Alpha Laval Filters

Automatic filters for mineral oil

Technical information for oil filtration

Inside view

3 Summary

4 Background

5 Filtration theory

8 The Alfa Laval filterDesign, automatic filter with diversion chamberFeatures of the Alfa Laval automatic mineral oil filterOperating principle, automatic filter with diversion

12 New filter rangeDesign, automatic filter with integrated centrifugeFeatures of the Alfa Laval “Eliminator” automatic mineral oil filterOperating principle, automatic filter with integrated centrifuge

16 Lubricating oil filtrationGeneralDesignation and operation conditions for Alfa Laval lubricating oil filtersAlfa Laval lubricating oil filters for crosshead enginesPre-lubricationDimensioning criteria for Alfa Laval lubricating oil filters

19 Fuel oil filtrationGeneralDesignation and operation conditions for Alfa Laval fuel oil filtersDimensioning criteria for Alfa Laval fuel oil filters

This technical information deals with filtration technology in generaland the Alfa Laval automatic filters in particular.

Alfa Laval Automatic Filters

2 Alfa Laval Marine & Diesel Equipment

Alfa Laval Marine & Diesel Equipment 3


SummaryAutomatic filters from Alfa Laval offer continuous engine protection. The filterseffectively use clean oil as the flushing medium to prevent any particles present in lubricating oil or fuel oil from causing injector and engine damage.

Alfa Laval offers a range of automatic filters that provide full-flow filtering of fuel and lubricating oils for trunk piston andcrosshead engines. Used in conjunction with a centrifugalseparator as part of a complete lubricating oil system or fueloil treatment system, these filters effectively separate impuri-ties, according to size. Configuration is flexible, depending onthe application.

Continuous backflushing helps prevent adhesion of retainedsolids to filter surfaces. This ensures long service intervalsand drastically reduces the costs for manual cleaning, filterreplacement and filter disposal. The robust disc-type filter elements operate at a low and constant pressure drop, pro-viding high filtering efficiency and reducing the risk of cracking.

These four different filter types are available:

• automatic filter for lubricating oil,

• automatic filter for lubricating oil with diversion chamber,

• automatic filter for lubricating oil with integrated centrifuge,and,

• automatic filter for fuel oil.

The Alfa Laval filters have been installed on virtually all typesand brands of diesel engines.

The purpose of this document is to provide technical informationabout Alfa Laval automatic filters. This includes informationabout the filtration process, filter design and dimensioning,working principles and operating conditions.

Benefits• Easy to install and operate. These compact, lightweight

automatic filters require very little floor space. Hydraulicallydriven by the pressure of the backflushing oil, the filters donot require external power supply, compressed air orelectricity for operation.

• Flexible design. These filters are easily installed in varyingpipework configurations. Alternatives to the standard con-figuration of these automatic filters are available to meet thespecific requirements of the engine manufacturer.

• High filtration efficiency. Robust disc-type filter elementsefficiently separate impurities according to size from the oil.These elements operate at a low and constant pressuredrop, thus reducing the risk of cracking.

• Reduced maintenance costs. Continuous backflushinghelps prevent adhesion of retained solids to filter surfaces.This ensures longer service intervals – up to 12,000 hours –and drastically reduces the costs of manual cleaning, filterreplacement and filter disposal.

Lubricating oil filter Lubricating oil filterwith diversion chamber

Lubricating oil filter with integrated centrifuge

Fuel oil filter



BackgroundThe filter, in a mineral oil treatment system for diesel engines, is installed primarilyfor preventing particles in the oil from entering the engine. Hence, the filter shouldbe placed as close to the engine as possible, whether it is operating as a fuel oilor lubricating oil filter.

The centrifugal separator, on the other hand, cleans the oiland removes the water. For these reasons, both theseparator and the filter are required in a modern mineral oilcleaning system.

The main difference between a filter and a centrifugal sepa-rator is that a filter separates the impurities according to size,while a separator works with the density difference betweenthe impurities and the oil.

Automatic full-flow filter for lubricating oil.Automatic full-flow filter for fuel oil.

Filtration theoryFiltration can be defined as the process of collecting solid particles from a fluid bypassing the fluid through a filter medium (which could be a filter screen or a paperelement) where the particles are retained.

