Came across this vid of a 24 Canuck touring, anybody know what the large canister on the firewall is all about..water injection?..Relevant part starts about 1:48.

https://www.youtube.com/watch?v=BkDURaRxy4U

Looks like an add on vacuum tank to get better fuel flow to the carburetor.

Looks like a vacuum tank.
Vacuum powered fuel pump.

Dennis types faster!

Stewart vacuum tank. Takes the place of a fuel pump.

Many, many brands of cars used them. Not the least of which were Dodge Brothers and Hudson-Essex.

I've never seen one, does engine vacuum pull more fuel than gravity, and if so why is this the first time I've ever seen one on a T?

The vacuum tank pulls gasoline from the fuel tank. The gasoline in the vacuum tank flows via gravity to the carburetor.

It operates via a vacuum line from the engine intake manifold. There is a float inside the vacuum tank and a valve mechanism so if fuel falls below a certain level, the vacuum tank refills itself. The vacuum tank cycles on and off.

Here is a good view of the vacuum tank on a 1927 Hupmobile that my dad owned. Note the line from the top of the vacuum tank to the intake, just above the carburetor.

Thanks Erik,..i learn something new here everyday. Is there a reason why you don't see more of this setup on T'S compared to other vehicles of the same time period?

Some random thoughts - Ford sensibly achieved gravity feed by having the benzene tank above the carburetor. I had a 490 chev that achieved gravity feed by dropping the carb below the tank via a long inlet manifold lol. I think chev went to vacuum tanks in the mid 20s before mechanical pumps arrived with the 6 cylinder cars. years ago at university I had a ford prefect that had vacuum powered windscreen wipers that were hopeless in the rain when ascending a steep hill.

My boat-tail has a vacuum tank because the gasoline tank is moved farther back in the chassis and fuel would not flow well on hills without some assistance. (My '24 coupe was from San Francisco and has a pressurized tank using a hand pump and a pressure gauge.)
I have seen other model Ts with vacuum tanks also. One was an early coupe with an era correct gasoline tank mounted at the back of the frame using a vacuum tank to pull the gasoline up to the front for the engine. Some Australian bodied Ts did that also.
While most Ts do fine with the gravity feed and the gasoline tank under the seat, there are quite a few Ts over the years that have had something done to help the fuel flow. In the late '10s through the late '20s, more non-Fords used vacuum tanks than did not. They were very common on everything else. Good ones usually work well and are fairly reliable under most common conditions.
I like having the one on my boat-tail.

They are a remarkable and somewhat complicated device. They use a lower chamber to store gasoline to gravity flow down to the carburetor. A smaller upper chamber is used to suck fuel from the gasoline tank using engine manifold vacuum controlled by a series of valves. Most of the valves are operated by a mechanical float inside the upper chamber. One valve is an anti-siphon gravity operated (flapper) valve.
Their biggest drawback is that when pulling a long hill. the engine vacuum can drop too low to pull the fuel up from the rear gasoline tank. That just when you need it most.
I personally like using them on cars that had them originally. Many antique car owners have been frightened away from using them, and put in electric pumps instead. This mostly due to simple fear of an unfamiliar and archaic technology. Like I said, good ones usually work very well. Usually a few simple repairs and they are good, as long as the tank chambers and float do not have any leaks in them.
Drive carefully, and enjoy, W2

Other than Ford I can't think of a car that didn't have a vacuum tank.
Buick, Chevrolet, Nash, Packard. Most cars had them.
I never could make one work that stopped working.
Many of them were made from cheap metal that corroded and cracked easily.
Some folks have installed electric fuel pumps inside of them just to make the car look original.

John,

You don't see more of them on T's because T's don't need them. When they work well they're an engineering marvel. When they act up they're a gift from Satan.

I have a troubled relationship with the one on my '24 Buick.

They drive on the left in northern Vermont? Who knew?

Another problem with the vacuum tanks is that many of the cars that had a vacuum tank also had pot metal carburetors. Over the years the zinc has leached out of the pot metal on many of those carbs and the remaining metal has lost its strength and will break unexpectedly. The bowl collapsing or the carb breaking off at the flange is common. Quite often a fire ensues. The vacuum tank is full of gas, feeding the fire. Some of them hold close to a quart of fuel, although most hold about a pint. That's a lot of gas feeding a fire with no way to shut it off. An electric pump can be shut off and a mechanical pump stops pumping fuel as soon as the engine stops turning. Virtually every T-1, T-2, U-1, U-2 Stromberg and most of the Zeniths of that era used on Chryslers, Hupmobiles, Franklins, Studebakers and many others have been replaced if the car they were on did not burn to the ground from a broken carb and a vacuum tank feeding the flames. I have on order right now two OX-2's, two OE-2's and one "anything that will work" carbs to replace pot metal versions of those carbs.

They are a genuine PIA to try to make work if they are worn. There are a couple different designs but basically they have two needles and seats, a float, a vacuum system with one or two check valves and it all has to be air and fuel tight.

When somebody calls me complaining that they can't adjust their carburetor that is just about my first question. 9 times out of 10 if they have a vacuum tank they have some kind of a bleed to the manifold that is pulling fuel from the vacuum tank directly instead of through the carb.

