Prufiers and Clarifiers

SEPARATORS
• PRUFIER
• CLARIFIER
NEJAT ÖZTEZCAN
CHIEF ENGINEER
Nejat Öztezcan Chief Engineer 1

SEPARATION
Separation as a means of removing impurities from a fuel can be
undertaken by means of gravity in a settling tank or by means of
centrifuging the fuel.
Both methods work on the same principles that by subjecting the
fuel to a constant force, the denser components of the fuel
i.e water and dirt will be separated from the lighter components
i.e. the fuel itself.
Both fuel oils and lubricating oils require treatment before
passing to the engine.

If an oily water mix is placed into a tank then separation of the
two parts will begin with the lighter element rising to the top.
The rate the separations occurs is governed by several factors
including the difference in specific gravities and the force of
gravity acting upon it.
For mixes placed into a settling tank there is little that can be done
about the gravity but the difference in the specific gravities can be
increased by heating.
This because water density changes at a much reduced rate when
compared to oil.
A wide shallow tank will increase the rate of clarification over a tall
thin tank

When a volume of light oil is placed into a tank contain a weir and a
quantity of water the fluids will tend to arrange themselves as shown
above. The height of the water in the weir rises to a point governed
by the volume ( and thereby relative height) and specific gravity of
the light oil.
Knowing this it is possible to form a rudimentary purification system
GRAVITY SEPARATION

As a oil/water mix is fed into the tank separation begins with heavy
particulates falling to the base of the tank along with water which
joins the other water excess overflowing the heavy phase weir.
Hopefully clear oil passes over the light phase weir. The problem
arises that to ensure their is sufficient time to allow for full
separation of the oily mix the flow would have to be very small
relative to the size of the tank.
interface

Efficiency of gravity separation are dependent on a number of
factors;
1. Time
2. Speed
3. Distance
4. Relative density
5. Particle size and shape
6. Liberation
Distance

Centrifuging
Centrifuging is the process by which the effects of gravity can be
amplified by the use of centrifugal force to the extent that the
separation process becomes rapid and continuous.
The principle of operation of the centrifuge is simple. When a bowl
containing impure fuel is rotated, centrifugal forces will throw any
item with density greater than the fuel oil density (solids and free
water) to the periphery of the bowl.
Centrifugal separators used for the separation of two liquids of
different densities (fuel and water) are known as purifiers and those
used for separating solid impurities are known as clarifiers.
Purifiers will also remove some solids and clarifiers will also remove
small quantities of water.

The centrifuge includes parts that rotate at high speed. This
means that:
• Kinetic energy is high
• Great forces are generated
• Stopping time is long
Rotating parts are carefully balanced to reduce undesired
vibrations that can cause a breakdown.
If excessive vibration occurs, stop the seperator.

Clean Oil
Outlet
Water Outlet
Gravity disk

Principle of separation in centrifuge containing angled plate stack

Which factors have an effect on centrifugation :
•Density difference
•Temperature/viscosity
•Distance of particles displacement
•Rotation speed
•Gravity disc
•Back Pressure of output
•Rate of throughput (oil feed)

There are normally two types based on the application:
1) Purifier: When a centrifuge is arranged for separating two liquids
of different densities, for e.g. water from oil, it is known as a purifier.
2) Clarifier: When a centrifugal is arranged to remove only impurities
and small amount of water, it is called as clarifier.

The basic operations of clarifier and purifier are:
It contains stack of disk numbering up to 150 and are
separated from each other by very small gap.
A series of holes are aligned in each disk near the
outside edge which permits the entry of dirty oil.

- Due to difference in gravity and centrifugal force, the heavier
impure liquid (water) and particles moves outside and lighter
clean oil flows inwards and get separated.
- The collected sludge and impurity can be discharged
continuously or at a time intervals, depending upon the
construction, automation and system incorporated.

Purifier
• When a centrifuge is set up as a purifier, a second outlet pipe
is used for discharging water.
• In the fuel oil purifier, the untreated fuel contains a mixture of
oil, solids and water, which the centrifuge separates into three
layers.

Purifier Operation

• As marine fuel oil normally contains a small quantity of water, it
is necessary to prime the bowl each time that it is run, otherwise
all the oil will pass over the water outlet side to waste.
• The water outlet is at greater radius than that of the fuel. Within
the water outlet there is a gravity disc, which controls the radial
position of the fuel water interface
• A set of gravity discs is supplied with each machine and the
optimum size to be fitted depends on the density of the
untreated oil.
PRUFIER

• If it is set as a purifier, the free water is continuously
discharged, therefore, the particulate matter will consist of
solid material.
• In older machines it is necessary to stop the centrifuge to
manually clean the bowl and disc stack, however, the majority
of machines today can discharge the bowl contents while the
centrifuge is running.
• When the fuel centrifuge is operating, particulate matter will
accumulate on the walls of the bowl. If the centrifuge is set as
a clarifier, the particulate matter will be a combination of water
and solid material.

Purification process is based on types of purifier used :
(1) Non-continuous operation type purifier
(2) Continuous operation type purifier.
• In Non-continuous operation type purifier, sludge is cleaned
manually after operating some time.
• In Continuous operation type purifier, sludge is cleaned
automatically at regular intervals, it is also called as self-
cleaning purifier. Non-continuous operation type is still suitable
for lube oil system.

Safeties in Purifier
• Low pressure switch in the outlet of clean oil
• Emergency brakes - for speed regulation
• High pressure switch in the clean oil outlet
• Water transducer to avoid water mixing

The following is compulsory for safe operation:
1. Never start up a separator before the bowl is completely assembled, and all
fastenings securely tightened.
2. Never discharge a vibrating separator. Always stop with the emergency stop
button.
3. Never begin to disassemble a separator before it has come to a complete
standstill.
4. Always set the discharge intervals according to instructions in the
instruction book.
5. Never ignore alarms. Always eliminate the cause before resuming
operation.
6. Never use the separator for other liquids than those specified by
manufactor.
7. Never operate a separator with a different power supply frequency than
stated on the machine plate.
8. Ensure that enough conditioning water is added before discharge, as
described in the instruction book.
9. Clean the operating system regularly to avoid sludge discharge malfunction.
10.Ensure that personnel are fully trained and competent in installation,
operation, maintenance, and emergency procedures.

The following factors are of importance when
understanding the function of the purifier
 Increasing the Specific gravity of the oil will tend to push
the interface outlet and cause overflow from the heavy
phase outlet untill the equilibrium is restored.
 Reducing the Specific gravity of the oil will tend to bring the
interface towards the axis, this reduces the force of
separation on the oil mix and reduces the efficiency of the
unit possibly leading to contaminants and water carryover
with the light phase outlet

The "gravity" disc are changeable on virtually all purifers.
Their centre bore is governed by the sp.gravity of the oil
being centrifuged.
The largest bore should be used without risking overflow.
The flow rate of a purifer should be set to optimise removal
of whole system impurities.
The lower the oil feed the greater the time for impurity
removal and the more efficient the purification.

Important
•Interface : Less interface means (water + oil) comes out from water
side. More interface means (water + sealing water) comes out,
overflowing from water side.
•If oil density increases, Gravity Disc size decreases and If oil density
decreases, Gravity Disc size increases.
• (Without Nomogram) If don’t know which size of gravity disc to be
used : Then use bigger gravity disc first – then one down size gravity
disc – then one down size gravity disc, When purifier stops
overflowing, that is the correct size of Gravity Disc.

PARTS OF A PURIFIER

Basic components of the centrifuge are as follows:
• Exterior framework:
The exterior frame work is normally made up of caste iron
which supports the internal bowl and disk parts and carries
water line, feed line and outlet line connections.
• Bowl and disk:
There are bowls inside the frame, which can be a solid
assembly operating non continuous and have space enough to
retain the separated sludge.
There can also be an arrangement in which the upper and
lower parts are separate for discharging the accumulated
sludge by a continuous operation. These parts are normally
made up of high tension stainless steel.

Vertical shaft:
The Vertical shaft is used to transform the electrical motor output into
rotational motion for rotating the bowl in high speed through spur gear
and horizontal shaft or belt. material used for vertical shaft construction
is an alloy of steel.
Horizontal shaft or belt drive:
The electrical motor drives the horizontal shaft through clutch pads and is
used for transmitting the rotational motion to bowl assembly. A special
belt having elastic character is used in some models in place of horizontal
shaft, thus removing the use of the gear assembly. The horizontal shaft
material is a special alloy of steel.
Attached Gear pump:
A general construction of centrifuge consists of a horizontal shaft driven
attached supply or discharge gear pump. In some system an external
supply pump may be installed in place of the attached pump.