Two basic methods of filtration are used:

1. surface filtration, used in strainers and cake filters, and,

2. deep-bed filtration, used in depth filters.

The principles of particle collection in surface filtration anddeep-bed filtration are entirely different.

In surface filtration the particles are collected on the surfaceof the filter medium, whereby a filter cake of retainedparticles is created. This cake can be removed bybackflushing the filter.

In deep-bed filtration the particles pass through a filter andare collected inside the filter. Since different capturemechanisms are used in surface filtration and deep-bedfiltration, the value of comparing filter finenesses of the twotypes is questionable.

Figure 2 shows the different mechanisms operating insurface filtration and deep-bed filtration, respectively.

As the solid particles accumulate in a depth filter, thepressure drop increases during filtration. When the pressuredrop reaches a certain level, the filter elements must bereplaced.

Figure 3 shows examples of filter screen configurations usedon surface filters.



Fluid with solid particles

Filtrated fluid (Filtrate)

Filter medium

Figure 1. Schematic diagram of a filtration system.

Fluid

Cake of captured particlesFilter medium Filter medium

Deep-bed filtrationSurface filtration

Fluid

Figure 2. Principles of surface and deep-bed filtration.

Figure 3. Examples of filter cloths.

A B C D E F

Due to the different screen configurations, comparisons ofgiven filter finenesses on different filter screens with oneanother are of doubtful value.

The advantage of using a surface filter, rather than a depthfilter, is that the filter screens can be cleaned, thus the filter can be reused. If the filter is backflushed continuously, thepressure drop across the filter will remain constant.

In practice, a filter can be retained in operation withoutinterruption, provided that the backflushing is a part of thefilter construction. If so, the filter is called automaticbackflushing, or just automatic.

How efficiently a surface filter will remove solid particles is acomplex question, because the particles do not have aregular spherical shape. Particles of different sizes and

shapes could therefore pass through, or be stopped by, thesame square opening, depending on how they enter the filterscreen. Figure 4 shows some different particle shapes.

If all the particles had a regular spherical shape, the removalefficiency rate in a filter screen with a square opening of35 µm would be as shown in Figure 5.

All particles larger than the square opening would beremoved and all particles smaller than the square openingwould pass through.

However, as the particles are not spherical, the question ofwhether a certain particle may or may not pass through thefilter screen openings will depend on how the particleapproaches the screen. In practice, particle removal is asshown in Figure 6.



Figure 4. Examples of particle shapes.

%Removaleff.

100

75

50

25

10 20 50 60 µm

0

0 35

%Removaleff.

100

75

50

25

10 20 50 60 µm

0

0 35

Figure 5. Example of removal efficiency for spherical particles. Figure 6. Example of removal efficiency for irregularly shaped particles.

Consequently, some particles larger than the square openingwill pass through, and some particles smaller than the squareopening will not.

When comparing surface filters, it is important to specify thesize of the square opening being used. Since particles haveirregular shapes, their ability to pass or not pass through thefilter depends on whether they arrive at the filter screen withtheir small end first, or broadside. The term “nominal filterfineness” has therefore been applied to surface filters.

The term for “absolute filter fineness” (often called “absolutemesh size”) refers to the square opening, as shown in Figure 7.

In the marine and power industries, the following example isoften cited to clarify the relationship between nominal andabsolute fineness in a surface filter, measuring for example20 µm nominal filter fineness: 85–90% of all particles largerthan 20 µm are retained in a surface filter with a filter finenessof 35 µm absolute.

When the same relationship is applied to other filterfinenesses, the following figures are obtained:

• 10 µm nominal → 25 µm absolute






However, this does not apply to depth filters. Normally,particles smaller than the given filter fineness are removedmore efficiently in a depth filter compared to a surface filterwith the same given filter fineness. Therefore, depth filtersmight become clogged by these small and harmlessparticles, which need not be removed.

Due to difficulties in manufacturing a depth filter with equalsized pores, it may be less effective for large particles than asurface filter.

An empirical relationship valid for surface filtration betweenfiltrate flow (Q), filtrate viscosity (ν), filter area (A) and thickness

(δ) and differential pressure across the filter (∆p) is found to be

Q = K xA x ∆p

(1)υ x δ

(K = a constant depending on the permeability of the bed)

The formula describing this relationship, Darcy’s basicfiltration equation, is named after the man who formulated it.

