Purifier / Clarifier — Most Asked Questions
19 questions asked about purifier / clarifier across the General and Fn 6 and Fn 3 papers, heaviest first. 2 of them are must-master.
Learn the system first
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1 purifier overflow reason?
Also asked: “purifier overflowing reason”, “Causes of purifier overflow”
Answer
A purifier overflows when the oil-water interface leaves its designed position — wrong disc, wrong temperature, too much feed, or a bowl that never sealed.
- Check in order: gravity-disc size, excessive throughput, feed-oil temperature off mark, low operating-water level, missing sealing water, bowl not closed, damaged seal ring.
- Troubleshooting adds: heavy sludge bowl, changed oil density, and aged or cut bowl/hood sealing rings.
- First action on overflow alarm: acknowledge, swing the 3-way inlet valve to recirculation, then verify feed temperature, rpm (by amperage) and feed rate.
- Only after correcting rpm and conditions: desludge, restart and watch the clean-oil outlet before sending it to the service tank.
Surveyor follow-up: overflow right after a bunker stem with the same disc and settings — what changed, and how do you pick the fix?
Full theory: Purifier Troubleshooting: Fault Diagnosis and Fixes -
2 How to change purifier to clarifier?
Also asked: “How to convert purifier to clarifier”, “how to change purifier to clraifier”
Answer
Converting to clarifier blinds the water outlet: out with the gravity disc, in with the blind disc and neck bush, sealing water shut.
- Remove the gravity disc and fit the blind (solid) separation disc — no holes — or, if none is carried, the bottom-most separation disc without holes.
- Fit the top disc without neck and fit a neck bush; remove the water pairing.
- Shut off the sealing water — a clarifier has no water seal to hold.
- Remember the trade: a clarifier polishes solids and cat fines from already-dry oil but cannot remove water — never leave sealing water cracked open or oil goes to the sludge tank.
Surveyor follow-up: after conversion the clean-oil outlet shows water — which step was skipped?
Full theory: Purifier Operations: Start-Up, Running & Conditioning -
3 Diff between clarifier and purifier
Also asked: “Diffrnce bw purifier vs clarifier”, “Purifier and clarifier constructional difference”, “Purifier vs clarifier”
Answer
A purifier removes water and solids with a water seal; a clarifier removes solids only with the water outlet blinded.
- Purifier runs a gravity disc with holes and sealing water holding the oil-water interface in place.
- Clarifier fits a blind disc without holes plus a sealing ring and neck bush, with sealing water shut off.
- Disc stacks differ: clarifier discs often lack feed holes, or a hole-less disc sits at the stack bottom.
- Use follows the oil: wet dirty oil through the purifier first, dry oil polished for cat fines through the clarifier.
Surveyor follow-up: clean outlet shows water after conversion to clarifier — which step was skipped?
Full theory: Purifier Principle: Centrifugal Separation & Stokes' Law -
4 purifier not picking speed
Also asked: “)purifier speed not coming up”
Answer
A purifier that will not reach speed is starved, dragging or single-phased: electrics, clutch, bowl and brake in that order.
- Electrics first: single-phasing, low voltage or overloaded motor with the wrong current on one leg.
- Drive next: worn friction clutch and pads, misaligned vertical and horizontal shafts, worn bearings.
- Bowl and sump: excess sludge unbalancing the bowl, sump level too high, brake still touching.
- Back-pressure and feed faults behind it: closed service-tank valve, dead solenoid, blocked strainer, lifting feed relief.
Surveyor follow-up: amps normal with speed low — clutch, bearings or brake, and what do you feel for first?
Full theory: Purifier Operations: Start-Up, Running & Conditioning -
5 purifier not attaining RPM ?
Also asked: “Purifier not attaining rpm after overhaul”, “Purifier not picking the rpm what are the Reasons for that”
Answer
A purifier stuck below speed drags somewhere: friction pads, brake, bowl height or feed back-pressure holding it down.
- Friction pads and clutch faces worn or oily slip instead of driving; brake dragging caps the top speed.
