The Stewart tank (Fig. 230) is mounted in a wood seat frame. However, steel straps are attached to the tank and form brackets which rest on wood sills.
The Autocar tank (Fig. 231) is formed from a sheet but the ends do not lap, as a pressed cover is used. The heads are also pressed and set into the body. This construction permits riveting and soldering the head and all parts, while the cover which receives very little strain is soldered. This tank is mounted on steel brackets riveted to the frame and is retained by two rods which are supported by two brackets riveted and soldered to the tank.
Several makers use tanks which are drawn from one sheet of metal and have but one soldered joint. This type of tank is illustrated in Fig. 232, which illustrates the mounting of the United States trucks. These tanks are tinned inside and out and the head is soldered as shown.
The United States mounting consists of a separate frame or cradle, very rigid, having two brackets which rest on the vehicle frame, connected by a steel channel and a tie rod. Raybestos is riveted to the brackets to give a cushion effect, and the tank is retained by two steel straps. Gasoline feed is by gravity through a strainer attached to the tank and supported from the tank mounting.
Gasoline tanks when soldered and placed under the seat, have given some trouble due to leaks, as in some cases it is quite difficult to hold the tank in such a way as to prevent vibration from cracking the solder at the joints. The gasoline supply pipe also has its disadvantages since when the motor is placed under a hood, this pipe becomes quite long and it is difficult to keep it free from leaks.
In order to overcome these objections these tanks on the Denby and Union trucks are mounted on the dash, the Union mounting is illustrated in Fig. 233. This position provides the shortest gasoline line, reducing the danger of leaks due to vibration. while it also provides an ample head of fuel for gravity feed. This tank is supported by brackets and straps and is provided with a strainer and shut-off valve. In the pressure feed system either the pressure of the exhaust gases or air pressure from a mechanical driven pump is used to force the gasoline to the carburetor fload chamber. This system requires considerable piping, a pressure gage, a pressure regulator or pump and a hand pump. Stewart Vacuum Feed. - The Stewart vacuum feed is used on the Knox tractor. Kissel Kar trucks and others and is shown in Fig.234 The mechanism is contained in a cylindrical tank which may either be mounted on the engine or on the dashboard.The tankisdivided into two chambers. the upper one being the filling chamber and lower the emptying chamber. The former contains a float valve and the connections to the intake manifold and the main . fuel tank. The lower chamber has a connection leading to the carburetor. This lower chamber is always under atmospheric pressures as the flow of gasoline from it is by gravity only. Atmospheric pressure is maintained by an air vent which communicates with the chamber. The suction of the piston on the intake stroke creates a vacuum in the upper chamber, which closes a valve between the two chambers and in turn draws gasoline from the main tank. The gasoline, as it is being sucked into the upper chamber operates a float valve. When this float valve has risen to a certain mark, it automatically shuts off the suction valve and opens an air valve. This open air valve creates an atmospheric condition in the upper chamber and gasoline immediately commences to flow to the emptying chamber. When the float is at the bottom of its chamber, the suction valve is open and the air valve is closed. The lower chamber has a flap valve which prevents the gasoline in the lower chamber from being sucked into the upper chamber, as the float falls and opens the suction valve.
On the Knox Tractor the gasoline tank is mounted on the running board and the engine suction through the system described above draws gasoline from the main tank and supplies the carburetor.
Fig. 230. Stewart Gasolene Tank and Mounting.
Fig. 231. Autocar Tank with Riveted and Soldered Ends.
Fig. 232. U. S. Pressed Steel Tank and Mounting.
Fig. 233. Union Tank Mounting.
Fig. 234. Stewart Vacuum Tank.
The Saurer truck uses a pressure feed, the gasoline tank being located under the driver's seat and above the level of the carburetor when the tank is full. On the special Saurer carburetor, however, it was found that a constant pressure was essential to its proper functioning and the gasoline tank was moved from the rear of the truck to the driver's seat. Fig. 235 is a cross-section of the exhaust pressure device.
The exhaust gas enters and passes through a screen to remove carbon and fire, any small particles falling to the bottom of the long tube which can be removed for cleaning. The gas then passes to the other chamber through the valve which it lifts, The valve is returned to its seat by a spring to retain the pressure in this chamber and prevent its escape back into the exhaust manifold in the interval between exhausts. The upper valve is a sort of safety valve to prevent the pressure from becoming too great. This valve is regulated by the knurled screw on top of the device. The pressure is maintained at about two pounds.
Fig. 235. Saurer Pressure Device.
Each system has its advantages and its disadvantages. Gravity is an absolutely dependable and constant force which acts independently of an artificially created condition, and can be implicitly relied upon to cause the flow of fuel to the carburetor so long as the pipe is unobstructed and the upper surface of the fuel supply is at a higher level than the gasoline level in the carburetor float chamber. It is the most simple system on account of the simplicity of piping and fittings and there is practically nothing to keep in order.
The chief disadvantage is that the pressure under which the fuel is supplied to the carburetor is variable. Not only does it diminish progressively as the fuel level in the tank falls, on account of the reduction of the gravity head acting, but it also diminishes whenever that portion of the vehicle which carries the tank stands at a lower level than that which supports the carburetor.
With a forced system, as long as the artificial pressure is maintained, there is almost a certainty that gasoline will constantly be fed to the carburetor entirely independent of every other conditions.
The system possesses disadvantages in that there are numerous pipes and joints which must be kept tight in order that the tank may hold its pressure and the multiplicity of pipes and fittings adds to the possibility of leaks clue to vibration.
The vacuum system is by far more simple than the forced system and eliminates the pressure pump, gages, regulator, a number of fittings and an air-tight tank. Leaks in pipes are materially reduced as the pressure is very low. Like the forced system it will supply gasoline to the carburetor regardless of grade, vehicle position or head of gasoline in the main tank.
This vacuum tank must not be installed in the exhaust side of the engine, as gasoline may leak or overflow from the tank and cause explosions or fires. Proper operation of the system depends entirely upon the float valve and if it develops a leak it cannot shut off the suction valve as it becomes too heavy to rise. Particles of dirt may also cause trouble by holding the flap valve open, which will render the system inoperative. The piping is also subject to the danger of vibration.