Spur gear:
A spur gear is placed between the horizontal and vertical shafts for
the transfer of rotational motion. These gears are manufactured
by special aluminum bronze material.
Clutch or friction pads:
An electric motor will get overloaded if it is connected directly to
the bowl assembly for the rotation of the same as the complete
assembly is very heavier. To avoid this, clutch or friction pads and
drum assembly are installed on the horizontal shaft.
As the motor starts, the pads inside the drum moves out gradually
due to centrifugal force and cause friction in the internal wall of
the drum resulting in rotation of the shaft and the bowl gradually
without overloading and damaging the motor and gears.

EJECTOR TYPE

NOZZLE TYPE

Bowl Top
Bowl
Bottom
Big Bowl
Ring
Bowl Top
Small
Ring
Top Disc
Distributer
Discs
Sliding bottom
Bowl

Vibration
A separator normally vibrates and produces a different sound when
passing through its critical speeds during run-up and run-down.
It also vibrates and sounds to some extent when running. It is good
practice to be acquainted with these normal conditions.
Excessive vibrations and noise indicate that something is wrong.
Stop the separator and identify the cause.
Use vibration analysis equipment to periodically check and record
the level of vibration.
The level of vibration of the separator should not exceed 9 mm/s.

Vibration switch (option)
The vibration switch, properly
adjusted, trips on a relative
increase in vibration.
The vibration switch is sensitive to
vibration in a direction
perpendicular to its base. It
contains a vibration detecting
mechanism that actuates a snap-
action switch when the selected
level of vibration is exceeded. After
the switch has tripped it must be
reset manually by pressing the
button on the switch.
RESET PUSH BUTTON
Sight glass
The sight glass shows the oil level in the oil sump.

Maintenance intervals
The following directions for periodic maintenance give a brief
description of which parts to clean, check and renew at different
maintenance intervals.
The service logs for each maintenance interval later in this chapter
give detailed enumeration of the checks that must be done.
Daily checks consist of simple check points to carry out for
detecting abnormal operating conditions.
Oil change interval is 1500 hours. If the total number of operating
hours is less than 1500 hours change oil at least once every year.

IS - Intermediate Service consists of an overhaul of the separator bowl,
inlet and outlet every 3 months or 2000 operating hours. Seals in bowl
and gaskets in the inlet/outlet device and operating device are renewed.
MS - Major Service consists of an overhaul of the complete separator
every 12 months or 8000 operating hours. An Intermediate Service is
performed, and the flat belt, friction elements, seals and bearings in the
bottom part are renewed.
3-year service consists of service of the coupling bearings, service of
frame intermediate part and renewal of frame feet. The rubber feet get
harder with increased use and age.

Daily checks

bowl partsNejat Öztezcan Chief Engineer 49

Dirt and lime deposits in the
sludge discharge mechanism can
cause discharge malfunction or
no discharge.
•Thoroughly clean and inspect
the parts. Pay special attention
to important surfaces (1, 2, 3
and 4). If necessary, polish with
steel wool.
•Clean nozzles (5) using soft
iron wire or similar. Note that
lime deposits can with
advantage be dissolved in a 10%
acetic acid solution.
Use Loctite 242 on the threads if
the nozzles have been removed
or replaced.

Check the sealing edge (a) of the
sliding bowl bottom.
If damaged through corrosion or
erosion or in other ways it can be
rectified by turning in a lathe.
Minimum permissible height of
sealing edge: 4,5 mm.

1
2
3
The bowl hood exerts a
pressure on the disc stack
clamping it in place.
Insufficient pressure in the disc
stack may affect the bowl
balance, which in turn will
cause abnormal vibration of
the separator and shorten the
life of ball bearings.
1. Place the bowl hood on the
top of the disc stack and
tighten it by hand.The
assembly mark on the bowl
hood should now be
positioned at the angle a 30° -
60° ahead of the corresponding
mark on the bowl body.
2. If the bowl hood can be
tightened by hand without
resistance until the marks are
in line with each other, an
extra disc must be added to the
top of the disc stack beneath
the top disc.

