VP44 cutaway and pictures

[tylerkck]

Just remember the pressure to open the overflow valve comes from the internal vane pump not the lift pump. QUOTE]

Looking at the pictures and flow diagrams, I think you're right. How did you come to this conclusion?

[edcasey]

When my VP44 died, I was amazed to find out I had to replace the pump with a rebuilt unit regardless of what was wrong. So a bad seal or ruptured diaphragm costs you the price of a rebuilt pump. I started researching the VP44 through several sources including Bosch literature, Bosch flow diagrams, talked twice to a rep from Bosch North America, talked to a few rebuilders and a local guy who has several VP44's in his garage he has disassembled (and modified). I've also spent much time on European website where many people repair rather than replace a radial-plunger distributor pump.

As you can see from the flow diagram, the vane-type supply pump pressurizes the fuel when it is spun by the driveshaft. As engine speed increases, pressure from the supply pump also increases. To keep the pump from developing too much pressure, a regulator valve is used. When the pump develops enough pressure to open the valve (15.2 psi if I remember correctly), some of the fuel is returned to the intake side of the vane pump through a return hole. The flow after the regulator valve is pretty easy to follow with some of the fuel being returned to the fuel tank through the overflow valve.