- Bowl height shifted by bearing wear misaligns desludge ports so water never leaves and sludge never drops.
- Feed faults behind it: relief lifting, strainer choked, back-pressure high from a shut service-tank valve.
- Prove electrics first — single phase and low volts mimic every mechanical fault — then open the drive.
Surveyor follow-up: speed builds then sags under feed — drive, bowl or back-pressure, and what gauge proves it?
Full theory: Purifier Troubleshooting: Fault Diagnosis and Fixes -
6 Purifier to clarifier
Also asked: “Purifier to clarifier changeover”
Answer
Convert by blinding the water side: hole-less discs in, sealing water off, neck bush fitted.
- Swap gravity discs for blind discs without holes, or the bottom separation disc if no blind set exists.
- Fit the neckless top disc with neck bush and lift the water pairing out.
- Shut sealing water — a clarifier holds no water seal to keep.
- Remember the trade: solids and cat fines polished, water untouched — feed dry oil only.
Surveyor follow-up: clean outlet shows water after conversion — which step was skipped?
Full theory: Purifier Operations: Start-Up, Running & Conditioning -
7 Purifier vibration reason
Also asked: “Purifier vibrating reasons”
Answer
Purifier shake is imbalance, bearings or drive: sludge lumps, worn shafts, tired springs and loose foundations.
- Uneven sludge distribution and critical-speed passing shake hardest on stopping and starting.
- Worn vertical-shaft bearings and tired buffer springs let horizontal vibration run free.
- Worm-and-wheel stress peaks as the small gear drives the big one on stopping — brakes save the teeth.
- Loose foundation bolts and shifted bowl height finish the shake list before electrics.
Surveyor follow-up: smooth running, violent stopping shake — sludge, springs or gears, and what do you check first?
Full theory: Purifier Troubleshooting: Fault Diagnosis and Fixes -
8 Purifier manual desludging procedure?
Answer
Manual desludge stops, displaces and opens: displace oil to service, drop the slide, sling sludge, reclose and restart by the book.
- Displace purified oil to the service tank with water, then stop closing water and pulse opening water to drop the slide.
- Sludge ports open as the bowl drops — sludge flung outward to the sludge outlet for the timed seconds.
- Re-admit lifting water to reseal the bowl edge, then water and oil in sequence to restart purification.
- Self-cleaners desludge running; manual bowls stop, brake past critical speed, open, clean the sludge space and rebuild.
Surveyor follow-up: oil to the sludge tank after desludge — bowl height, seal ring or timing, and what proves it?
Full theory: Purifier Maintenance: Cleaning, Inspection & Overhaul -
9 A) Define role played by the gravity disc and the way to determine it's size for effective purification
Also asked: “A) Define role played by the gravity disc and the way to determine it’s size for effective purification”
Answer
The gravity disc parks the oil-water interface: bore sized by oil density at 15 degrees on the maker nomogram, proved by outlets.
- Bigger bore pushes the interface outward for efficient cleaning without oil down the water outlet.
- Too big breaks the seal and oils the water side; too small floats water out with the clean oil.
- Read the first trial bore straight off the nomogram at measured 15-degree density.
- Prove in service with the largest bore that holds the seal dry — seawater in fuel moves the answer.
Surveyor follow-up: water in clean oil with the nomogram disc fitted — bigger, smaller or hotter, and why?
Full theory: Purifier Principle: Centrifugal Separation & Stokes' Law -
10 If excessive sludging should occur, giving evidence of incompatibility, the fuel should be separated at the slowest possible rate using purifiers in parallel. When drawing from a fuel tank for the first time, it is very
Also asked: “• If excessive sludging should occur, giving evidence of incompatibility, the fuel should be separated at the slowest possible rate using purifiers in parallel. When drawing from a fuel tank for the first time, it is very important that a careful watch be kept on the purifier for the first twelve”
Answer
Sludging new bunkers means incompatible fuel: segregate tanks, run purifiers slow and parallel, watch the first twelve hours.
- Keep suspect stems segregated — never blend unknown bunkers into settled tanks.
