This session was devoted to finishing up some firewall forward tasks—specifically the mechanical fuel pump drain and the appropriately named sniffle valve. The fuel pump drain is designed to provide an outlet for fuel in the event of an internal failure, so it is important to have it routed away from any heat source. The pictures show the path of the line from the pump to an exit point away from the cowling and exhaust. The line itself is connected to a fitting at the pump, and to a small length of aluminum tubing that provides some rigidity as it connects to the engine mount and then exits through a hole in the bottom of the fuselage.
The sniffle valve is designed to allow any residual fuel in the injection system to drain after engine shut down. My understanding is that while it is not uncommon to have a small amount of fuel draining, there are many engines that rarely, if ever, have fuel drain from this location. The valve itself is made of brass with a 1/8” NPT that threads into the bottom of the engine in a location where the air is distributed to the four cylinders. There were a couple of ounces of preservative oil that drained from the engine when I removed the plug, and once cleaned up, I put some thread sealant on the fitting and tightened the assembly in the case. A short length of fuel hose, a couple of hose clamps, and about 18” of 3/8” aluminum tubing completed the job. The aft portion is secured to the nose gear mount and is vented between the exhaust pipes.
