Subject: [FlyRotary] Fuel Delivery - Vapor Lock

First, it appears that at least one of the incidents resulted from the = fuel pumps/gas collator/lines getting hot enough to cause vapor lock at the = inlet of the pump(s). The a/c was running mogas at the time of the engine stoppage. One solution appears to be to shield and cool the pumps = and related plumbing with fresh air.

Once this happened, it led to the second shortcoming (I have experienced = this with my 20B installation during ground runs). Once the system had = vapor downstream of the pump(s), the efi pump couldn't force it past the = pressure regulator. This can be the result of either vapor lock or running = a tank dry. Their recommendation here is to install a bleed orifice = (approx. .020") around the pressure regulator.

Now, the Subie guys are contemplating a re-design of their fuel = systems. I'm wondering now if I should make any changes to my fuel system (2 wing = tanks, 6-port Andair valve, dual EFI pumps mounted on f/w)? Comments = would be welcome, especially from those that have been flying for a while.

Mark S.

Clearly this is an important = issue and warrants critical review in anyone’s plane. It seemed to me = there are some basic considerations; somewhat dictated by the airplane = design. I haven’t been flying yet but my thoughts on designing the system = incorporate these;

Minimize the = potential for pressure drop upstream of the pump. If you are pumping from a = sump tank, don’t pump off the bottom, and have a sump drain there = to take care of any water, and have a relatively coarse screen at the exit = from the main tank to take out anything that you don’t want going = through the pump. Skip the gascolator upstream. Put your 10-30 micron = filter downstream from the pump.
Have the pump at a = low point; i.e., in a position of always having positive pressure, maybe a = foot or two of head if possible, and where any air or vapor bubble will = migrate back toward the tank when the flow is stopped. If there is = fuel at the inlet or in the pump there is no problem having it force any = air or vapor downstream through the pressure regulator. Don’t expect = the pump to ever have to “suck” the fuel = uphill.
Have the pumps and = filter in a relatively cool place. I don’t particularly like = having fuel in the cabin, but at the bottom of the firewall is a = “cool” place, and some airflow over them couldn’t = hurt.

Hopefully this will keep me from = having any problems. We’ll see.