- Separate at minimum throughput with purifiers paralleled for maximum bowl time each.
- Watch new-tank draws hard for the first twelve hours with filters and sludge tanks ready.
- Sea contamination, temperature swings and bacterial growth join incompatibility on the sludge list.
Surveyor follow-up: sludge rising on a new stem with settings correct — segregate, slow or heat, and what first?
Full theory: Purifier Operations: Start-Up, Running & Conditioning -
11 If the fuel density is marginally over the 991 kg/m3 limit and the water content is low, both centrifuges are used as clarifiers for better cleaning
Also asked: “• If the fuel density is marginally over the 991 kg/m3 limit and the water content is low, both centrifuges are used as clarifiers for better cleaning”
Answer
Dense dry fuel defeats purifier gravity: run both machines as clarifiers and polish solids instead of chasing water.
- Past 991 kg per cubic metre the density gap nearly vanishes — interfaces will not hold.
- With water low, solids and cat fines matter more than separation — clarifiers catch those.
- Blind discs in, sealing water off, both bowls polishing in series or parallel.
- Prove by outlet clarity and filter differentials, not by water figures that cannot exist.
Surveyor follow-up: water appears later with both machines clarifying — convert back, heat or slow, and what first?
Full theory: Purifier Operations: Start-Up, Running & Conditioning -
12 To obtain optimum centrifugal separation, reduce viscosity of fuel oil by heating it before centrifuging. Allow the fuel oil to remain in the centrifuge bowl as long as possible by adjusting to minimum throughput
Also asked: “• To obtain optimum centrifugal separation, reduce viscosity of fuel oil by heating it before centrifuging. Allow the fuel oil to remain in the centrifuge bowl as long as possible by adjusting to minimum throughput”
Answer
Best separation is hot, slow and long: heat to thin, trickle for bowl time, keep the interface parked.
- Heat toward 24 cSt separation viscosity — hot thin oil sheds water and grit it cold oil keeps.
- Minimum throughput holds oil in the bowl longest for the centrifugal field to work.
- Gravity-disc bore and temperature together park the interface where outlets run clean.
- High main-engine flows beat settling tanks alone — that is why centrifuges exist.
Surveyor follow-up: outlets dirty with heat and flow correct — disc, bowl or feed, and what do you change first?
Full theory: Purifier Principle: Centrifugal Separation & Stokes' Law -
13 purifier starting procedure
Also asked: “Purifier start procedure”
Answer
Start purifiers by speed, seal, feed: bowl to revs, water seal made, oil in slow with outlets watched.
- Spin the bowl to rated revs — past ten minutes without speed means stop and read the friction blocks.
- Make the water seal before oil, then feed slow watching clean and water outlets for the interface.
- Vibration at low-speed passing is transient and normal; sustained shake is sludge, bearings or drive.
- Stop by the book with displacement water to service, slide dropped, ports proved, motor off after coast-down.
Surveyor follow-up: bowl at speed with oil to the sludge tank — seal, disc or bowl height, and what first?
Full theory: Purifier Operations: Start-Up, Running & Conditioning -
14 Explain briefly procedure for maintaining vertical shaft of centrifuge, name the parts with a simple sketch b.) Briefly explain what is the purpose of gravity disc in a purifier? Ans. The vertical shaft parts are dismant
Also asked: “Explain briefly procedure for maintaining vertical shaft of centrifuge, name the parts with a simple sketch b.) Briefly explain what is the purpose of gravity disc in a purifier? Ans. The vertical shaft parts are dismantled once in 8000 hours. Usually, bearings, bearing housing and bearing springs are checked and renewed as appropriate. Sealing rings and o-rings are renewed as per maker’s recommen”
Answer
The vertical shaft comes down to bearings, spring seat and locking nut — strip it in order, and the gravity disc sets where oil and water meet.
- Strip the spring seat, spring and retainer from the bearing housing, then screw push bolts into the bearing case and pull it out with the spacer.
- Assemble the jacks and push bolts, then pull the bearing case, cover, collar, roller bearing and ball bearing together.