This formula is valid when the differential pressure through thefilter cake is low and the main pressure drop occurs acrossthe filter medium itself, i.e., when the filter medium is fairlyclean. In these circumstances, the filtrate flow through eachsquare opening in the filter medium is low, and the flow issaid to be laminar.

If the suspension medium is an absolutely clean liquid, thecumulative filtrate volume will increase linearly with time, inaccordance with Darcy’s equation. In practice this holds trueat the beginning of the filtration period, but as time passes,the cumulative filtrate volume tapers off. This is shown inFigure 8.

When a filter cake begins building up, the simple relationshipexpressed by Darcy’s equation is no longer valid, because theresistance through the filter (K/δ in Darcy’s equation) is nolonger constant. The resistance increases as filtration timeincreases, and can be written as:

Total resistance = K/δ (constant) + Rc

(increasing with time),where R

c= resistance through filter cake.

When the filter cake is compressed, the relationship becomeseven more complex.

In this case the resistance through the filter is also a functionof the differential pressure through the filter, i.e., both thedifferential pressure and the filter resistance increase duringfiltration.



Absolute filter fineness

Time, t

Cumulative filtratevolume, V

Clean liquid

Suspension

Figure 8. Cumulative filtrate volume as a function of time.

Figure 7. Definition of “absolute filter fineness”.



Unfilteredoil

Filtered oilto engine

Filteredoil

Unfilteredoil

Filteredoil

To lubricatingoil sump

Hydraulic motor

Drain cock

Filteredoil to hydraulicmotor

Distributor

Strainer

Full-flowchamber

Diversionchamber

Figure 9. Automatic lubricating oil filter with diversion chamber.



DesignThe Alfa Laval filter consists of: • the filter housing,• the filtering unit and distributor, and, • the hydraulic motor.

The filter housing for the automatic filter can have one or twochambers. The first chamber, where the cleaning of the oiloccurs, is called the full-flow chamber. The second chamber,where the impurities stopped by the full-flow chamber arecollected, is called the diversion chamber. Cross-sections ofthe filter with diversion chamber are shown in Figure 9.

The filter unit contains disc-type filter elements placed on topof one another forming a very robust filter disc stack. Theconstruction is designed in such a way that the filter elementsare pressed together not only by rods, but also by the oilpressure on the end cover at the bottom of the filter stack.Full-flow and diversion elements are shown in Figure 10.

This construction efficiently prevents leakage of oil betweenthe filter elements because the elements are pressed morefirmly together as the pressure drop over the filter increases.A part of a filter disc stack is shown in Figure 11.

The elements are divided into sections by ribs. Together theyform independent filtering columns. The number of filterelements in the filter disc stack, the diameter of the discs andthe fineness of the filter screen are factors that determine thecapacity of the filter.

The capacity of the Alfa Laval filter system can be furtherincreased by using a special arrangement of two or three filterunits in parallel.

The filter disc stack, together with sleeve, covers, rods, etc.,forms a “filtering unit”, in which the “distributor” for the auto-matic filter is located. The distributor, driven by the hydraulicmotor, in a step-wise manner feeding unfiltered oil to allcolumns except one that is open for backflushing. In this way, each column is backflushed once per rotation of thedistributor (continuous backflushing).

The filter is backflushed approximately once every secondminute, but as the backflushing is always made on at leastone sector, the backflushing flow is continuous.

A filtering unit is shown in Figure 12.

The Alfa Laval filterDesign and operating principle

The Alfa Laval automatic filters are designed specifically for full-flow filtering of fueland lubricating oils for trunk piston and crosshead engines.

Full-flow filtering elementDiversion filtering element

Figure 12. Filtering unit.

Figure 11. Alfa Laval disc-type filter elements.

Figure 10. Filtering elements.

Filter frame

Distributor

Full-flow elements

Diversion elements

Cover

Sleeve

Rod

Filter cloth

Rib

The filtering unit and distributor are placed in the filterhousing, which, for the automatic filters with filtration of thebackflushing oil, forms two filter chambers:

• the full-flow chamber with full-flow filter elements, where the harmful solids are removed from the oil flowing towardsthe engine

• the diversion chamber with diversion filter elements, where the backflushed oil is filtered and the solids will beconcentrated and removed from the oil system by periodicdraining.

