MTFCA Forum

Any advice on plumbing in an air pump on the gas tank? I'm guessing I need to put in a relief valve to let off pressure. I've seen valves that will bleed off excess pressure at a pre determined limit, will these work? On the other end, if you're out in the sun and park the car in the garage it will create a negative pressure when it cools down. Is there anything out there that will let air in/out and keep the pressure from lets say 1-3 lbs? pressure

Pressure/vacuum fuel caps are availabe in a wide variety. I don't know of any that are adjustable. (EPA). I'd be very cautious about using any pressure/vacuum closure on a stock Model T tank, especially the ones that are more or less square and have flat panels. They were not designed to contain either pressure or vacuum. A pound or two of pressure probably would be OK, but much of any vacuum would likely collapse the tank to some degree. Temperature changes would cause pressure/vacuum situations even when the car was not running. I would expect a stock tank to develop cracks in short order, even if it didn't bulge or collapse. If you need a pressure system, a custom tank or one of the speedster style tanks would probably be the best route.

Don't know but found these https://www.zoro.com/ldi-industries-rel ... ifications

That will vent pressure, but apparently it does not have a vacuum relief function. Any relief device would be subject to failure, and might lead to serious issues.

Why do you want to pressurize your Model T gas tank?

There were period articles written about using a copper tube inserted into the exhaust pipe below the exhaust manifold and into the tank for pressure. The gasses are inert and a screen inline as a flame arrestor make it safe.

Pat, this is going on a speedster with the oval shaped tank. The carbs are too high to use the normal gravity system. There are a lot of speedsters out there with the pressurized system, someone has to know how they're set up.

This shouldn't be all that difficult? Are you using a hand pump? If so make sure it has a check valve on the end, some do, many do not (McMaster Carr). From the check valve go to a T fitting one end goes to your pressure gage (sometimes hard to find at the low pressures) the other end goes to your gas tank (fitting on the cap or some other arrangement). Pump it to 2-3 lbs. (I've never had much luck with pressure regulators) if it bleeds down you've got a leak. To relieve the pressure in the tank, open the gas tank cap (it's 2-3 lbs. of pressure). That's how my race car is plumbed and it works fine, the only issue I have is too much pressure (not paying attention) and the Winfield carburetor doesn't like it. Just my way of doing it, I'm sure there's others that work just as well if not better.

A 0-5 PSI gauge would be good. Typical gauges that go to 30 psi and up are nearly useless at very low pressures. A very small ball check, mounted upside down so that gravity would seat the ball, might work for a vacuum relief.

This is a simple set up, I have a speedster which has for the last 50 plus years had such a system. never fails.

hand pump connected to the neck of the fuel tank, connected by copper tube. with a low pressure gauge inserted. pump is in floor.
Pump up to 1 to 2 PSI. Sometimes if I drive a big distance I might have to get the wife to do a few more pumps especially if going up a steep hill. Usually on a sunny day the heat from the sun will keep it pressurized. Obviously the system has to be air tight and the pressure is let out by loosening off the gas cap.

I also have an exhaust pressure system as well , just a connection to the ex pipe through a expansion chamber to the pipe to the tank with a check valve to stop the hand pump air from going out the exhaust pipe. Its made out of normal plumbing pieces.