- Remove the lock washer and lock nut of the upper bearing with a hook spanner, and lift the ball bearing out by tapping the inner race only.
- The gravity disc sets the location of the oil-water interface, sized from separation temperature, oil density and required throughput.
Surveyor follow-up: bearing races scored after tapping the outer race on reassembly — which race should the drift touch, and why?
Full theory: Purifier Maintenance: Cleaning, Inspection & Overhaul -
15 Purifier gravity disc
Answer
The gravity disc decides where the oil-water interface sits in the bowl: wrong size and the purifier either floods or fails to clean.
- An important part of the purifier that sets the oil-water interface line, which varies with the maker’s design.
- Size is chosen from separation temperature, the density of the oil at that temperature and the desired throughput, using a nomogram.
- Too small a disc raises the interface and the oil carries water; too large lowers it and the water carries oil out with the clean oil.
- That is the first check on an overflowing purifier — before blaming the bowl, the clutch or the feed temperature.
Surveyor follow-up: purifier overflowing with the disc correct for the oil — is the temperature, the throughput or the bowl next?
Full theory: Purifier Maintenance: Cleaning, Inspection & Overhaul -
16 Purifier vibrating while starting, all reasons
Also asked: “Purifier vibrating during starting. Reasons”
Answer
A purifier that shakes on starting is either out of balance or badly coupled — and both destroy bearings if ignored.
- Friction clutch slipping or worn gives erratic speed and a vibration that changes with the load.
- Vertical and horizontal shafts out of alignment, or a worn bowl bearing, produce a heavy steady shake.
- Excessive sludge in the bowl unbalances it as it spins up, and a high sump level adds to the unbalance.
- Motor single phasing, low voltage or overload, a faulty solenoid, or back pressure from a closed service valve all disturb the start.
Surveyor follow-up: purifier shaking on start with the clutch and alignment proven — is it sludge, the sump level or the motor supply?
Full theory: Purifier Maintenance: Cleaning, Inspection & Overhaul -
17 Purifire room fire as wathckeeper actions
Answer
A purifier room fire is a fuel fire: alarm, isolate the oil, close the room down and cool from outside before flooding.
- Sound the alarm, inform bridge and chief engineer, and identify the size, location and whether the purifier must be stopped.
- Isolate the fuel feed and the heating to the purifier, and stop the separator from outside the engine room if provided.
- Close doors, vents and flaps to restrict the fire, keeping the room sealed while the purifier is stopped.
- Cool boundaries from outside and use the fixed system if the fire cannot be contained — enter only with a permit and breathing sets.
Surveyor follow-up: purifier room alight with the fuel valve still open and the room already sealed — isolate or enter first?
Full theory: Purifier Maintenance: Cleaning, Inspection & Overhaul -
18 Purpose of gravity disc in a purifier Gravity Disk in Purifier alters the location of the oil-water interface and is responsible for creating an interface between the oil and water. And further, the Interface can be shif
Also asked: “Purpose of gravity disc in a purifier Gravity Disk in Purifier alters the location of the oil-water interface and is responsible for creating an interface between the oil and water. And further, the Interface can be shifted inwards or outwards with the correct selection of the gravity disk in your purifier. And With the proper selection of the gravity disk, the efficiency of the separation can als”
Answer
The gravity disc sets where the oil meets the water inside the bowl: it is the difference between a clean separator and an overflowing one.
- The disk alters the location of the oil-water interface and creates the interface between the oil and the water.
- The interface can be shifted within the bowl by changing the disc, and that shift decides what is carried out with the separated oil.
- Sized against separation temperature, oil density and required throughput, it is the first check on a purifier that will not clean.
- Get it wrong in either direction and the machine either passes water with the oil or dumps oil with the water.
Surveyor follow-up: disc oversized for the new oil grade with the machine fouling — resize the disc or the feed temperature?
Full theory: Purifier Maintenance: Cleaning, Inspection & Overhaul -
19 Y break is used in purifier?
Source: 123 written papers and surveyor oral banks, 24,613 entries, merged into 17,210 topics. Ticks are stored on this device only.