The little electric pump that Moss Motors sells for MGTC & TD replacement for less than 100 bucks will fit inside a tank, has low pressure without all the regulators and junk to try to make it work with early carb needles and seats and can be shut off so the fuel flow stops in case there is a fire.

I probably get a call a week from people wanting to know if I can rebuild their vacuum tank. The answer is no. I also don't work on pot metal carbs.

Stan, for the benefit of the curious, is it this pump?

http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=30838&SortOrder=10

Check out Airtex 8011E.

That's it Mark. I have had very good luck with those pumps. I've had one on an old tractor for years. I don't know if they are still available in 6 volt, tho.

The two biggest problems with vacuum fuel tanks, especially Stewart brand tanks, are the pot metal top and the fact that the brass tank itself was a deep-draw one piece stamping.

The process of deep drawing brass introduces much stress into the brass from this operation. It would have been simple to have annealed the brass after the stamping operation but, since they were operating trouble free for years, why add another operation to the process?

Now, some 80-90 years or more later, they are now cracking and leaking vacuum. They were never meant to last this long in the first place.

The other problem now inherent with these tanks, involves the die-cast pot metal top. As Mr. Howe stated above, unlike your grandmother, pot metal, Zamak, white metal, or whatever they call it out in your neck of the woods, does not age well.

There have been discussions on this forum regarding reasons for the deterioration of this material. I know someone that cleared out abandoned Dodge Brothers dealerships and found brand new, never used, still in the original box, die cast distributor bodies for four cylinder Dodges that had disintegrated in the box. This was in the early 70's.

My point is, vacuum and air leaks don't mix. If your car won't start and you have a vacuum tank, whether it be a G&G (Chevrolet) or Stewart, look there first.

If that is, in fact, your problem and you decide to install an electric fuel pump, try to install it in an inconspicuous place near the fuel tank. The reason for this is the fact that electric fuel pumps like to push, not pull. If you place the pump in the vacuum tank to hide the electric pump and the fuel tank is at the rear of the car with the pump on the firewall, you're looking for more trouble.

To retain the original look of the vacuum tank on the firewall, simply gut the vacuum tank and install a through pipe inside the tank.

Or, if you own a T, take it off and hang it on the wall in the garage next to the water pump.

John,

You don't see setups like this on Model T's because they are completely unnecessary. Adding complexity decreases reliability. This is one fine example of that. Adding fuel pumps or water pumps or ______ (fill in anything you want) is not going to add to the reliability of the T.

My dad never had a problem with the vacuum tank on his Hupmobile above. This was a low mileage, well kept unrestored car (only 10,000 miles) and everything ran smooth as silk.

I've never heard of the "long hill" problem either and never experienced it in all the years I rode with my dad in the Hupp. Even if the tank starts another draw cycle at the bottom of a hill, there is still plenty of gasoline already in the vacuum tank to handle any fuel requirement. In cars where it is a problem, perhaps the float isn't set right so too much fuel has emptied from the vacuum tank before another draw cycle starts.

Even the lowly American Rolls-Royce used the Stewart vacuum tank--but they fancied it up, at least on the outside. The reservoir tank is horizontal, and fits through the firewall, about 1/2 in and 1/2 out, the suction tank is the normal S/W unit and guts on a vertical can section mated to the horizontal tank. The top cover is a fancy brass piece with no markings on it at all to identify the maker (no pot-metal worries here). I would guess the reservoir tank probably has twice as much volume as the standard tank. And yes, it works wonderfully. Wish I could find my pics of it, but that was some 30 years ago! In one of my parts buys I have a NOS float, in the box (box is kinda sad).
Some say they are complicated, but I think rather simple and clever. The float activates a valve on the suction line; when it drops, it opens the suction line to the "pumping chamber (my name for it) and a fiber flap valve at the bottom of the chamber closes off the opening to the reservoir chamber. The suction pulls gas from the gas tank, and when it's full, the rising float trips the vacuum valve, shutting off the vacuum and opening the vent at the top. The fuel weight opens the flap valve and lets the fuel flow into the reservoir chamber. When the level of fuel in the pumping chamber drops low enough, the float throws the suction valve open, closes the vent valve, and starts the cycle again. The suction valve and vent valve are an "over-center" spring loaded bit so it's either wide open or shut tight. this is where things can go wrong; the springs fail, or the float fails is the usual problem.

I have been running a vacuum tank on my '25 TT for 30 years...a great addition for steep hills.

Erik,

Where sometimes a vacuum tank can be troublesome is in the situation that Stan describes, climbing a steep hill. Yes, the VT will just cycle more often, however, with the throttle most likely wide open, or nearly so, the vacuum pressure drops to a minimum and the tank takes longer to recycle. It's also got to raise the gas higher from the gas tank if the car is angled steeply uphill. Usually not a problem unless the VT has some reduced performance due to air leaks or other wear.

Since "nature abhors a vacuum" isn't the fuel actually pushed to the vacuumed area of the tank by atmospheric pressure, rather than pulled or sucked by the operation of the tank? Just asking because I have read that explanation somewhere.

I tried to copy my Dodge Brothers Stewart Vacuum Tank booklet. It shows the parts involved in one of these tanks ...

Tim E, Technically, that is correct.
Donnie B, Great booklet!
Thanks all.

Buicks used these too. I priced one to replace one I a 1922 Buick 20 years ago and they were 400 bucks