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Pierburg fuel pump diaphragm cut-off valve placement
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Charlo
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PostPosted: Sat Nov 03, 2018 6:35 pm    Post subject: Pierburg fuel pump diaphragm cut-off valve placement Reply with quote

Hello,
My question pertains to the Pierburg "Square Top" fuel pump on my '69 Beetle, and is regarding the replacement Diaphragm Cut-Off Valve (as it is called in the Bentley manual) from the Wolfsburg West 111198555 repair kit.
I've attached a pic showing the existing Valve, plus the new Valve from the kit.
The bottom side (as pictured) of this cut-off valve sets on/over a 1/4" outside dia. brass nub which is the top side of the pump upper half.
The issue is this: the new Valve is 1/4" inside dia., and will not set over the 1/4" outside dia. brass nub, even with a fair amount of force.
Whereas the old/existing Valve has a 5/16" inside dia., and fits over the 1/4" outside dia. nub perfectly.
Can you tell me how this cut-off valve should set on the nub ... i.e. is the one from the repair kit correct (and should be force-fit), or not? Wolfsburg West sent me another "correct" cut-off valve, but indeed was the same as the kit one.
Thank you forum!
Image may have been reduced in size. Click image to view fullscreen.

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67rustavenger
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PostPosted: Sat Nov 03, 2018 7:40 pm    Post subject: Re: Pierburg fuel pump diaphragm cut-off valve placement Reply with quote

The brass nub you speak of is actually 0.234" (5.95mm) in outside diameter.
The stock diaphragm cutoff fitting is 0.321" (8.15MM) in inside diameter.

How are you measuring the brass nub and the inside diameter if the diaphragm?

I installed a WW square top fuel pump rebuild kit last year. The pump has been preforming perfectly ever since.
The WW rebuild kits are pretty good and work well. You might want to re-check your measurements.

Good Luck.
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kreemoweet
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PostPosted: Sat Nov 03, 2018 9:10 pm    Post subject: Re: Pierburg fuel pump diaphragm cut-off valve placement Reply with quote

The issue I've seen with the WW rebuild kit cutoff diaphragms is that the little rubber disk that is supposed to
seal against the end of the 6 mm outlet pipe actually does no such thing because it is set too deep in the
'cup' part of the diaphragm and the cup bottoms out on the pump body before the seal contacts the outlet
pipe. This is easily tested just by blowing into the pump inlet (of a fully assembled pump). If the cutoff is working,
there will be no air flow, no matter how hard you blow. If there is, then it isn't. The WW rebuild kits I've seen
always failed that test. Under no circumstances should the cutoff valve be "forced" over the pipe, as the diaphragm
is operated by a very light spring.

There's nothing visibly wrong with the new cutoff valve pictured above, and it looks like it could be a corrected version
of the old bogus part that was in the kits. But, given the history of WW's terrible pump rebuild kits, it wouldn't surprise me
that there was some other screwup in the parts.
Perhaps WW will correct the issue (if there actually is one) in a decade or so if we all start complaining.
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baldessariclan
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PostPosted: Sun Nov 04, 2018 6:11 am    Post subject: Re: Pierburg fuel pump diaphragm cut-off valve placement Reply with quote

I had issues with the fuel cut-off valve diaphragm supplied in the Wolfsburg West rebuild kit as well. As mentioned by “kreemoweet” above, I discovered that the valve body seemed a bit too short, plus central rubber disc sat too deep for it to all work properly (see here for my original write-up on all this — https://www.thesamba.com/vw/forum/viewtopic.php?p=8798319&highlight=#8798319 ):

original/old part on left, new WW replacement part on right — central rubber disc (or “seal”) sits too deep on the new unit:

Image may have been reduced in size. Click image to view fullscreen.



Valve body extends a bit farther down on the original unit vs. new part:

Image may have been reduced in size. Click image to view fullscreen.



Image may have been reduced in size. Click image to view fullscreen.



Old valve assembly seemed to sit and seal correctly (unfortunately however, old diaphragm was too dried-out and stiff to reuse):

Image may have been reduced in size. Click image to view fullscreen.



On new part, had to press down very hard for inner gasket to seal, causing outer diaphragm to deform excessively. Internal spring not strong enough to make it seal / function correctly when reassembled.

Image may have been reduced in size. Click image to view fullscreen.