The distributor is rotated by the hydraulic motor, which in turn is driven by a small supply of the oil from the outlet of the filter (approximately 200 l/h).

The hydraulic motor is located on top of the filter housing.(See Figure 13, which also shows the filter inlets and outlets.)

Features of the Alfa Laval automatic mineral oil filter• Constant pressure drop during operation due to continuous

backflushing.

• Filter screen is kept clear by continuous backflushing,which means that long service intervals can be achieved,without accumulation of particles on filter screen.

• Robust disc-type filter elements.

• Simple installation and operation, without electricity orcompressed air.

• Compact, lightweight design.



Figure 13. Automatic filter for lubricating oil, with diversion chamber.

Return

Drainvalve

Pressure dropindicator

Outlet

Inlet

Hydraulic motor

Diversionchamber

Full-flowchamber

Operating principle, automatic filter with diversion chamberThe operating principle of an automatic filter is explainedbelow. (The capital letters in the text refer to Figure 14.)

Phase 1Filtering in the full-flow chamber1. Unfiltered oil enters the full-flow chamber of the filter at “A”

and flows into chamber “B” – the space between thedistributor “C” and the inner perimeter of the sleeve wherethe filter elements “D” are fitted.

2. From chamber “B” the oil is distributed into and throughthe filtering columns formed by elements “D”. The solidspresent are trapped.

3. The filtered oil is fed into chamber “E”, where it flows to theengine through the filter outlet “F”. Approximately 200 l/h of the filtered oil flows from chamber “E” to the hydraulicmotor “H” through the feed pipe “G” to drive the hydraulicmotor.

Backflushing in the full-flow chamber4. While the “full-flow” filtration takes place in all columns

except one, solids are removed in one column by back-flushing, using part of the filtered oil from chamber “E”.

5. The backflushing oil with its solids passes through channel“K” in the distributor “C” to the diversion chamber “L”.

Filtering in the diversion chamber6. The backflushing oil passes from diversion chamber “L”

through the diversion filter elements “M” to the passage inthe distributor “N”.

7. Filtered oil is taken back through passage “N” in thedistributor via outlet “P”.

8. In this first phase, no backflushing is performed in thediversion chamber.

Phase 2Filtering in the full-flow chamber and diversion chamberBackflushing in the diversion chamberIn this phase, the distributor has rotated one step comparedwith Phase 1.

9. Part of the filtered oil in chamber “E” can now passthrough the channel “R” in the distributor and through thediversion filter elements “M” (from inside to outside)removing the trapped particles from the outer side of theelements.

10. The particles trapped by the filtering elements “M” canthus settle to the bottom of the diversion chamber “L”.

Removal of the filtered solids11. The solids filtered out in the diversion chamber are then

discharged from the system by periodic draining by anautomatic or manual valve “V”.



Figure 14. The flow of oil through an Alfa Laval filter.

N

P

L

K

E F

C

B

A

H

M

G

D

Phase 1

Phase 2

M

L

V

N

P

R

E F

A



DesignThe Alfa Laval “Eliminator” filter consists of:• the filter housing,• the filtering unit and distributor,• the hydraulic motor, and,• the centrifuge.

The first chamber, where the harmful particles are stoppedbefore they can find their way to the engine, is called the full-flow chamber. The particles trapped in the full-flow chamberare driven to the solid bowl centrifuge by backflushing, whereall the particles, even the smallest ones, are trapped on thecentrifuge wall. Clean oil is driven back from the centrifuge tothe oil sump. The centrifuge is driven by the circuit oilpressure. Cross-section of the filter is shown in Figure 15.

The filtering unit contains disc-type filter elements. Assembledtogether they form a robust disc stack. The filtering elementsare divided into sections by ribs. When assembled together,they form independent filtering columns.

The filter disc stack, together with filter head, sleeve,distributor, rods and covers, forms the filtering unit. Thedistributor, driven by the hydraulic motor, rotates at regular

New filter rangeAutomatic filter with integrated centrifuge

Figure 15. Automatic lubricating oil filter with centrifuge.

