Fuel pumps and filter

14 Aug 2005 Fuel pumps and filter

I’ve been trying to figure out the best place to install the fuel pumps and filters for several months. I had the following goals:
Maximize head pressure on the pump inlet
Minimize heat on the unpressurized sections of the fuel system
Minimize plumbing complexity
Install filters where it is easy to check and clean them
Have filters outside the cabin to avoid getting gasoline smell in the cabin when cleaning them
I didn’t achieve the last goal, and I only sort of achieved goal 4. I ended up installing the filters under the passenger seat, and the pumps under the rear baggage area. This will provide decent head pressure, particularly on the ground and during climb. During cruise, the head pressure will be OK, but not excellent. With the exception of installing a fuel pump wing pod, there are not many places on a low wing aircraft that provide a positive head pressure during cruise.

Here is a shot of the pumps installed. I’m missing one AN connector as you can see in the photo.

Here is a shot of the filters. In case you didn’t notice, I’ve taken these pictures at various stages of the installation. These filters are from Aeromotive, and have a 100 micron, reusable, stainless steel mesh filter. There is a very low pressure drop across these filters. You can see the high pressure line from the right pump comes under the two fuel pumps, and is connected to the other high pressure line with a T.

Here is a shot of the low pressure aluminum intake line, and the fuel injector hose high pressure line.

Here you can see the penetrations through the spar box. There are very few places on an RV8 where you can get something through the spar box.

Here you can see the Andair fuel valve, and the routing of the low pressure and high pressure lines.

Here is a closeup of some Federal Hose silicon tubing I used to protect the high pressure line from chafing on the floor center lip. This is right between the fuel filters. I’m not sure I’m 100% happy with this. Perhaps I’ll find a better way.

Here are a couple of shots of the pumps all wired up. This is the left pump.

This is the right pump. Notice the tygon tubing to route and protect the wires. The rudder cable is near there, and I don’t want any mishaps.

Overall I’m happy with the installation. I still need to do the fuel return line from the firewall to the fuel selector valve, and hook up the pressure sensors in front of the firewall. I’ll probably use the Andair bulkhead filter on the firewall, since that will provide some filtering, handle the firewall penetration, and allow me to transition the firewall with hose barbs on each side. There is no AN848-5 fitting, only -4 and -6. The fuel injection hose we use is 5/16s of an inch I.D. due to the sizes of the hose barbs on the fuel pumps.

I may still add a 10 micron filter after the Andair bulkhead filter, since this is what is used in cars. 70 micron seems a bit too coarse, but perhaps I’m being overly cautious.

Update: 2005-08-20

I changed the way I protect the hose under the fuel pumps. Here is the new method: