valve stops fuel and steam mixing paths fast, isolating one side of the boiler.
- Fitted so one boiler can be isolated from the shared mixing header without shutting the whole steam system.
- Its closing speed matters: slow closure risks a water hammer through the header on a light load.
- Test the mechanism and the closing time, not just the hand position, and prove the interlock with the neighbouring boiler.
- Keep it accessible — a quick-closing valve behind insulation is no valve at the moment it is needed.
Surveyor follow-up: valve isolated for cleaning and found seized with the twin boiler on load — which boiler carries the risk first?
Full theory: Quick Closing Valve: Construction & Working -
57 valve and exhaust valve tests
Also asked: “Fuel valve tests”
Answer
Two tests, two answers: the valve is proved tight, the exhaust valve proved seated, and both proved while the engine runs.
- Valve: lifted and lowered, checked tight on the seat, gland repacked and the motion smooth through full travel.
- Exhaust valve: lift proved by feeler or indicator, then a running check watching lift and any gas passing the seat.
- Record both with the engine stopped and cold for the setting, then hot and running for the behaviour.
- A valve that is only proved cold is a valve whose hot clearance nobody has ever seen.
Surveyor follow-up: valve tight cold but weeping hot at full load — thermal bind, gland or seat material first?
Full theory: The Valve Gear and Fuel Injection — Valves, Camshaft Drive, Pumps and Injectors
Source: 123 written papers and surveyor oral banks, 24,613 entries, merged into 17,210 topics. Ticks are stored on this device only.