Figure 17. Flow distribution through the full-flow filtering element.

Distributor

Backflushed oil(to the centrifuge) Clean oil to

the engine

Unfiltered oil

Figure 16. Full-flow filtering element.

Hydraulic motor

Distributor

CentrifugeFiltered oil to the engine

Full-flow chamber Centrifuge chamber

Unfiltered oil

Filtering unit

Cleaned oil back to oil sump

intervals, feeding unfiltered oil to all columns except one, thatis open for backflushing. In this way, each column is back-flushed once per full rotation of the distributor (continuousbackflushing). A filtering unit is shown in Figure 18.

The distributor is rotated by the hydraulic motor, which isdriven by a small amount of the clean oil downstream thefilter elements. The hydraulic motor is located on the side ofthe filter housing (see Figure 20).

The backflushed oil from the full-flow chamber enters thecentrifuge, where a high efficiency axial disc stack separatesthe harmful particles from the oil. The particles collect on therotor wall. The cleaned oil is ejected through the nozzles,which give the rotating energy for the centrifuge, then the oilgoes back to the lubricating oil sump by gravity. (See Figure 19.)

Features of the Alfa Laval “Eliminator” automatic mineraloil filter• Constant pressure drop during operation due to continuous

backflushing.

• Contamination level of the oil kept at very low level, thanksto the high efficiency disc-stack centrifuge.

• Filter screen kept clear by continuous backflushing whichmeans that long service intervals can be achieved.

• Robust disc-type filter elements.

• Simple installation and operation, without electricity andcompressed air.

• Compact, lightweight design.

Unfiltered oilFiltered oilto the engine

Hydraulic motor

Cleaned oilback to oil sump

Full-flow chamber Centrifuge chamber



Figure 20. “Eliminator” Automatic Filter with centrifuge.

Figure 18. Filtering unit.

Completefiltering unit

Filtering element

Filter head

Distributor

Rod

Sleeve

Figure 19. Centrifuge chamber.

Backflushed oilfrom full-flow

filter

Rotor wall

Axial disc stack

Nozzles

To lubricating oil sump

Operating principle, automatic filterFiltering in the full-flow chamber1. Unfiltered oil enters the filter at “A” and flows through the

strainer “S” into the chamber “B” – the space between thedistributor “C” and the inner perimeter of the sleeve “J” onwhich the full-flow filter elements “D” are mounted.

2. The oil is distributed from this space through the full-flowfilter elements “D” in eleven of the twelve filtering columns(the twelfth column is being backflushed). The solids aretrapped on the inner side of the elements in the elevenfiltering columns.

3. The filtered oil flows into the full-flow chamber “E” and isfed through the filter outlet “F” to the engine.

4. A few hundred litres per hour of the filtered oil are routedfrom the full-flow chamber “E” to the hydraulic motor “H”to drive the distributor “C”.

Backflushing in the full-flow chamber1. While the full-flow takes place in eleven columns, solids

are being removed from the elements in the twelfth columnby backflushing (from outside to inside of the column)using part of the filtered oil from the full-flow chamber “E”.

2. The backflushed oil with removed solids flow through thepassage “K” in the distributor “C” and is routed to thecentrifuge “W”, where the solids will be removed from theoil before it goes back to the sump.



Figure 21. “Eliminator Automatic Filter with centrifuge.

H E F A S

B

J

W

D C

Operating principle, centrifugeIntroductionThe purpose of separation is to separate solid particles froma liquid.

Separation by gravityA liquid mixture in a stationary bowl will clear slowly as theheavy particles in the liquid mixture sink to the bottom underthe influence of gravity. A liquid rises, while solids sink.

Continuous separation and sedimentation can be achieved ina settling tank that has outlets arranged according to thedifference in density. Heavier particles in the liquid mixture willsettle and form a sediment layer on the tank bottom.

Centrifugal separationIn a rapidly rotating bowl, the force of gravity is replaced bycentrifugal force, which can be thousands of times greater.

Separation and sedimentation are continuous and occurquickly.

The centrifugal force in the separator bowl can achieve in afew seconds what takes many hours in a tank underinfluence of gravity.