GENERAL OIL PURIFIER - (SLUDGE IS CLEANED MANUALLY)
(Conventional Type)
ALFA LAVAL MIB 303S-13/33
The motor is powered via an electronic frequency
converter which converts the incoming mains to
an output frequency of 125 Hz.
This gives the motor and bowl an operation
speed of 7500 rpm.
When the current is switched off the converter
acts as a brake and reduce the speed to below
1000 rpm. within 25 sec. Nejat Öztezcan Chief Engineer 54

OPERATION INSTRUCTIONS
If the amount of water and sludge in the oil is unknown, start the
seperator in CLARIFIER mode.
Run the separator 1-2 hours.
Then stop the separator and drain content from the outlet (C) into a
glass bottle. If water is found operate separator as a prufier.

STARTING :
PRUFIER MODE
After 20 sec. When the separator has gained full speed, feed at
least one litre of water into the inlet line. This will create the
water seal.
Turn on the oil feed to the seperator. Max. Recommended flow is
1000 litres/hour.
Check theat the oil has reached correct separating temperature.
Regulate the back pressure in the oil outlet line to 40 – 60 kPa.
Never run the unit longer than 3 days between bowl cleaning.

PA PURIFIER SYSTEM SYSTEM DESCRIPTION (ALFA LAVAL)
The PA Purifier System is designed for cleaning of;
• Marine diesel oil
• Intermediate fuel oil
• Heavy Fuel oil
• Lubricating oil
The system comprises:
• A separator
• Control Unit
• Oil feed pump, heater and sludge tank

OIL FLOW

Oil flow
The unprocessed oil is fed through a heater by a feed pump, operating at a
constant flow.
A change-over valve directs the oil to the separator. The cleaned oil is pumped
from the separator to either the daily service tank (fuel oil), or back to the
engine (lube oil).
During separator start and stop procedures and during alarm conditions the oil
is directed via a return line to the engine sump or settling tank.

SYSTEM LAYOUT
Clean oil outlet to
service tank

Definition of Terms
Preset time between sludge discharge sequences : When this time
has elapsed after a sludge discharge, the next discharge is initiated.
Water seal : Water, added to the separator bowl to prevent oil from
escaping at the water outlet.
Displacement water : Water, added to the separator bowl to displace
the oil and ensure there is reduced loss of oil at sludge discharge.
Purifier : A separator that cleans the oil from water and sludge
with continuous evacuating of separated water.

Prufier Process Cycle
1. A specific amount of water is added to the separator bowl to form a
water seal.
2. The feeding of unprocessed oil to the centre of the separator bowl
starts.
3. During the separation process sludge and water accumulate at the
periphery of the separator bowl. Cleaned oil is fed from the
separator by the integrated paring disc. Excessive water leaves the
bowl through the water/sludge outlet to the sludge tank.
4. After the preset time between discharge sequences, the oil feeding
stops.
5. Displacement water is added to the bowl. The displacement water
reduces the oil loss at the following sludge discharge.
6. A sludge discharge is initiated while the displacement water is still
flowing.
The next process cycle starts with adding of water for a new water
seal. Nejat Öztezcan Chief Engineer 68

OPERATION INSTRUCTION
Before Startup:
• Check that the separator is correctly assembled.
• Check the oil sump level.
• Chech the rotation of the bowl by doing a quick start/stop
Startup :
• Start the oil feed pump
• Switch ON the heater.
• Press the process Start/Stop button.
• Start the separator.
• When the separator is at full speed; START is shown on the panel.
• Wait until the oil feed temperature is correct.
• When the STANDBY is shown on the panel , press the process
start/stop button on the panel to start the separation.Nejat Öztezcan Chief Engineer 69

Start the oil feed pump
Switch ON the heater.
Press the process Start/Stop button.
Start the separator.
When the STANDBY is shown on the panel ,
press the process start/stop button on the
panel to start the separation.
PANEL

EMERGENCY STOP:
If an emergency situation occurs, press the emergency stop button and
evacuate the room.
Do not return until the separator has come to a complete standstill.

Design and function
The P type separator consists of three parts.
• lower part,
• the intermediate part
• top part with a frame hood.
The separator bowl (C) is driven by an electric
motor (A) via a flat-belt power transmission (D)
and bowl spindle (B).
The motor drive is equipped with a friction
coupling to prevent overload.
The bowl is of disc type and hydraulically operated
at sludge discharges.
The hollow bowl spindle (B) features an impeller
which pumps closing water from a built-in tank to
the operating system for sludge discharge.

