Vapor lock seems to be a leading cause of engine shutdowns for injected engines. How about a fuel system that CANNOT vapor lock, with an added feature that it can use most of the unusable fuel in a tank. Wouldn't that be nice?
Description: Use a nylon automotive screen at the tank pick-up. At entry to the fuselage from each tank, install a 3/8 inch fuel injection hose to a high-pressure electric fuel pump inlet. The outlet from each pump, 3/8 inch aluminum, routes to a TEE at the area of the fuel selector (which is no longer a fuel selector). 3/8 inch aluminum tubing routes forward to the firewall, connecting to the inlet of a LARGE size Andair Gascolator on the engine side. At the top side of the Gascolator is a 1/8 inch NPT tap that connects to a 1/4 inch aluminum tubing, immediately connected to a ball check valve (1/8 inch NPT fittings), connected to a fuel return line that terminates at the fuel selector valve, used to direct return fuel to either tank. The outlet of the Gascolator connects to the engine driven high pressure fuel pump. The outlet of that fuel pump connects to the fuel injector manifold. The ball check valve acts as an orifice to reduce fuel pressure from the electric pumps. A purist may want to install check valves around the fuel pumps that may allow fuel to easily be sucked in by the engine-driven fuel pump, but I found that it could suck fuel thru the engine-driven fuel pumps, so I did not do that. The positive sides of two fuel pumps are powered from two 10-amp fused (with resettable ATO fuses) circuits. The selection of a pump is from two redundant switches that connect the negative side of a fuel pump to turn it ON. These switches are the fuel selector. Note that it is possible to transfer fuel from one tank to the other. I installed a magnetic reed relay to sense the position of the return fuel selector, and this circuit activates a bright red LED on the panel immediately in front of the pilot when the selected pump is not returning to the same tank.
After I started flying with this system, I found a remakable, unintended feature: I could empty a tank down to less than two cups of remaining fuel. How this works: When the tank gets down to the last bit of fuel, the pump begins to suck a mixture of fuel and air, and the fuel pressure from the pump discharge begins to drop. The air/fuel mixture enters the Gascolator, and the air component immediately finds an exit and returns back to the tank. I found that the engine continued to run at full power with the injectors getting full pressure from the engine-driven fuel pump until the fuel pressure from the electric pump was below 10 PSI, at which time the fuel component of the air/fuel mixture was less than the fuel flow required by the engine. I immediately switched to the opposite tank and resumed full engine power.
Description: Use a nylon automotive screen at the tank pick-up. At entry to the fuselage from each tank, install a 3/8 inch fuel injection hose to a high-pressure electric fuel pump inlet. The outlet from each pump, 3/8 inch aluminum, routes to a TEE at the area of the fuel selector (which is no longer a fuel selector). 3/8 inch aluminum tubing routes forward to the firewall, connecting to the inlet of a LARGE size Andair Gascolator on the engine side. At the top side of the Gascolator is a 1/8 inch NPT tap that connects to a 1/4 inch aluminum tubing, immediately connected to a ball check valve (1/8 inch NPT fittings), connected to a fuel return line that terminates at the fuel selector valve, used to direct return fuel to either tank. The outlet of the Gascolator connects to the engine driven high pressure fuel pump. The outlet of that fuel pump connects to the fuel injector manifold. The ball check valve acts as an orifice to reduce fuel pressure from the electric pumps. A purist may want to install check valves around the fuel pumps that may allow fuel to easily be sucked in by the engine-driven fuel pump, but I found that it could suck fuel thru the engine-driven fuel pumps, so I did not do that. The positive sides of two fuel pumps are powered from two 10-amp fused (with resettable ATO fuses) circuits. The selection of a pump is from two redundant switches that connect the negative side of a fuel pump to turn it ON. These switches are the fuel selector. Note that it is possible to transfer fuel from one tank to the other. I installed a magnetic reed relay to sense the position of the return fuel selector, and this circuit activates a bright red LED on the panel immediately in front of the pilot when the selected pump is not returning to the same tank.
After I started flying with this system, I found a remakable, unintended feature: I could empty a tank down to less than two cups of remaining fuel. How this works: When the tank gets down to the last bit of fuel, the pump begins to suck a mixture of fuel and air, and the fuel pressure from the pump discharge begins to drop. The air/fuel mixture enters the Gascolator, and the air component immediately finds an exit and returns back to the tank. I found that the engine continued to run at full power with the injectors getting full pressure from the engine-driven fuel pump until the fuel pressure from the electric pump was below 10 PSI, at which time the fuel component of the air/fuel mixture was less than the fuel flow required by the engine. I immediately switched to the opposite tank and resumed full engine power.