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Nothing New Under The Sun: Innovative Stewart-Warner Gasoline Feed by Vacuum

Many of our readers are familiar with the early Stewart-Warner Vacuum Tank, and other means of fuel delivery before the conventional diaphragm fuel pump came into use in the early-1930s. Today’s feature covers the device in detail for the benefit of readers who would like to know more about how it operates and and for others unaware of its place in automotive history.

The earliest automobiles generally used fuel delivery by gravity feed, air pressure supplied by a hand pump, devices that used exhaust system back pressure, and air pumps operated by a dedicated lobe on a camshaft. All of these methods had limitations and issues that will not be covered here today.

The lead image taken at the 1917 New York Auto Show contains a mock-up show exhibit by the Stewart Co. (later Stewart-Warner) with a large vacuum tank assembly inside of a glass cylinder and two production models mounted on the firewall, and a Company spokesman and model.

Located inside of the vacuum tank assembly is the operating mechanism that is attached to the lower side of the cover. The bottom portion of the tank stores the fuel delivered by vacuum sourced from the intake manifold. Gasoline then flows by gravity to the carburetor. The expandable image (above) contains a detail view of all three of the display units.

Share with us what you find of interest in the photographs (above) courtesy of the Free Library of Philadelphia.

Two pages from a Stewart-Warner instruction booklet with drawings and an explanation of how the “Vacuum Gasoline System” operates are via the MTFCA Forum.

17 responses to “Nothing New Under The Sun: Innovative Stewart-Warner Gasoline Feed by Vacuum

  1. Thanks for this. I had always understood the vacuum tank system to work more on a siphon action. I didn’t realize it was this sophisticated.

  2. Were these used or added as accessories in cars without a fuel pump? The 15 million model T Fords that were eventually on the road seem like a very strong opportunity for some aftermarket sales. All the stories come around to having to back your flivver up steeper grades because gas wouldn’t flow up to the motor from the fuel tank under the seat.

    • These were used as standard equipment on many cars and trucks other than Fords in the 1920s. The cars generally had their gas tanks hung on the rear frame cross member.

    • John,

      The lady’s hat is an interpretation based on a Chinese “Coolie” hat. Chinese fashion, furniture and culture were very popular and enjoying a renaissance at that time.

  3. I had one on my 1927 Chevy. Worked great after some cleanup. Early Chevys had them out of the factory.

    Henry did not use vacuum tanks and as far as I know, no Model T’s were retro fitted with one. Henry didn’t use them probably because it was an added complication and cost. Model T carburetors don’t like more than a few inches of pressure. Retro electric fuel pumps for Model T’s need a pressure reducer and are not as reliable as the gravity feed system. Except for very steep grades, backing up is not necessary if the tank if kept more than half full.

    • A few years ago, I had two bikes. The FZR 1000 had an electric fuel pump that died and left me stranded a couple of times. The FJ 1200 had a gravity-floww pump. Gravity never failed!!

  4. The Stewart Vacuum tank fuel delivery system is an incredible work of design! Almost Rube Goldberg in complexity, yet simple in operation, for about fifteen years, they were the single best way to solve fuel tank location and gasoline delivery to the engine. Gravity feed and pressurizing the gasoline tank by any of several methods all had drawbacks. Either inconvenience, or reliability under various conditions were a nuisance. While the Vacuum tank did have some drawbacks (especially at high elevations), it mostly worked well and reliably for many many years. It also had the advantage that if somehow the system did fail, one can fill the tank on the firewall (or some cars mounted it directly onto the engine) with over a quart of gasoline and continue on for a distance. Many people got home or to a repair shop with only minor inconvenience that way.

    While we can look at what came later and think the vacuum tank was a bizarre device compared to modern type fuel pumps, there really was no better solution in those years. While the diaphragm pump seems so obvious today, there was no material available in those earlier times that would do the job well and not fail often and early. Between the gasoline, certain contaminants, temperatures, and the constant mechanical motion and flexing, there just wasn’t any material suitable for mechanical diaphragm gasoline pump during those earlier years. The diaphragm fuel pump would have to wait until materials technology could catch up.
    By the mid ’20s, materials were being developed that began to make it possible for a diaphragm pump. It took a few years to prove their worth, however, by the early ’30s, the cheaper diaphragm pump became practical, and took over.