Separating function
Liquid flow
Separation takes place in the separator
bowl to which unseparated oil is fed
through the inlet pipe (201). The oil is
led by the distributor (T) towards the
periphery of the bowl.
When the unseparated oil reaches the
slots of the distributor, it will rise
through the channels formed by the
disc stack (G) where it is evenly
distributed into the disc stack.
The oil is continuously separated from
water and sludge as it will flow towards
the center of the bowl. When the
cleaned oil leaves the disc stack it rises
upwards and enters the paring
chamber. From there it is pumped by
the paring disc (F) and leaves the bowl
through the outlet (220). Nejat Öztezcan Chief Engineer 74

Separated sludge and water
move towards the bowl
periphery.
In purification separated water
rises along the outside of the
disc stack, passes from the top
disc channels over the edge of
the gravity disc (K) and leaves
the bowl into the common
sludge and water outlet (221) of
the separator.
Heavier impurities are collected
in the sludge space (H) outside
the disc stack and are discharged
at intervals through the sludge
ports (L).

Water seal in purification
To prevent the oil from passing
the outer edge of the top disc (I)
and escaping through the water
outlet (221), a water seal must
be provided in the bowl.
This is done by filling the bowl
with water through the water
inlet (206), before unseparated
oil is supplied.
When oil feed is turned on the
oil will force the water towards
the bowl periphery and an
interface (X) is formed between
the water and the oil.
The position of the interface is
determined by the size of gravity
disc (K). Nejat Öztezcan Chief Engineer 76

Displacement of oil
To avoid oil losses at sludge
discharge, displacement water
is fed to the bowl.
Prior to a discharge the oil feed is
stopped and displacement water
added through the water inlet (206).
This water changes the balance in
the bowl and the interface (X)
moves inwards to a new position
(Y), increasing the water volume in
the sludge space.
When the sludge discharge takes
place sludge and water alone are
discharged.
A new water seal will be
established immediately
afterwards. The oil feed is then
turned on again. Nejat Öztezcan Chief Engineer 77

Gravity disc
In the purification mode, the position of the interface (X) can be adjusted by
replacing the gravity disc (K) for one of a larger or smaller size.
A gravity disc of a larger size will move the interface towards the bowl periphery,
whereas a disc of a smaller size will place it closer to the bowl centre.
The correct gravity disc is selected from a nomogram.

Clarifier disc
In the clarification mode, the gravity disc is replaced by a clarifier
disc which seals off the water outlet.
In this case no water seal is required and consequently there is no
oil/water interface in the bowl.
The clarifier disc is an optional disc with a hole diameter of 40 mm.

Sludge discharge function
Sludge is discharged through a number of
ports (L) in the bowl wall.
Between discharges these ports are covered
by the sliding bowl bottom (M), which forms
an internal bottom in the separating space of
the bowl.
The sliding bowl bottom is pressed upwards
against a sealing ring (m) by force of the
closing water underneath.
The sliding bowl bottom is operated
hydraulically by means of operating water
supplied to the discharge mechanism from
an external freshwater line.

Opening water is supplied directly to the
operating system in the bowl while
closing water is supplied to the built- in
closing water tank, and pumped to the
operating system through the bowl
spindle.
The opening and closing only takes a
fraction of a second, therefore the
discharge volume is limited to a certain
percentage of the bowl volume. This
action is achieved by the closing water
filling space above the upper distributor
ring and pushing the sliding bowl bottom
upwards. Simultaneously, the water in
the chamber below the operating slide is
drained off through the nozzles in the
bowl body. Nejat Öztezcan Chief Engineer 82

Bowl opening
The key event to start a sludge
discharge is the downward movement
of the operating slide. This is
accomplished by supply of opening
water (372) to the discharge
mechanism. Water is drained off
through nozzles (Y) in the bowl body.
The sliding bowl bottom is rapidly
pressed downwards by the force from
the liquid in the bowl, opening the
sludge ports.
Bowl closing
After the sludge is discharged the
sliding bowl bottom is immediately
pressed up and the sludge ports in
the bowl wall are closed.

•Three different water are given to the separator.
•DISPLACEMENT WATER : Low Pressure Operating water (Cold
Water) 0,1/0,25 Bar.
•OPENING WATER : (Cold water ) (Shock Water) 1,5/3 Bar
•CLOSING WATER : 2/4 Bar (Cold or Warm Water).

