Primary Fuel Filter Element Specification

The specs for primary fuel system elements are as below:

  • 10 Micron Nominal Filtration
  • For additional information see SENR9620 Fuel Systems – Improving Component Durability

Duplex Fuel Filters
Many Cat engines can be equipped with duplex fuel filters as shown in Figure 8.

These filters may be serviced (change elements), without shutting off the engine. There are two types: the symmetrical type, which has two identical filter sets and the main-auxiliary type, which has a main filter set and a smaller capacity
auxiliary filter set. A special valve connects the two sets of filters in each type. The valve routes the fuel to be filtered through either or both sets of filters.

Both filter sets can be used simultaneously to extend running time in an emergency.

  • Duplex filters for fuel and lubricating oil allow extended operation without interruption.
    The main and auxiliary filter systems allow changing either the main or auxiliary filter elements with the engine running under load.
  • Generally, the same elements are used in both systems, and are capable of providing adequate filtration for at least 100 hours full load running time with reasonably clean fuel and oil.
  • Use pressure gauges to determine when filters must be changed.
  • Avoid mounting filters near the radiator fan, because a fuel or oil leak during replacement could create a fire hazard. (As either substance passes through the fan it can be atomized, and therefore easier to ignite.) Plus, coated radiator fins trap dirt which can diminish cooling capability.

Water Separation
Water in the diesel fuel is absolutely unwanted as it will cause damage to the engine and its components. Water
appears in the fuel because of condensation, handling and environmental conditions. Environmental conditions
relate to the humidity of some climates. Water in the fuel will be more prevalent in humid climates.

Water can impact the fuel system in the following ways.

  • If water appears in the injection system, the fuel will not be able to lubricate as it is supposed to
    and it will lead to early wear.
  • Water together with diesel fuel will form microbiological growth which will build up sludge. Sludge will cause wear of the filter system and influence the injection performance.
  • Iron will oxidize when in contact with water and can infiltrate the fuel. The iron oxide will cause injector wear.

Engines using high injection pressure fuel pumps must be protected from water and sediment in the fuel. It is extremely important to maintain water and sediment levels at or below 0.1%.
Note: Water and sediment collecting in fuel tanks may give the appearance that poor quality fuel was delivered to the site.

Several methods can be used to remove excess water and sediment from the fuel system:

  • A water and sediment separator can be installed in the supply line ahead of the transfer pump. The separator
    must be sized to the handle the fuel being consumed by the engine as well as fuel being returned to the tank.
  • Coalescing filter systems work effectively to remove sediment and water. If the level in the day tank is not maintained at a consistent level, install them between the main tank and the day tank. If proper day tank levels are maintained, a smaller system can be used between the main tank and the day tank to clean only the fuel being burned. These filters can plug and careful attention must be given to fuel pressure levels at the injectors to guard against misfiring.
  • A centrifuge system can be used, particularly if the fuel quality consistently falls below the defined limits
    discussed in this guide.


The centrifuge represents the most expensive and complex method of water separation, but it is the most effective. It is used extensively in marine, offshore and power generation applications where a continuous power supply is essential,
and the continuous supply of clean fuel cannot be left to chance. A typical distillate fuel centrifuge schematic is shown in Figure 9.

A centrifuge manufacturer should be consulted to determine the proper centrifuge type, size and flow requirements for a specific application.

While Figure 9 shows a single centrifuge schematic, many applications will require the use of two (2) centrifuges, with one of the centrifuges acting as a standby.

The required flow rate of a centrifuge can be approximated as follows:

Q= Flow required, L/hr
P= Total Engine Output, kW
b= Fuel Consumption, g/kW-hr
R= Density of fuel, kg/m3
T= Daily separating time in automatic operation: 23 hr


28. April 2021 by samuel
Categories: Diesel Fuels & Diesel Fuel Systems | Comments Off on Primary Fuel Filter Element Specification