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Ellison Throttle Body Injector

Fuel Filtering

The Ellison Throttle body Injector (TBI) requires clean fuel for proper operation. A 70 micron filter is required to keep contaminates out of the TBI. The TBI does have a last chance fuel strainer installed on the fuel inlet fitting. This strainer is there only to trap large particles in the event of a primary filter failure. The strainer is fine enough to reduce the possibility of particles plugging the fuel metering tube but particles which can pass through the fuel inlet screen can keep the valve in the fuel regulator from closing completely. This can result in an erratic idle and fuel leakage after engine shutdown.  Many throttle body installations use a standard gascolater with screen before the fuel pumps to prevent large particles from damaging the fuel pumps and to provide a low point water drain, but then after the engine driven pump, a 70 micron filter or finer must be installed.

This filter must be carefully selected.  Some paper filters will not pass water and could cause fuel system blockage if saturated with water.  A drain must be provided and it must be drained before each flight.  If this filter is installed on the pressure side of the boost pump it must have sufficient strength to handle pump pressure without bursting or leaking. The Glassair III uses a Fram HPG 1 with a low point water drain added which is a very good filter housing and perfectly capable of operating with pressurized fuel.  As with all fuel system components, the filter must be located well away from sources of heat, preferably outside of the engine compartment.  If located in the engine compartment it must be blast cooled to prevent vapor formation.

An excellent article about fuel system design by Lyle Powell, may be accessed by clicking on Fuel Systems for Homebuilt Aircraft.

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