Bowl spindle
In addition to its primary role in the
power transmission system, the bowl
spindle also serves as:
•pump for the closing water
•supply pipe for the closing water
•lubricator for spindle ball bearings.
Closing water is pumped through the
hollow spindle (B) to the discharge
mechanism in the bowl. For this
purpose a pump sleeve (b4) is fitted in
the lower end.

Purifying operation process a
centrifugal force acting on the pilot
valve seals the valve seat and the
water pressure chamber for closing
bowl is filled with operating water.
The operating water pressure pushes
up the main cylinder to seal the main
seal ring for purifying operation.
Operating water for closing bowl is
intermittently introduced into the
bowl closing water pressure chamber
for a given period of time during
purifier operation. In the water
pressure chamber, the centrifugally
generated pressure of water that
turns with the bowl is balanced with
the supplied water pressure told the
water surface at a certain level.Nejat Öztezcan Chief Engineer 87

Opening bowl process
Operating water for opening bowl is
fed for a certain time to the water
pressure chamber for opening bowl.
It partly goes out through the drain
nozzle. More operating water for
opening bowl is supplied and fills up
the water pressure chamber for
opening bowl.
As its pressure slides the pilot valve
toward the shaft center, the seal of
valve seat breaks and operating water
for closing bowl flows out from the
bowl. Nejat Öztezcan Chief Engineer 88

Sludge discharging process
When operating water for closing bowl goes
out, there is no more force of pushing up the
main cylinder that, then, is pushed down by
the pressure in the bowl. The seal of main
seal ring breaks and sludge is instantly
discharged outside the bowl.
Closing bowl process
After the sludge discharge,
operating water for closing
bowl is fed to the water
pressure chamber for closing
bowl and, when it is filled
up, the main cylinder is
pushed up to seal the main
seal ring.

Control panel
The control panel repeatedly and automatically performs SELFJECTOR
operating steps shown in below:

Multi- Monitor (MM) :
The Multi-Monitor forms an integrated detection system with a
Leakage Monitor, a Discharge Detector and a Water Detector.
It has displays to indicate the operational status data of SJ-G series
SELFJECTOR such as flow rate, temperature, pressure and speed.
This instrument contains a serial board (RS485) that enables
communication with the control panel.

Leakage Monitor Function (LM)
The Leakage Monitor detects a leakage of treated oil from the
bowl's sludge outlet or heavy liquid output by means of a pressure
sensor and delivers an alarm signal to the automatic control panel
via the Multi-Monitor.
The pressure sensor is located on the light liquid outlet-side bracket
of the SELFJECTOR and normally maintained under a certain level of
pressure by means of a pressure control valve.
When a leakage occurs, an ensuing pressure drop is detected by the
pressure sensor and an alarm signal is sent to the automatic control
panel.

Discharge Detector Function (DD)
The Discharge Detector monitors the horizontal shaft speed by means
of a proximity sensor and determines whether or not sludge discharge
has properly taken place by means of an input data comparison
circuit.
When abnormal discharge is detected, an alarm signal is issued to the
automatic control panel via the Multi-Monitor. In addition to this
alarm output function, the Discharge Detector of the partial discharge
type purifier has a display function to tell whether or not the sludge
discharge is optimal for partial discharge adjustment.

Water Detector Function (WD)
The Water Detector is available in a pressure type and an electrostatic
capacity type.
The pressure type is designed to monitor the level of water
accumulated in the bowl by means of a pressure sensor provided in
the circulation line that returns some of purified oil to the feed liquid
inlet.
The electrostatic capacity type, which is installed in the purified oil
piping of the purifier, is designed to work on the principle that
capacitance (dielectric constant) rises as oil increases in water content.
When the water content of purified oil exceeds an alarm trigger level,
the Water Detector issues an output signal to the automatic control
panel for sludge discharge via the Multi-Monitor.

STRUCTURE of SELFJECTOR
The power is transmitted from
the motor through the friction
clutch to the horizontal shaft
and is further increased in speed
and transmitted to the vertical
shaft through the spiral gear
mounted on the horizontal shaft
and pinion on the vertical shaft.
The vertical shaft is supported
by upper and lower Motor
bearings. The bowl mounted on
the top of the vertical shaft
rotates at the speed of the
vertical shaft.

