Do I need a "check valve" on my fuel pump when . . .

[Gogar]

I recently bought a Walbro fuel pump to replace the bad CIS pump in my Targa. (its a 72 but has a 73.5 CIS motor.)

As many of you know, the fuel pump in those years is located in the Drivers rear wheelwell area, intstead of the front crossmember like later CIS cars.

I'm having a VERY difficult time finding a fitting for the output side of the Walbro that includes a check valve, or an adapter that will allow me to use the check valve that was on my previous Bosch pump.

Which makes me wonder:

How necessary is the fuel pump check valve when the pump is located SO MUCH closer to the accumulator? (about 18 inches.) Am I correct in thinking that the accumulator and the FP check valve perform similar functions?

It would be really easy to just use the barbed fittings that came with the Walbro and not worry about it. But I'll go ahead and worry about it right now.

If you have a Walbro, as I think many of you do, Where/How/Why/Why not did you do about the check valve?

Thanks!

[Gogar]

Also, if anyone knows the thread size of the Walbro stuff, let me know? I'm not near it right now.

Thanks

[coolngroovy]

I am not familiar with the Walbro pump, but when i was sourcing a check valve for my '74 CIS they were NLA.
I placed a wanted add on these forums, & a nice friendly man sold me a n.o.s check valve. He was even kind enough to send it to Oz!

I think the purpose of the cv is to stop the return flow of fuel back to the tank when the engine is turned off.

If it is not fitted, then the engine will require additional cranking to pump the fuel system pressure back up.

That's my understanding.

Cheers, Col.

[Gogar]

You can actually buy a VW CIS check valve that is identical to the Porsche part, AFAIK.

I understand the check valve concept, and I understand that the accumulator accomplishes the same task in a different location. I"m just musing whether or not a check valve is "as necessary" when the fuel pump is in it's '72-'73 location, in the rear of the car, when it's about 5 feet closer to the accumulator. It seems to me that all the check valve would do is keep fuel in that 2-foot section of hose between the pump and the Accumulator Maybe that's important, I guess.

[ossiblue]

Don't know about the Walbro pump but some aftermarket pumps have a built-in check valve. The Bosch pump was replaced in my 73.5T with a new pump (sorry, don't know the mfg.) and repositioned in the front as in later cars. The new pump has an internal check valve. Someone with a Walbro should respond with confirmation on integral check valves.

[my1st911]

Originally Posted by Gogar

You can actually buy a VW CIS check valve that is identical to the Porsche part, AFAIK.

I understand the check valve concept, and I understand that the accumulator accomplishes the same task in a different location. I"m just musing whether or not a check valve is "as necessary" when the fuel pump is in it's '72-'73 location, in the rear of the car, when it's about 5 feet closer to the accumulator. It seems to me that all the check valve would do is keep fuel in that 2-foot section of hose between the pump and the Accumulator Maybe that's important, I guess.

Both the check valve and accumulator do not do the same thing. The check valve is needed. When the car is shut off, the pressure from the pump stops, and the valve closes. Since it closes, it maintains the pressure. After a while pressure will bleed off normally, just by temperature fluctuations, and other minor factors. This pressure bleed off although usually small will be combated by the accumulator which is a spring type diaphram that pushes on the fuel and keeps pressure up. In terms of a walbro pump, I dont know. I believe most people here would have used a bosch or even peirburg. Slight modification might be required, but it has the check valve, and pretty cut and dry. If I'm wrong, I'm sure someone will correct me and give me a wedgie

[Gogar]

So, the check valve keeps the pressure up, and the accumulator . . . keeps the pressure up.

[mspirito]

You need the check valve because without it the car will be nearly impossible to start when hot.
I had the hot start problem and it was cured with the check valve.
Mike

[ischmitz]

The check valve prevents vapor from building up when the engine is shut down. Without it the fuel literaly will start to boil in th fuel rails from the heat soak of the engine block. It will cause hot-start issues. It acts like a diode (flow in onde direction but not in the other) in an electronic circuit.

The accumulator is to smooth and dampen the fuel pressure spikes during engine operation caused from the injectors. It is a storage device that acts like a capacitor or small battery in an electronic circuit.

Ingo

[Gogar]

Just FYI everybody, I emailed Walbro and they confirmed that their inline fuel pumps have an integrated check valve, so I was worrying about a lot for no reason. Also fellow Pelican Jim Sims, who has a lot of experience with these pumps, agreed on the internal check valve.

It never hurts to discuss first anyway!