FUEL PUMP INSTALLATION

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When my fuel pump died during a trip down Baja California, I stopped in Ensenada on the way back and found an auto parts store that had six volt Stewart Warner fuel pumps in stock. On returning home, I bought an adjustable fuel pressure regulator from J. C. Whitney.

The fuel pump was larger and heavier than the prior unit, so it required a supporting bracket. This was made from a small piece of angle iron that bolted to the bottom of the Model T frame, and the fuel pump was bolted to the bracklet. The adjustable pressure regulator was mounted to the fuel pump outlet with a short 1/8 pipe nipple. The 5/16 inlet and outlet fuel lines were connected to the assembly via 1/8 street pipe Ts so that a bypass line could be installed aound the fuel pump assembly. This is shown in Figure 1.

The prior fuel pump system used an orificed bypass line to regulate pump pressure and to provide a free flow of gasoline to the carburetor in case the pump was shut off or failed. The free flow feature had been useful in the past and that feature was to be retained. Fuel back flow to the pump input could not be allowed in the new installation as the pressure was to be controlled by the pressure regulator so that the pump could shut down except for when fuel flow was required. Backflow prevention required the use of a check valve. The very low gravity fuel head requires that the valve opens very freely, but it also must close easily when the fuel pump system is in operation. The pressure regulator is set at about 1/2 pound so that the carburetor inlet valve is not required to shut off against too high a pressure.

Several commercial check valves were tested, but they failed either to open easily or they could not shut tightly with the 1/2 pound back pressure. This car, a 1925 touring, has had a Grose Jet carburetor inlet valve in service for years without any problems, so it was decided to try the use of a Grose Jet as a check valve.

A housing was made out of brass pipe fittings as shown in Figure 2. The housing needed to have an adequate inside diameter to clear the outside of the Grose Jet valve, hence 1/4 inch pipe fittings were used. The two 1/8 to 1/4 bushings were dilled out a bit on the inside to provide the needed clearance. The upper inlet area was tapped so that the Grose Jet valve could be screwed in. The system, as shown in the figures, has been in service for six years without a problem. It is periodically tested by shutting off the fuel pump while driving the car.

As a matter of interest, the fuel pump system is connected to the carburetor via a marine grade fuel shutoff valve as shown in Figure 3. This valve opens and closes easily, even after many years of service. It has a positive shutoff and does not leak. The stub at the right in the figure is a fuel tap point that I have used to check system operation and to test the check valves during the design of this fuel pump system. A vertical tygon tube is connected to the tap as a stand pipe when it is desired to measure the fuel pressure head.


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