Power transmissionThe energy necessary to rotate the bowl is taken from the oilpressure, which rotates the bowl using the force of thereaction created when the oil passes through the calibratednozzles.



Figure 22. Operating principle.

Figure 23. Separation by gravity.

Figure 24. Centrifugal separation.

Dirty oil

Clean oil

Clean oilDirty oilNozzle



GeneralThe complete lubricating oil system of a diesel engineincorporates a full-flow oil circuit (the main lubricating oilsystem) and, for almost all engines operating on residual orheavy fuel oils, a bypass lubricating oil circuit (the cleaningsystem). The oil flow in the cleaning system is approximatelyone percent of the oil flow in the main lubricating oil system.The full-flow circuit contains a lubricating oil filter system (see Figure 25).

The role of the filter system is to protect the engine fromharmful particles. The entire lubricating oil flow to the enginepasses through the filter system, where the harmful particlesare stopped.

The role of the bypass circuit is to remove harmful conta-minants (solid particles and water) from the lubricating oilsystem in order to keep the contamination concentration atan acceptable level. This is done by means of the centrifugalseparator.

The filter system contains one main filter, or, if the lubricatingoil flow is high, two or several main filters in parallel. Oftenthere also is a bypass filter in parallel with the main filter,which is used if the main filter is stopped.

An indicator or security filter is often installed. Its function is tostop particles from entering the engine in case of malfunctionof the main filter. This filter (or filters if the oil flow is high) alsoindicates if something is wrong with the main filter.

The filter system can be built by using one of the followingthree systems:

• Two parallel identical manual filters(one in use, one on stand-by).Common on smaller enginesoperating on diesel or marinediesel oil.

• One automatic backflushing filteras main filter plus one manual filteras bypass filter (in parallel). Oftenthere also is a manual filter built onthe engine. This is a commonfeature on engines operating onheavy fuel oil.

• One automatic backflushing filter as main filter, followed bytwo parallel manual filters as indicator filters. The twoindicator filters may be built in one unit designated as aduplex indicator filter. This is a common feature on enginesoperating on heavy fuel oil.

Lubricating oil filtration

Filtersystem

Lubricating oil sumpPump PumpCoolerCooler Heater

100%

Centrifugal separator

Dieselengine

Figure 25.The completelubricating oiltreatment system.

Mainfilter

Main filter

Indicator filters



Designation and operation conditions for Alfa Laval lubricating oil filtersThe denomination of lubricating oil filters is built up in thefollowing manner:

Single or module filter:Protector T 280 D 50 / 8 A071 2 4 5 6 7 8

Duplex filter:Protector T L 280 D 50 / 8 A071 2 3 4 5 6 7 8

1 Generic name for the Alfa Laval filters

2 Type of main filterT Automatic filter for Trunk Piston EnginesX Automatic filter for Crosshead EnginesL Manual filter

3 Type of secondary filter (if duplex filters only)T Automatic filter for Trunk Piston EnginesX Automatic filter for Crosshead EnginesL Manual filter

4 External diameter of the filtering elements (automatic filters),of the filter insert (manual filters). Dimensions: 120, 140, 150, 240, 280.

5 Type of diversion chamber– No diversion chamberD Filter with diversion chamberC Filter with centrifugal separator

6 Automatic filters: Number of full-flow filtering elements (total number of elements for module filters).

Manual filters: Filtering area in dm3 (total surface area ofmodule filters).

7 Number of diversion elements (if applicable).

8 Filtration code.

Alfa Laval lubricating oil filters can be equipped with differentfinenesses of filter screens. The filter fineness is specified bythe engine manufacturer. A sketch of an Alfa Laval lubricatingoil filter installation is shown in Figure 26.

The filter normally has a pressure drop between the oilentering the filter and the clean oil (P1–P2) of 0.2–0.5 bar.The amount of filtered oil needed to backflush the filter screenand drive the hydraulic motor (Q3) is between three and fivepercent of the oil entering the filter.

For reliable backflushing and driving of the hydraulic motor, itis important to have a pressure difference of at least 1.4 barfor crosshead engines and 2.8 bar for trunk piston enginesbetween the filtered oil and the oil returning to the sump(P2–P3).

Dieselengine

Filter

2

3

Cooler

Lubricatingoil sump

Pump

Stand-bypump

1

Figure 26. Installation flow sheet for Alfa Laval lubricating oil filter.