Horizontal shaft section
Between the motor and horizontal
shaft, the friction clutch is provided.
The horizontal shaft is supported by 2
ball bearings built in the bearing
housing (3) and bearing housing (4).
Between them, the spiral gear is
mounted. The bearing housings (3)
and (4) are provided with oil seals to
avoid gear oil leakage.
The horizontal shaft is directly
coupled with the gear pump by the
safety joint.
~

Brake
By springs, the brake linings are
pressed against the outer surface
of friction pulley to perform
braking.
Use the brake only when quick
stop is absolutely required in
emergency, for repair or checkup.
For normal stoppage and not in
emergency, refrain from braking
and allow the rotation to stop
coasting.

Friction clutch
A friction clutch is used for gentle
starting and acceleration, thereby
preventing the motor from being
overloaded.
The motor shaft has a friction boss
provided with a friction clutch and the
horizontal shaft has a friction pulley.
After starting, the motor instantly
turns at critical speed, the friction
clutch lining is pressed against the
internal surface of the friction pulley
via centrifugal force and the power is
transmitted to the friction pulley
(horizontal shaft side) as the friction
pulley and lining slip with each other.Nejat Öztezcan Chief Engineer 98

Typical alarms and shut downs
The following gives a general list of alarms only some of which may be
fitted.
•Back Pressure shutdown- this measures the discharge oil pressure and
alarms and initiates a shut down when below a set value.
•Heavy phase overflow. Oil has a much higher viscosity than water. The
heavy phase outlet is led to a small catchment tank containing a float.
The outlet from the tank is restricted in such a way that water flows
freely but oil tends to back up. This initiates an alarm and shut down.

•Bowl not open- This may be dome in several ways, typically by a
lever switch operated by the discharged sludge hitting a striker plate.
Another method is by measuring the motor current, when
the bowl opens the bowl speed is dragged down due to friction
effects of the discharging sludge and water. The motor current rises
until full speed is reestablished. This is detected by a current sensing
relay
•Water in oil- This found on modern designs which have a detection
probe mounted in the oil discharge
•High temperature alarm and shut down
•Low control/seal water pressure. Where control water is supplied
via a fixed small header tanks a float switch may be fitted.

•Back Pressure: The back pressure should be adjusted after the
purifier is started. ( approx.1,5 Bar for F.O and 1 Bar for Lub.Oil)
The back pressure varies as the temperature, density, viscosity of
feed oil inlet varies.
The back pressure ensures that the oil paring disc is immersed in
the clean oil on the way of pumping to the clean oil tank.
• Throughput of oil feed: Throughput means the quantity of oil
pumped into the purifier/hr.
In order to optimize the purification, the throughput must be
minimum.

• Feed inlet oil temperature: Before entering the purifier, the dirty
oil passes through the heater.
This increases the temperature, thus reducing the viscosity of the
oil to be purified.
The lower the viscosity, the better will be the purification.
•Density of Oil: As the dirty oil entering the purifier is heated to
reduce the viscosity, the density also reduces.
The lower the density, the better the separation.
•R.P.M of the rotating bowl: If the purifier has not achieved full RPM
(revolutions per second), then the centrifugal force will not be sufficient
enough to aid the separation.

Cleaning-in-Place (CIP) :
When fouling occurs, an Alfa Laval CIP system enables quick and
easy in-line cleaning of heat exchangers and high-speed separators
without dismantling your equipment.
•Reduced operating costs
•Quick, effective cleaning

What is gravity disc ?
The gravity disc is important part of purifier, which set the location of
the oil, and water interface line, which is variable according to the
maker’s design.
How to choose the correct size of gravity disc ?
Correct size is selected using:
•Separation temperature
•Density of oil at this temperature
•Desired throughput of oil and by using of nomogram from the
purifier manual.
What is paring disc ?
It is a stationary impeller mounted in a chamber at the neck of the
bow.
Its function is to convert the rotating energy of the liquid into a
pressure head. Nejat Öztezcan Chief Engineer 107

Compare purifier and clarifier ?
Purifier
Remove water and suspended solids particles from oils
Two outlets water and clean oil
Gravity disc on top
Blind disc on the top of disc stack
Sealing water required
Clarifier
Remove finer and lighter particles from oil
One outlet for clean oil
No gravity disc only sealing ring
Blind disc at bottom.
Sealing water not required

How do you change purifier to clarifier ?
Open up the purifier and set the blind disc at the bottom of the disc stack.
The water outlet is blocked by a seal on the gravity disc.
Blank off the sealing water inlet line.
What is purifier, clarifier ?
Purifier is a centrifuge, which is arranged to separate water and solid impurities
from oil.
Clarifier is a centrifuge, which is arranged to separate finer solid impurities from
the oil.
How to change purifier from HFO to DO ?
Replace the gravity disc, which is smaller than the heavy oil
Open heater by pass vale.
Close the FO heater steam in/out valves.
Open heater drains v/v.
Pure DO purifier cannot change to HFO, it has no heater.
Pure clarifier cannot change to purifier, it has no water outlet.

