Fuel/Water Separators

5 ways to combat water in fuel from the Technology & Maintenance Council


Among TMC’s many Recommended Practices (RP) is one that offers guidelines and advice on how to best specify fuel/water separating devices used on heavy duty, diesel-powered commercial vehicles. Newly revised, it is TMC RP 317A, “Fuel/Water Separation Devices.”

To combat water in fuel, TMC offers the following recommendations:

1. Select a micron rating and water separation performance level that meets the engine manufacturer’s recommendation. “Choosing filters with unacceptably low particle efficiency may result in fuel system damage,” points out Braswell. “Conversely, filters that are too efficient may result in unacceptable short service intervals.”

Short filter life may be caused by factors that cannot be controlled by equipment owners/users, such as dirty fuel and/or unstable fuel that breaks down and plugs filters, he says. However, there are some measures that can be taken to minimize other causes of short filter life. For example:
If filters plug prematurely due to dirty fuel, specify that filters be used on dispensing pumps to pre-filter the fuel.

Contact your fuel supplier for information on how to test fuel tanks for microbiological growth and remedies to eliminate it.

In cold weather wax can build up on the filter from the fuel. Fuel/water separator heaters and/or fuel additives are available to minimize waxing problems.

Do not use a filter with a micron rating higher than that recommended by the engine manufacturer in an effort to solve short filter life unless there is another filter downstream to perform the final filtration.

2. Pay close attention to location and mounting considerations, counsels Braswell. Fuel/water separators are designed to allow a high level of mounting flexibility. Therefore, keep the following in mind when spec’ing location and mounting:

Fuel/water separators should be located at or below the level of the fuel pump to avoid air problems.

The inlet of the fuel/water separator should not be mounted below the top of the fuel tank to prevent fuel from siphoning from the tank when the unit is serviced.

If the fuel/water separator inlet cannot be installed above the tank, a shut-off valve must be installed close to the fuel/water separator.

The most desirable location for a fuel/water separator is inside the engine compartment, where maximum protection from wind and weather is realized.

If a fuel heater is used, the fuel heater should be located before and near the fuel/water separator. Many devices have built in options for co-location.

In areas of extreme low temperature, fuel lines and fuel/water separator insulation may be necessary.

When a fuel/water separator is directly mounted to the engine or other high vibration area, consideration should be given to bracket design and stress on fittings and lines, as well as to filter performance.

The mounting location should be accessible for service and draining. Most separators are mounted on the frame rail, which makes servicing easier and less time consuming.

Avoid positioning in an area of extreme heat.

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