I ended up having to order and use a separate NOS component to make this part of pump function correctly:
https://www.vwnos.com/021-127-201

Anyway, sounds like the fuel cut-off valve / diaphragm part offered in Wolfsburg West’s latest fuel pump rebuild kits may still not work right either. — disappointing! Sad
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Charlo
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PostPosted: Sun Nov 04, 2018 12:32 pm    Post subject: Re: Pierburg fuel pump diaphragm cut-off valve placement Reply with quote

Thank you kindly to this Forum for your replies to my query!

My measurements are in agreement with what you stated, 67rustavenger...
I used an Empire brand brass inch/meter gauge that measures ID and OD to double-check.
So then..
The nub (or outlet pipe) measures 6mm OD. The ID of the WW diaphragm is 7 mm. That only leaves 1 mm difference, or .5 mm difference on the circumference. That's a 'force fit' IMHO (agreed, kreemoweet), making the WW diaphragm unusable. (However, apparently they've been 'upgraded' so the seal is not recessed and sets at the end of the outlet pipe).
So, I will use your link, baldessarician, for the NOS diaphragm. You must have found it to be larger than 7 mm ID WW part, and hopefully closer to the original 8.15 mm. ??

Thanks again fellow Sambians Smile
I"m well into my 3rd year of a body off restoration, and no way could I've done it so far without this forum, and good 'ol Bentley. (My first VW restro).
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kreemoweet
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PostPosted: Sun Nov 04, 2018 4:53 pm    Post subject: Re: Pierburg fuel pump diaphragm cut-off valve placement Reply with quote

Charlo wrote:
The nub (or outlet pipe) measures 6mm OD. The ID of the WW diaphragm is 7 mm. That only leaves 1 mm difference, or .5 mm difference on the circumference. That's a 'force fit' IMHO (agreed, kreemoweet), making the WW diaphragm unusable. (However, apparently they've been 'upgraded' so the seal is not recessed and sets at the end of the outlet pipe).


Could you explain that a little more, please? If there's .5 mm of clearance between the cutoff valve "can" ID and the output pipe OD, that is ample room for the valve to do
what it's supposed to. When the diaphragm is in place, the little sealing disk inside the "can" should be resting on top of the output pipe, or maybe it will need just a little
pressure (such as is provided by the small spring) to do so. It should be obvious by blowing into the pump discharge nipple whether it's being sealed off or not. The cutoff valve
only has a function when the pump is not operating. When the pump is operating, the fuel pressure is going to be holding the cutoff valve well away from the end of the little
output pipe we've been discussing.
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baldessariclan
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PostPosted: Mon Nov 05, 2018 8:13 am    Post subject: Re: Pierburg fuel pump diaphragm cut-off valve placement Reply with quote

Charlo wrote:
So, I will use your link, baldessarician, for the NOS diaphragm. You must have found it to be larger than 7 mm ID WW part, and hopefully closer to the original 8.15 mm. ??

Sorry, but I didn't bother to take any of the measurements you mentioned for the parts I used -- there weren't really any interference or sticking issues that I noticed between any of the components I tried. The new NOS fuel cut-off valve/diaphragm passed the "blowing" test described by kreemoweet, once everything was reassembled -- couldn't force any air back into or through the pump.

I did also play around a bit with modifying the WW fuel cut-off valve/diaphragm shown in my pictures, to see if I could make it work. I pulled out that center rubber disc, cut a couple more similar discs out of rubber washers, and then reinserted them all to help eliminate the gap in there. I additionally carefully deformed the metal surrounding disc (using socket around OD and bolt pressing under middle, in a vice) so it would sit lower, to help seal against the brass "nipple" in the fuel pump body. Got it to the point where it would at least partially seal, but still seemed to have some sort of a really tiny / slow leak that I couldn't completely eliminate. So finally just gave up and stuck with the NOS replacement part.
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Charlo
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PostPosted: Thu Nov 08, 2018 5:43 pm    Post subject: Re: Pierburg fuel pump diaphragm cut-off valve placement Reply with quote

Ok, success...
My pump, with the "updated" WW cut-off diaphragm, passed both of the blow tests - thx kreemoweet! - blowing into the pump outlet on the top portion, and into the pump inlet on the fully assembled pump.
Thx again to all of you - with your input and patience, I'm on the road to a rebuilt 'square top.' Smile
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