Why multidisc provided inside purifier ?
To separate the liquid into thin layer & create shallow settling distance
between discs.
Improving separation of oil from heavier liquids & solids particle
Cause of excessive vibration on purifier ?
•Sludge too much inside the bowl
•Foundation damper & spring failure
•Bearing failure
•Worn gear
•Uneven wear of frictional clutch
•Motor speed too high or too low
Why need sealing water ?
To seal the water outlet & to prevent the overflow of oil from the water
outlet.

What are reaseons for purifier over flow ?
•Incorrect purifier disc size (inside diameter too large)
•Too low fuel oil temperature
•Too much rate of throughput
•Too much sludge inside the bowl
•Low speed (rpm) of bowl rotation
•Sealing water failure
•Operating water failure
•Worn out main sealing ring
Why purifier is not building up speed while running ?
•Improper touching with friction clutch (worn out frictional clutch)
•Touching with break
•Excessive sludge in the bowl
•Bearing failure
•Motor running at overload
•One phase power failure (Single phasing)
•Sump oil level too high
•Vertical shaft and horizontal shaft are out of alignmentNejat Öztezcan Chief Engineer 111

How is the capacity of separator decided for a ship?
•20% more than the consumption of the ship for heavy oil and 3
times the daily consumption of lube oil.
•What are the types of oil separators present on board a
vessel?
•Clarifier and purifier.
What is the purpose of gravity disc?
It determines interface between high and low density medium and
maintains it. To control water flow through water port outlet
(Size of the gravity disc is selected according to specific gravity of
oil).

Which factor determines the size of the gravity disc for a fuel oil
centrifugal purifier?
a) The viscosity of the fuel.
b) The quantity of water to be removed from the fuel.
c) The specific gravity of the fuel.
d) The quantity of dirt to be removed from the fuel.
While operating the fuel oil centrifuge prufier, the fuel oil is being
continuously ejected with the sludge.
a) gravity disk inside diameter is too large
b) gravity disk inside diameter is too small
c) back pressure is too low
d) incorrect number of disks have been place

While operating the fuel oil prufier, the bowl fails to open for sludge
ejection. The probable cause is that __________.
a) one or more of the sludge ports is partially clogged
b) the operating water pressure is too high
c) the bowl disk set is clogged
d) the seal ring on the operating slide is defective
During the operation of the fuel oil centrifuge, it is found that the
'clean' oil discharge contains water. The most probable cause is the
__________.
a) gravity disk is too large
b) throughput is too high
c) separating temperature is low
d) clean oil outlet valve has not been fully opened

Which of the following conditions would cause the ‘prufier low
pressure in oil outlet' alarm to be illuminated?
a) Throughput too low.
b) Separating temperature too high.
c) Line to pressure switch obstructed.
d) All of the above are correct.
The most effective method in removing water from diesel fuel oil is
by __________.
a) centrifuging the fuel
b) using it in the engine
c) heating the fuel tanks
d) straining the fuel

On board supply vessels, a centrifuge is normally used to purify
__________.
a) cooling water
b) fuel oil
c) sea water
d) diesel intake air
Heavy residual fuel oils are heated prior to centrifuging to
__________.
a) reduce fuel weight
b) increase specific gravity
c) separate fuel from lube oil
d) reduce fuel viscosity

When preparing to clean the fuel oil prufier, the bowl must be
brought to a complete stop to avoid ________ .
a) contamination of the clean fuel oil
b) irreparable damage to the unit
c) contamination of the unit's lube oil supply
d) premature loss of the bowl seal liquid
A centrifugal oil prufier should be shut down if the;
a) Presence of oil indicated in the gravity tank
b) Observation cover clamps needs tightening
c) Prufier is vibrating badly
d) Trapped water is discharced from the overflow line

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