AIR VENT
FROM
INTAKE MANIFOLD
FROM
GASOLINE
SUPPLY TANK

Fig. 50. Vacuum System—Top Arrangement

[Fig. 50] shows the top arrangement and connections. R is the air vent over the atmospheric valve. The effect of this is the same as if the whole tank were elevated, and is for the purpose of preventing an overflow of gasoline, should the position of the car ever be such as to raise the fuel supply tank higher than the vacuum tank. D shows the pipe connection from the fuel supply tank. C shows the pipe connection to the intake manifold. W shows a tap or vent through which gasoline may be fed into the upper chamber, in case the fuel supply tank is damaged or put out of commission. R shows the air vent connection from the lower tank.

[Fig. 51] shows a general diagram of vacuum system installation. One of the chief advantages is that it allows the carburetor to be placed near the head of the motor and does away with the long manifold connections required with the gravity feed systems. This also reduces the frictional resistance, gives a richer mixture and greater volume of flow.

AIRVENT
A—CONNECTION
BETWEEN INTAKE
MANIFOLD AND
VACUUM TANK
C—CONNECTION
FROM VACUUM
TANK TO CARBURETOR		B—
CONNECTION
BETWEEN
MAIN GASOLINE
SUPPLY TANK AND
VACUUM TANK

Fig. 51. Vacuum System Installation

[Fig. 52] shows a sectional view of the Stewart Vacuum System and explains the operative value of each part. A is the suction valve for opening and closing the connection to the manifold through which a vacuum is extended from the engine manifold to the gasoline tank. B is the atmospheric valve, and permits or prevents an atmospheric condition in the upper chamber. When the suction valve A is open and the suction is drawing gasoline from the main supply tank, the atmospheric valve B is closed. When the suction valve A is closed, the atmospheric valve B must be open, as an atmospheric condition is necessary in the upper tank in order to allow the gasoline to flow through the flapper valve H into the lower chamber. C is a pipe connecting the tank to the intake manifold of the engine. D is a pipe connecting the tank to the main fuel supply tank. E is the valve control lever and has two coil tension springs S attached to operate the short valve lever F. G is the metallic air-containing float, which controls the action of the valves through the spring and lever arrangement. H is the flapper valve at the outlet of T, and it closes by suction when the vacuum valve A is open. When the vacuum valve A closes, the atmospheric valve B opens and relieves the suction in the upper tank, the flapper valve H opens and allows the fuel to flow from the upper tank into the lower chamber.