Diesel Fuel Filters | All You Have to Know.

D(caps)iesel fuel filters are an essential component of a diesel engine’s fuel system. They are responsible for removing impurities and contaminants from the diesel fuel before it enters the engine. Diesel fuel contains various impurities such as water, dirt, rust, and other contaminants that can damage fuel injectors and other engine components. The diesel fuel filters trap these contaminants and prevent them from reaching the engine.
Diesel fuel filters.
Diesel fuel filters.


In this article, I will discuss full details about diesel fuel filters. 

Diesel fuel filters

Dirt carried in the fuel is recognized as a prime source of trouble and inefficiency in diesel engine operation, as it is the cause of wear in the fuel injection pump and nozzles. The fuel injection pump is a sturdy, well-designed piece of equipment that will give trouble-free service for many thousands of hours running, provided the fuel is clean, but if dirt, especially fine dust, is allowed to pass into the system in the fuel, then wear follows with it irregular running and loss of power; maintenance costs will become heavy and engines will need frequent attention. Where sedimentation in the supply tank can be efficiently carried out, this will greatly reduce the amount of dirt carried in the fuel. Under working conditions, however, it is absolutely essential that the fuel be properly filtered before entering the injection pump.

Diesel fuel filters- method of operation- 

The fuel enters the filter bowl through the inlet connection, then passes through the filter element and leaves the filter through the outlet orifice completely clean. In multi-stage (dual) filters, the fuel oil flows first through the primary filter and then through the secondary micro filter before continuing to the fuel injection pump.


Prior to putting it into operation or after cleaning and changing the filter element the filter must be filled with fuel oil through the filler plug orifice on the filter cover. After filling, the filler plug should be replaced immediately and the filtered air vented.

Diesel fuel filters diagram.
Diesel fuel filters diagram.


The importance of care in replacing the element, and avoiding getting dirt on the clean side of the filter, cannot be over-emphasized, as many complaints of fuel pump element wear can be traced to a lack of care in the servicing of filters. When choking takes place, this is usually found to be due to a waxy sludge which is deposited from the fuel. If filters are found to choke in an unreasonably short time this will probably point to an unsatisfactory fuel supply or storage tank installation and should be taken to find out how and a what point an undue amount of impurities can enter the system.

Paper elements are not intended to be cleaned and must be discarded when choked. The cost of replacement elements has been kept down to the lowest possible figure compatible with special care in manufacture and compares more than favorably with other less efficient filtering elements. The number of filters used for any engine installation will obviously depend upon the capacity of the particular engine and the conditions of operation. In all cases, the main objective is to provide the highest possible degree of filtration consistency with long filter element life.
Due to the widely differing conditions of operation that have to be catered for, precise instructions for servicing intervals cannot be stated for paper elements; and operators are advised to follow in the first place the recommendations laid down in the vehicle, tractor, or engine instruction book. The period at which it will be found necessary to change the filter element will naturally vary according to the type of fuel used, provision made for bulk storage, setting or pre-filtering before filling the vehicle tank, and the local conditions under which the engine concerned is working. This may easily be as short as three months or as long as twelve months, but it is not expected that it will be outside this period although exceptional circumstances may make it so.
The filter inserts should never be cleaned. Every 5,000 km or 125 hours of operation, the filter bowls should be drained to remove sediments/water. Since filter inserts attain maximum efficiency only after a film of dirt has deposited on the surface of the filter insert, the stage I and stage II filter inserts should never be replaced at the same time. Sometimes, the filter inserts get clogged in a very short time due to asphaltene or waxy compounds present in the fuel. In such cases, the filter insert has to be replaced.

Diesel fuel filter inserts- 

Development over the years has led to the use of paper as the filtration media. Paper is particularly suitable because the important properties that determine filter quality, such as pore size and pore distribution, can be maintained effectively during manufacture. Moreover, a paper filter has a large surface area giving correspondingly longer service life. However, for first-stage filtration cloth pre-filter inserts are also used. 
Here are some diesel fuel filter inserts examples- 

1. Coil-type paper filter insert- 

Coil type paper diesel fuel filters insert.
Coil-type paper filler insert.


For coil-type filter inserts, the filter paper is wound around a tube, and neighboring layers are glued together at the top and bottom as shown in Fig This forms pockets with openings at the top. The fuel flows along the V-form coil axially from the bottom to the top and the dirt particles are held in the filter pockets.

2. Star-type paper filter insert- 

Star-type diesel fuel filters insert.
Star-type filter inserts.


In star-type filter inserts, the fuel flows radially from the outside to the inside. The paper folds are sealed at the top and at the bottom by end covers. The filtered fuel collects inside the perforated center tube and flows upwards. The dirt particles are trapped on the filtering surface or settle down at the bottom.

Principle of paper elements- 

The paper element wound around a circular core in the form of a spiral. contained in a thick paper or a thin metal canister. The winding is done in such a manner as to provide a very large filter area within minimum filter bowl dimensions, and actually gives six times the filter area of the normal cloth filter within a bowl of approximately two-thirds the size.
Spiral construction type diesel fuel filters insert.
Spiral construction.
This Fig shows diagrammatically the way in which the paper spiral is constructed. Dirty oil is confined to the undersides of the paper coils and filtered oil is to the upper sides. The large filtering surface will be apparent. 
Fuel flow through elements.
Fuel flow through elements.
This Fig shows the path taken by the fuel in passing through the element. The actual number of turns of paper is, of course, much greater than depicted in the diagram, the paper being would close but allowing continuous oil space between adjacent. 

3. Cloth-type pre-filter insert- 

Cloth type fuel filters type insert.
Cloth-type insert.


For the first stage of filtration, a cloth type of filter insert is used. these filter inserts are also available in 0.5 and 1.1-liter capacities. In cloth-type filter inserts the fuel flows radially from outside. The cloth is coiled around a perforated tube and the ends are sealed at the top and bottom by end covers. 


In addition, the fuel filters are as special as the air filters. Filters mean the filtering of micro and major particles coming from the media.  Here the media is fuel. 
Thanks for reading. 
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