[Lynn]

The new Walbro FRx fuel pumps come in two flavors: in one, the fuel flows at all times that power is supplied to the pump. In the other type, the pump turns on when fuel is needed (back pressure falls below a preset.) This is also the behavior of the Carter rotary vane universal type fuel pumps.

This "on demand" behavior begs the question, "should some sort of flow control be incorporated into the swirl pot or should the pump be allowed to supply fuel continuously and the excess returned to the main tank in use?" (The return line is a given, so that aspect is not in question.) The advantages of the continuously running setup include simplicity and a dilution of the heat in fuel in main tanks. The disadvantage is that the pump runs continuously - making noise, using power and adding some finite amount of heat itself.

If one were going to have flow control, the question then becomes how to achieve it. One could use a pressure regulating valve on the return line, but I'd really rather not pressurize the whole system to control the fuel pump. So, a float valve of some sort seems to be the obvious solution. The $64K question is where does one find a suitable valve (or assembly) that lends itself to installation in a header tank? I have found some brass bodied float valves in the 3/8" size range, but these, as most I have found, are designed for flow control of water. The float material is the biggest potential problem with these (float arm length could also be a problem, but should be fairly easy to deal with.) retrofitting some tanks may also be an issue, but for the fuel cells with round, aviation style caps, it should not be an issue.

Thoughts and/or suggestions anyone?

Thanks,
Lynn