How did that firewall fuel/vacuum can work? Where can one be gotten?
I had one on a 28 Franklin. In a word, lousy.
The principle is simple. Picture a toilet tank with the lid sealed. Engine vacuum applied to the tank sucks fuel out of the fuel tank until a float stops the vacuum. The fuel flows by gravity to the carb. The problem is when you're driving with an open throttle, steady state down the paved highway, there is little vacuum running to the tank and you run out of gas for a while. An electric fuel pump is usually hidden somewhere on the frame of cars equipped with these tanks nowadays.
GM cars of the 20's had these vacuum-operated fuel pumps. I know the '25 Buick had one.
If you have a battery, even a six volt battery, I'd run a 12v pump instead of having a pint of fuel sitting on my firewall. The 12v pump will work just fine on 6v.
When I was growing up, my dad owned a 1927 Hupmobile with a vacuum tank system. Never experienced any fuel starvation problems as described by Thomas Miller.
They actually worked great. I had one on a 27' Chevy Landau Coupe. They used engine vacuum to pull the gas into the firewall reservoir from the tank and then it was gravity feed from the tank to the carb. Inside there was a float and needle valve that would shut off the vacuum or fuel supply (can't remember which) when the tank got full.
When they are in good shape they seem to work really well. Dad had one on his '28 Chevy and it worked fine.
This thread may be a result of a previous posting where I show a tank installation....
The use of the vacuum tank has been trouble free and supplies a consistent fuel supply in steep terrains that I experience. The only problem with it is that it needs to be primed/filled if it evaporates or loses content through inactivity.
My 1930 Plymouth has a vacuum tank and it works just fine. You just have to set them up right and make sure they are free of leaks. Plymouth changed over to diaphragm pumps early in the 1930 model year but they actually turned out to be less reliable than the vacuum tanks as they were prone to diaphragm failure.
I removed a unreliable electric fuel pump on a 30 Dodge and replaced it with a vacuum tank. It would draw fuel with the choke on while cranking the engine over with a starter after sitting for months.
aproperly working vacuum tank is quite reliable and I prefer them to an electric fuel pump.
I've seen an electric pump hidden inside one of these tanks...
I still prefer gravity!
I once owned a 6 cylinder 1915 Jeffery automobile which had a factory equipped vacuum can fuel pump.
The fuel tank was low down in the rear if the car.
There was a little venture located between the carburetor and the intake manifold which supplied boosted vacuum to the pump.
This pump worked flawlessly the entire time I owned the car.
Eventually one of the superior mechanics (more recent owner) decided to spiff it up with carburetor cleaner which dissolved the little phenolic flap valve at the bottom of the inner tank whereupon it never pumped again. As I recall the valve assembly could not be removed without unsoldering the whole can assembly.
Just a word of caution
These tanks are really just an extension of the Henry Ford philosophy of KISS. They use manifold vacuum to draw fuel from a low spot and feed it by gravity to the carb mounted down low on the motor. They are extremely reliable.
As mentioned previously, they can need a prime if allowed to dry out completely by 6 months or a year of sitting or if the fuel tank is empty.
I have often wondered at the change over to the mechanical pumps which are a good deal less reliable and cannot only fail but mix gas in with the oil inside of a motor. The tanks were probably more costly to make but the big reason for the switch may have been the switch from updraft to downdraft carbies. A tank can't force fuel uphill!
I have converted both of my Hudsons back to tanks from modern electric pumps. There were no issues at all, I wish I had done it years ago. The picture below shows the Hudsons are the Muckenthaler Cultural Center in Fullerton yesterday at the 1920s Christmas Open House. The Model T had to stay home as I couldn't find a driver for it on short notice. It would have been a great dat for it too as the temp ran to the mid seventies.