The function of the fuel supply system of a commercial car is to furnish the carburetor with an unfailing supply of gasoline until the supply carried is entirely exhausted. This must be done independently of the grades encountered by the vehicle. The gasoline is generally fed by gravity from the tank to the carburetor, although one maker uses pressure feed, while several others use the vacuum system, which has been so successful on pleasure vehicles.
In the gravity system the "head" of fuel is depended upon to feed it to the carburetor. Tank location therefore is an important phase of this system, and requires the tank to be elevated above the carburetor. With this system the tank may either be placed on the dashboard or under the driver's seat. In a pressure feed system the tank may be located at any level with reference to the carburetor, since the fuel is always under a predetermined pressure sufficient to maintain a constant level in the carburetor float chamber. This pressure may either be obtained from the exhaust or by a special air pump.
In the vacuum system the suction of the engine is used to draw gasoline from the supply tank to an auxiliary tank, from which the gasoline flows by gravity to the carburetor.
Gasoline tanks are generally made from tinned sheet steel, known as terne plate, and may either be pressed or formed to shape with ends and joints soldered or riveted and soldered. In order to provide the maximum mileage for a vehicle, they must be made to hold from twenty to thirty gallons and must be reinforced, so that the ends are protected from being forced out as the fuel rushes from one end to the other. These reinforcements or baffle plates also serve to prevent rattling due to vibration and sagging at the center of the tank. They are provided with holes or openings so that the gasoline can find a level in all compartments.
The filler cap and outlet are usually provided with strainers which are made from metal gauze, while shut-off cocks are provided in the outlet to shut off the supply. Some makers also provide a reserve supply in the tank. This is usually accomplished by a three-way cock fitted with a stand pipe which projects several inches above the bottom of the tank. Ordinarily the gasoline passes through this stand pipe, but when the lock is turned to the reverse position, the fuel is permitted to pass through another opening flush with the bottom of the tank. These features are shown in the following illustrations.
Fig. 225. Nash Quad Gasolene Tank and Gravity Feed System.
Fig. 225 illustrates the Nash Quad gasoline tank and the feed pipe and carburetor. This also serves to illustrate the conventional gravity feed system. The filler cap is located near the center of the tank and is provided with a large handle so that it can easily be removed. A large strainer fits inside of the filler flange, which is riveted and soldered to the tank. The body of the tank is of rectangular shape and formed from a sheet of steel. The head is set in lapped and soldered as shown in the small sectional view. Two outlets with shut-off cocks are provided, so that gasoline may flow from either or both ends. Each of these cocks are provided with two openings level with the bottom of the tank for the reserve supply, while the regular supply is taken through the stand pipes.
Fig. 226 shows the Riker tank and mounting. This tank is of the bolster type, or modified rectangular shape and provided with two baffle plates for reinforcements. The heads are dished outward and the edges of the body are flanged over them and soldered. Both filler and outlet are provided with strainers, and two handles are soldered to the top of the tank so that it can easily be removed for repairs. The upper views show the method of mounting the tank in a steel compartment which supports the drivers seat. This compartment is made of sheet steel and a framework of small angles riveted together. Angles on the front and rear near the bottom support brackets which carry the tank. A strip of felt is placed between the brackets and the tank to from a cushion and steel straps hold the tank in position.
Fig. 226. Riker Gasolene Tank and Mounting.
Fig. 227. Peerless Gasolene Tank Support.
Fig. 227 depicts the Peerless mounting. However, this differs from the above in that the tank, which is of cylindrical form, is supported and retained by steel straps. It is carried in a steel compartment supporting the driver's seat.
The Pierce tank is of rectangular shape and supported from the frame by means of sheet steel brackets and wood blocks as shown in Fig. 228. This mounting is so constructed that the framework which supports the seat surrounds the tank. A reserve compartment is provided and arranged, accessible through a handle outside of the seat compartment. Gasoline feed to the carburetor is by gravity and a connection is also made for priming the engine in cold weather. A hand-operated priming pump is attached to the scat compartment and supplies a small quantity of gasoline to the motor through the intake manifold.
On the Kelly trucks the seat compartment is also made of wood and the rectangular-shaped gasoline tank fits snugly in this. It is supported by wood beams at each end and at the center. The tank is placed well above the carburetor to provide the proper head as shown in Fig. 229. It is retained by wood strips and protected from excessive heat by a steel plate at the bottom, which provides an air space under the tanks.
Fig. 228. Pierce-Arrow Gasolene Tank and Mounting.
Fig. 229. Kelly-Springfield Gasolene Tank Mounting.