    I have had several antique cars with vacuum tanks. A little tinkering, and the vacuum tanks have worked well and I truly enjoyed the feel of technology as it was. I also always got a kick out of people amazed to see a vintage automobile that did not have an electric pump bypassing the vacuum tank! Yes, vacuum tanks have gotten a bit trickier after nearly a hundred yeas. Some of the valves inside have become loose from corrosion. Many of the flapper valves near the bottom tank have warped with age causing problems from sucking back. Also a lot of the steel tanks have rusted through in spots, but many of those can be repaired. And, however, a lot of those tanks were made way back when. And, for some reason, a lot more of the Stewart tanks have survived than the cars that need them have. Usually, looking through a few of the vacuum tanks can find good pieces and get one working well. And personally, I do like an antique automobile running on a vacuum tank!

    Also, they did indeed put vacuum tanks onto model Ts as after-market items. The coupe bodies in some years had the gasoline tank way back in the trunk. Those cars had more trouble in hills than most model Ts did have. I have seen a couple early T coupes with vacuum tanks installed way back when to help in hills. I also had a model T boat-tail speedster. It was an after-market body with the seat down on the floor, and the gasoline tank way in the back. I had a vacuum tank on it, and loved it that way.

    Thank you David G for another look at the automobile days of past.

    • My ’29 Hudson runs very happily on a vacuum tank and as a stop-gap measure I installed one on our ’14 Sunbeam ten years ago…

      Many cars of the immediate post-WW1 era built in the UK employ the Autovac system, which is essentially identical to Stewart-Warner. Some years ago I looked briefly to see where the system originated but I didn’t get a clear answer. My feeling is that there was some form of relationship between the companies.

      • I searched on the internet for “Patent Autovac Vacuum Petrol Feed Apparatus (Higginson, Arundel & Jay’s Patent)” and found a record from April 1927 of a court case in the UK in which Higginson and his colleagues won an extension to their pre-1910 patent of 18 months. Therein it is mentioned that the Stewart-Warner speedometer company was a licensee.
        It was claimed that the separate and later invention of Webb Jay was needed to make the Higginson and Arundel invention practical and this occurred in 1916.
        Joseph Higginson was a keen driver and his sensational winning ascent during the Shelsley Walsh hill-climb on 7 June 1913 established the brand new Vauxhall 30/98 as Britain’s must-have sports car for those with means – after a 4 year interruption for hostilities with Germany of course. It seems doubtful whether Vauxhalls used Autovacs before 1916. Also easy to find on the internet are Autovac’s instructions for keeping the system in good order. In France Weymann also took up Higginson’s patents and those with European cars of the period – e.g. Delage and Lancia – may be familiar with the Weymann “l’exhausteur” which is very similar.

  5. It appears that since the “mock-up” had a gas tank and radiator that it was functional and could be fired up to demonstrate the two devices.

  6. Next question for ole car bugs… my 22 T6 has this system. When sitting for 6 mths or more, was told to use “W” to prime system before starting. But, noticed a tiny brass funnel on the carb, which works easier.
    Question; was the small oiler can with spring holder in many engine compartments for extra gas for priming…?

  7. Priming the Stewart-Warner fuel pump through the “W” plug would do two things: It fed gasoline to the engine with a reserve to keep it running while the long gas lines filled up, and it allowed the mechanism to develop a vacuum between the pump and the fuel tank without robbing vacuum from the the engine supply side of the system.
    If starting your car for the first time of the season when everything is evaporated you could either crank your engine for a bit with the engine choked until the bowl filled up, or just prime the tank with a little funnel made of plumbing fittings and your engine will start of the first spark every time.

  8. I recommend reading the Stewart Vacuum manual. Under the section for “Care of the Stewart Gasoline System” it starts with bold letters: ” Leave Tank Alone. Don’t fool with it.”

    It is on the website about my old Marmon41, so I will check into how to submit it to this great site even though it isn’t actually a photograph.

  9. Thanks David for the interesting photo and easy to read diagram.
    Our 100 year old Series 4 Mercer still makes use of the Stewart Vacuum Tank System. The only problem we had was once with one of the valve seats coming ajar and that was on my way into the Hershey show field.

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