Alfa Laval lubricating oil filters for crosshead enginesThe Alfa Laval lubricating oil filters for crosshead enginesdiffer from those for trunk piston engines. Higher flow rate ofthe lubricating oil, different demands on filter fineness,properties of contaminants, low oil pressure at the inlet to theengine, etc., are factors that require additional lubricating oilfilter specifications on the part of the engine manufacturer.

Pre-lubricationIn some installations the filter must operate during pre-lubrication. (The engine is stopped, but the lubricating oil ispumped with reduced capacity through the engine for rapidstartup.)

This can influence the filtering process. If the pre-lubricationperiod is longer than 24 hours and the pressure differencebetween the cleaned oil and the return oil to sump (P2–P3) isless than 0.8 bar, the pressure difference is not sufficient tooperate the automatic filter.

In this case an additional filter has to be installed in aseparate prelubrication circuit.

Dimensioning criteria for Alfa Laval lubricating oil filtersWhen dimensioning a lubricating oil filter, parameters such asfilter fineness, fuel oil type (heavy fuel oil or marine diesel oil)and type of engine (trunk piston engine or crosshead) aretaken into consideration as well as specifications from enginebuilders.

The specific load measured as litres of oil per squarecentimetre of the effective filter area and hour is presented inTable 1.

Type of engine Type of fuel Specific load Nom. filter fineness Abs. filter fineness(l/cm2 per hour) (µm) (µm)

Trunk piston Marine diesel oil 6–10 10–30 25–45Trunk piston Heavy fuel oil 5–8 10–30 25–45Crosshead Heavy fuel oil 10–16 20–35 35–50

Table 1. Specific load (l/cm2 effective filter area per hour) for lubricating oil filters. The figures are given in intervals, depending on which filtering fineness is chosen.



GeneralA complete fuel oil treatment system for a diesel engineconsists of a cleaning system, in which the separators areincluded, and a conditioning system.

The conditioning system includes filters to remove particlesand impurities that may have entered the system after theseparators. Since the filters are intended to protect theengine, they should be installed as close to the engine aspossible. An additional filter immediately before the engine isoften included in the engine supply. A typical fuel oil treatmentsystem for heavy fuel oil is shown in Figure 27.

Some engine builders recommend placing the filter upstreamfrom the deaerator tank (No. 7 in Figure 27). When the filter isplaced in this position the fuel oil flow through the filter issmaller, since there is no recirculation of oil as is the casedownstream from the deaerator tank. Also the oil viscosity ishigher since the temperature is lower. Both these factors aretaken into consideration when calculating the throughputcapacities. If the filter is placed upstream from the deaeratortank, placement of an additional filter downstream from thedeaerator tank is recommended.

For a heavy fuel oil installation, an automatic filter is oftenplaced in parallel with a manual bypass filter (Figure 28).

Due to the construction principle of the Alfa Laval filter, the oilpressure into the engine is not affected when the filter isbackflushed.

For fuel treatment installations designed for handling highviscosity fuels (up to 700 cSt at 50°C), the operatingtemperatures for the fuel oil filter can be as high as 160°Cdownstream from the deaerator.

Fuel oil filtration

6

7

8 91

2

2

3

3Settling

tank

Servicetank

5

4FM

2

2Dieselengine

1. Feed pumps2. Heaters3. Separators

4. Supply pumps5. Automatic filter6. Flow meter

7. Deaeration tank8. Circulating pumps9. Viscosity transmitter

(Indicator filter is optional)

Figure 27. Fuel oil treatment system with filters situated on the “cold” side. Filters can also be installed on the “hot” side.

Figure 28.Automatic fueloil filter with amanual bypassfilter (duplexfilter unit).



Due to the high operating temperatures, the filter is alsoavailable with an electrical motor drive for the distributorrotation, replacing the hydraulic motor. This motor assemblyis designed specifically for low-speed and high-temperatureoperating conditions.

This arrangement provides simplified maintenance andassures rotation of the distributor even in the most arduousoperating conditions.

The motor can be supplied for 110 or 220 VAC supply, 50 or60 Hz, and it draws around 0.1A to 0.4A according to filtersize and current during normal operation.

