Walbro fuel pump disassembly

[joff]

Arizona Rotary Rockets donated a walbro fuel pump recently to me for destructive disassembly. The pump was out of a car that had experienced fuel system glitches. There actually didn't seem to be anything wrong with the pump, but Glen told me it will never go in a AZRR car because it can't be known for sure due to the circumstances in which it was replaced.

Anyway, some background on the pump before I post pictures.

The pump is covered under US patent #4500270 and the number is stamped right on the metal cover. http://www.freepatentsonline.com/4500270.pdf for full text of the patent. The patent includes many technical illustrations and detailed descriptions of the operation of the pump. The patent was published in 1985 and is now expired and free.

Abstract:
"A positive displacement fuel pump utilizing an in-line pump and armature with a flexible drive connection and spring-pressed backing plate for the pump and short cantilever mount shaft for the pump rotor."

This design is more similar to our oil pump (positive displacement) than our water pump (centrifugal). Or -- another way to look at it -- more similar to a twin-screw supercharger than a turbocharger.

There is a spring loaded one-way check valve in the plastic fuel outlet barb to keep pressure in the fuel system for faster starts. The check valve includes a very small spring and rubber gasket.

There is also a pressure relief valve that only allows maximum pressure to avoid hydro-locking the positive displacement gear pump. The pressure relief valve is a spring and rubber ball. The pump vents excess fuel to a port on the top of the pump.

The motor is a regular DC motor with spring loaded carbon brushes and commutator.

Size comparison with cell phone:
1.jpg

Bottom plastic piece removed -- gear rotor showing through opening
2.jpg

Metal cover removed
3.jpg

Top plastic piece and rubber o-ring
4.jpg

Top plastic piece pulled apart, showing brushes and brush springs
5.jpg