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Stewart

The operation of the Stewart vacuum tank is explained in the illustrations and text below as follows:
Fig. 5. View showing interior of vacuum tank with mechanism in position at the start of the cycle of operation. Float (A) is in its lowest position. Springs (B) are below valve lever pivot(C), producing a tension downward on the valve stem lever, holding the atmospheric valve (El closed and the vacuum valve (D) open.
Air is being exhausted from inner vacuum, or operating chamber (M). Flapper valve (F) is closed, because pressure inside of outer reserve chamber (N) is greater than that inside of operating chamber (M).
Gasoline (G) is flowing into operating chamber(M).
Fig. 6. View showing float (A) rising due to gasoline (G) flowing into operating chamber which raises the level of the gasoline. Note that springs (B) are also moving upward with their fulcrum (H) at the extreme right end. Vacuum valve (D) still open, atmospheric valve (E) closed; flapper valve (F) still closed.

Fig. 7. View showing float (A) still rising and in a higher position. Springs (Si are now slightly above center of valve lever pivot (C), producing a slight tension in an upward direction. This will cause the lever to snap upward (see view ill Fig. 8). Vacuum valve (D) still open, atmospheric valve (E) closed, flapper valve (F) still closed.
Gasoline (G) flowing into operating chamber.

Fig. 8. View showing float (A) in highest position. Springs (B) above valve lever pivot (C) ; lever having moved upward thus closing the vacuum valve (D) and opening the atmospheric valve (E) to the operating chamber.
Gasoline ceases to flow from the main tank as the suction is broken. Atmospheric pressure (see pages 1073, 113 for meaning) now exists in both operating and reserve chambers.
The level of the gasoline in the operating chamber (M) being higher than that in the reserve chamber (N), causes the gasoline to flow into the reserve chamber (N) through the flapper valve (F)

Fig. 9. View showing float (A) descending, with level of gasoline in operating chamber lowered to a point where the float (A) and springs (B) are in position, producing a tension below valve lever pivot (C), which will move the valve lever downward, opening the vacuum valve (D) and closing the atmospheric valve (E), at which time the operation shown in Fig. 5 will take place again.

Note: The reference letters on above illustrations differ from those in preceding illustrations (except M and N which correspond). The vacuum tank shown in Fig. 1 page 1303, is a later development and has the improved float operating mechanism (see T, Fig. 1, page 1303 and Fig. 3, page 1304). The principle of operation is the same however.

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