I am in the midst of a speedster project which will have a new torpedo style gas tank. I have a Lunkenheimer pump which I plan on using to pressurize the tank. The pump has a valve to switch to exhaust for pressurizing with the exhaust gases. I know this was discussed sometime ago but cannot find the post. What I want to know is what are the hazards, where do you tap into the exhaust pipe and how much pressure could be expected using a 2" exhaust pipe without a muffler?
With 2" exhaust and no muffler you won't be able to build enough pressure to use it, Don.
That would scare the liver out of me. What if some fumes from the gas get into the exhaust system and it causes an explosion? Or what if the exhaust gas gets too hot and causes the gas to explode? You should be able to use a hand pump to get pressure or use a fuel pump.
No safety issues. The hot gasses are not actually traveling through the pipe (except at the gentle rate of, say, 3 gallons/hour to replace fuel used from the tank) and they will be ambient temperature when they arrive.
I had this arrangement for several years on my 1912 KisselKar, but changed to a hand pump for pressurization as it was difficult to get enough exhaust pressure to do the trick. My hand pump will build 3+ psi of pressure in the tank, but 0.5 psi is enough.
If you are going to try, tap the exhaust upstream of the muffler. The more restrictive the muffler, the better. As Don says, with no muffler, forget it.
Here is a previous thread on the subject:
I recently added an exhaust pressure system to my Fronty speedster. It has a hand pump and it only needs to be pressurized if the tank is below half full. The pump is on my left side in easy reach and the passenger can use it if they are in the car. RHD
Unfortunately my left shoulder is a bit messed up and it can be a pest pumping at times as that's the throttle side as well. So I decided on trying an exhaust pressure system before going to an electric pump which I did not want to use.
The speedster has a muffler so I drilled a hole before it about 2 ft from the motor. I connected a 1/4" pipe and connected a gauge. At idle there was only a flicker of the gauge but when the motor was sped up the gauge registered 2-3 pounds.
I them made a system up consisting of piping to an expansion chamber with a mesh filter and a NH carby valve. The valve lets the exhaust pressure through but prevents the pressure being lost back to the exhaust when I use the hand pump
The system works great. If I seal off the gas tank start up the motor the gauge just flickers, rev the motor and the pressure rises to around 2 psi.
Going up hills is when you need the pressure, the motor is under load so pressure is there. If you back off the pressure drops but you don't need it then.
As Chris said no safety issues, flames could not get to the gas to ignite it. Having a non return valve would help prevent fumes getting to the exhaust also. Using exhaust gas is one of the safe ways to weld gas tanks, by putting the exhaust into the tank the oxygen is expelled and the gas can't ignite, unfortunately like a lot of things the actual conditions present are different from those people assume are there.
Only time will tell if I end up with an explosion under my butt while driving the speedster I will just have to wait and see but I'm just about to give up on my copper fuel line fracturing from flexing as its been 49 years so far and the damn thing still hasn't broken.
Many cars of the Model T era had fuel tanks lower than the carburetor inlet. The period correct solution is to use a vacuum fuel pump. Like this:
How did you arrange the NH carb valve, Peter?
Is it upside down so it's closed by the weight of the valve when there's no exhaust pressure?
The vacuum tank for the firewall was used a lot pust ww1 through the 20's while exhaust pressure was used a lot in the pre teen era, like Chris 1912 Kissel Kar and a 1908 Benz i've seen. Both will work fine if properly designed and kept in order.
Simple gravity feed is of course the most reliable system, but sometimes it isn't practical to have the tank high enough..
Roger, yes I placed it upside down
I use an electric fuel pump on my speedster. All the pressure you need at the carburetor is about a half a pound. Fuel pressure from a foot tall tank is roughly 1/2 pound according to some old laws of Physics that I am remembering. (1/2 pound per foot of height)
With the carb higher than the tank, you have less chance of gas leaking out when the car is not running. You don't need to worry about a shutoff.
People do it, but since you asked about the hazards I will chime in. This is an old topic, and there are folks who swear to it being safe. You can extinguish a lit match in a bucket of gasoline too, but most people wouldn't try it or recommend it, seems intuitive to most. A common argument is that the exhaust gas is safe because it is inert. Yet we have postings every year asking why someone's muffler blew apart. I am attaching a picture Denis Delano posted recently of his muffler after a backfire and ask would you want that connected to your fuel tank?
The pump is not setup for exhaust gas pressure. If that were the case, you would need another line coming into the pump.
The pump has two positions as shown by the handle notations.
The one tagged HAND PUMP is for you to pump/pressurize the tank by hand.
The one tagged EXH.PRESS is probably vented to atmosphere for you to relieve the pressure in the system.
Hook it up to something and test it out.
Exploded mufflers are commonly the result of someone driving along and the ignition stops working momentarily (the switch gets bumped, the switch is intermittent, etc). So the car is rolling along pumping combustible mixture into the muffler. Then the ignition starts up again and BANG goes the muffler. A good working ignition switch will prevent almost all of these.
As Chris and Peter have described, no safety issues. I would not recommend for Jeff to try it though.
His pump has two ports on it. One port is for pumped air to the gas tank. The other port receives exhaust pressure. With the valve in one position, the hand pump is connected to the gas tank and the exh. pressure is isolated. In the other position, the hand pump is shut off and the exhaust pressure line is now connected to the line leading to the tank, (formerly connected with the hand pump).
Jerry is right, there has to be a way to close off the exhaust if you need to pressurize the tank while the engine is stopped (say on a hill) you add air so the gas can be forced to the carby once the motor has started you then have the exhaust to maintain the pressure.
As Roger noted this system was common on pre first world war cars, Dodge used it for a while. Its hard to find information on how it was done now but there is NO information on it ever being dangerous that I can find,
On the '10 Chalmers Detroit the pressure comes right off the back of the exhaust manifold. The manifold has a boss cast right into it at the rear of the manifold that is tapped for the line to the pump.
Opp's made a mistake, it was Buick not Dodge who used the system in the mid Teens. Thou they may have ???
Exhaust gas is inert, IF, the mixture is not too rich. I learned that the hard way when cutting an old anhydrous tank using an old truck exhaust for the "inert" gas. Turned out, the truck was running a bit rich, and charged the tank. Fortunately, the tank had several bungs that were open, and just "wheezed" for a few seconds. Lesson learned. Dave