The electrical motor can be upgraded onto existinginstallations using a simple upgrade kit available for mostmodels.

Designation and operating conditions for fuel oil filtersThe denomination of fuel oil filters is built up in the followingmanner:

Single or module filterProtector F 150 D E 30 / 12 A051 2 4 5 6 7 8 9

Duplex filterProtector F M 150 D E 30 / 12 A051 2 3 4 5 6 7 8 9

1 Generic name for the Alfa Laval filters

2 Type of main filterF Automatic fuel oil filterM Manual fuel oil filter

3 Type of secondary filter (if duplex filters only)F Automatic fuel oil filterM Manual fuel oil filter

4 External diameter of the filtering elements (automatic filters),of the filter insert (manual filters). Dimensions: 120, 140, 150, 240, 280.

5 Type of diversion chamberD filter with diversion chamber

6 Type of driving motor for backflushing– Hydraulic motorE Electric motor

7 Automatic filters: Number of full-flow filtering elements (total number of elements for module filters)

Manual filters: Filtering area, in dm3 (total surface area ofmodule filters)

8 Number of diversion elements (if applicable)

9 Filtration code

The use of the electrical motor means that this filter is suitablefor “hot” and “cold” side installations, according to customerrequirements and without limitations.

To ensure proper backflushing (and rotation of the hydraulicmotor on the automatic filter when fitted), it is important thatthe pressure difference between the filtered oil and the oilgoing back to the suction side of the fuel oil pump (P2–P3) isat least 2 bar. For this reason the viscosity of the fuel oilshould also be below 75 cSt when the filter is placed down-stream from the deaerator tank (150 cSt upstream from thedeaerator tank). In contrast to the lubricating oil filter, thehydraulic motor of the fuel oil filter is driven by the filtered oilfrom the diversion chamber.

The pressure drop between the unfiltered and filtered oil(P1–P2) is normally 0.2–0.5 bar. The necessary amount of oilfor backflushing the filter is approximately 15 percent of theoil flow entering the filter. The same oil that is used forbackflushing is also used to drive the hydraulic motor.

Another factor that influences the sizing of the filter is thefineness of the filter screen. This is determined by therequirements of the diesel engine manufacturers. The filtersize for a given fuel flow increases when a smaller filter screenis used, due to the fact that the number of particles collectedon the filter screen will increase.

Dimensioning criteria for Alfa Laval fuel oil filtersThe maximum allowed load for a fuel oil filter depends onwhich type of fuel is filtered and filter fineness. Due to the oilflow, the filter size can roughly be calculated from Table 2below. Note that the oil viscosity through the filter is less than75 cSt and that P2–P3 ≥ 2 bar.

Type of fuel Specific load Nom. filter fineness Abs. filter fineness(l/cm2 per hour) (µm) (µm)

Marine diesel oil 4–8 10–30 25–45Heavy fuel oil upstream 2–3, downstream 3–6 10–30 25–45

Table 2. Specific load (l/cm2 effective filter area per hour) for fuel oil filters. The figures are given in intervals, depending on which filter fineness is chosen. (Note! Upstream viscosity ≤ 150 cSt. Downstream viscosity ≤ 75 cSt, P2–P3 ≥ 2 bar.)

Alfa Laval reserves the right to make changes at any time without prior notice.

Any comments regarding possible errors and omissions or suggestions for improvementof this publication would be gratefully appreciated.

Copies of this publication can be ordered from your local Alfa Laval company.

Published by: Alfa Laval Tumba ABMarine & Diesel EquipmentSE-147 80 TumbaSweden

© Copyright Alfa Laval Tumba AB 2004.

EOEM00012EN 0406

Alfa Laval in brief

Alfa Laval is a leading global providerof specialized products and engi-neering solutions.

Our equipment, systems and servicesare dedicated to helping customersto optimize the performance of theirprocesses. Time and time again.We help our customers to heat, cool,separate and transport productssuch as oil, water, chemicals, bever-ages, foodstuff, starch and pharma-ceuticals.

Our worldwide organization worksclosely with customers in almost 100countries to help them stay ahead.

How to contact Alfa Laval

Contact details for all countries arecontinually updated on our web site.Please visit www.alfalaval.com toaccess the information.

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