Fuel/Water Separators

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

3. “Location can impact performance when air or fuel leaks arise,” Braswell says. “Fuel/water separators are predominately located on the suction side of the lift pump, so any leaks will result in air being sucked into the fuel while the engine is running. These same types of leaks can cause fuel leakage when the engine is shut down.”

To minimize these types of problems, TMC says consider the following:

When changing filters, replace all seals included with replacement kits and tighten spin-on filters or cartridge covers to the recommended torque value specified by the manufacturer.

Check the connection fittings and ensure that thread sealant is used on pipe thread fittings. If straight SAE fittings are used, ensure that seals are in good condition. Some fuel lines are fabricated from plastic hose with push locks or compressions. “Don’t overlook the hose-to-fitting connection as a possible leak point when diagnosing air leaks,” says Braswell.

4. Select a device with a large enough water sump capacity to coincide with expected water drain intervals for a given operating environment.

5. Pay attention to the installation and routing of fuel fittings and fuel lines. When installing fittings, paste type thread sealant should be used on clean threads. Proper torque is to be used, particularly with plastic housings.

Ninety-degree fittings should be avoided when ever possible, says Braswell, so as not to add any unnecessary restriction. If use of 90-degree fittings is unavoidable, use the next larger size.

For example, a fuel system that flows 120 gallons per hour using two 90-degree fittings with a 1/2-inch diameter will add 0.5 inches of mercury restriction. If the diameter of the two fittings was increased to 0.625 inch, the restriction will be reduced to 0.2 inches of mercury.

“Fuel flow rates of given engines vary substantially from manufacturer to manufacturer,” Braswell says. “It is of prime importance that the flow rate be known in every instance and a fuel/water separator of corresponding capacity be used.

“The engine manufacturer will be able to provide information to specific flow rates and, allowable pressure drop - resistance in fuel flow. When mounting of the fuel/water separator necessitates a substantially longer fuel line, consideration should be given to using the next larger size line.

Additional information and spec’ing tips can be found in TMC RP 317A, “Fuel/Water Separation Devices.” It is published in TMC’s 2010-2011 Recommended Practices Manual. TMC RP 317A is also available separately from TMC. For more information, call TMC at (703) 838-1763 or visit TMC’s website at tmc.truckline.com.

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