fuel pressure regulator...am i missing a part ?

[Dave H]

Have i got a part missing in my fuel pressure regulator ? during the strip down of this part i might of lost an internal part.
In an exploded picture it shows a small dowel shaped object that fits one side or the other of the diaphragm and spring.
This makes sense as it would allow the diaphragm to seal on something and act as a valve.
At the moment, when it is assembled ,the diaphragm with the assistance of the spring behind it does not touch the valve seat in the alloy casting.
Its about 5mm short of makeing a seal so the regulator would be open all of the time and allow fuel to return to the tank at any pressure.
 

[Dave H]

The part i think i might be missing is A1863000274 and its description is, "plug" fuel pressure damper.
The only detail i can find on this part is from an exploded drawing on the SLS website showing the internal parts of the regulator.
I am guessing the regulator works in the closed position but as fuel pressure increases it pushes on the diaphragm and its spring and lifts it off its seat allowing
excess fuel to return to the tank.
My problem is that the diaphragm, with the spring pushing on it, does not stretch enough towards the valve seat to act as a closed valve so i guess something is missing ?
Is it suposed to be open all of the time ? if so what is the purpose of the regulator ?
 

[Tomnistuff]

I just went into the garage and assembled mine (awaiting some CAD plated screws), and found that, like yours, it does not close off with the spring pressure.  Mine has the plug and no parts are missing.  I did find, however, that since mine has been sitting several months dry and the diaphragm is 47 years old, the diaphragm is very stiff.  I think I will replace the diaphragm before reassembling it for the restoration.  When I say, "stiff", I mean, "STIFF", almost like cardboard.

The stiffness of the diaphragm on mine is definitely enough to keep the spring from deflecting it onto the seat at the inlet.  If the diaphragm is supposed to be supple like a typical carburetor accelerator pump diaphragm, then mine MUST be replaced.  So, I really appreciate your post.  I would not have known of the problem.

Tom Kizer

[wwheeler]

I have rebuilt two of these and never remember seeing a plug. Mine was from a '68 W111, so maybe that is a difference. I only replaced the spring and diaphragm and the many seal rings on the fittings. They always worked just fine after rebuild which only done to clean things up.

The only tricky part is seating the spring when assembling so that the diaphragm isn't distorted around the sealing face. I used a rod through the open end to push on the spring and diaphragm so that it is aligned with the casting face. Then tighten bolts.

Yes the diaphragm should be soft and pliable. Just like a carb diaphragm.

[Tomnistuff]

The "plug" is just a pin with a rounded upper end that is apparently pressed into the rear housing and sits inside the spring.  It apparently acts as a diaphragm "stop" in the event there is an over-pressure situation.  It's logical to me, since when the diaphragm moves away from its seat a certain distance, the flow area is no longer controlled by the diaphragm travel but is controlled by the diameter of the inlet, so to avoid damaging the diaphragm due to over-travel, there is a "stop".  I suppose they vary in length depending on model and that is why it is a separate press-in piece.

Tom Kizer

[ja17]

Don't think it is a regulator, just a fuel noise dampner.

[Dave H]

Thank you for your replys, i have the stop part you mentioned pressed into the rear cover as you said and it would stop the excess travel of the diaphragm.
This part it seems acts more like a pulsation dampener than any relief/overpessure valve.
This would make sense as the diaphragm would have to be made out of elastic to travel far enough forward if it were to act as a valve.
I now know i have no parts missing, i will order a new diaphragm while i have it apart as they are only euro 30.

[Tomnistuff]

I hadn`t considered the idea of a noise or pulsation damper, but since the diaphragm isn`t large enough to travel far enough to block the inlet, that must be its function.  The injection pump would most certainly create a sort of "water-hammer" effect, so it's logical to avoid setting up noisy shock waves in the return line.
Wow, we live and learn, if we listen.  Reverse engineering is not as easy as forward engineering.
Thanks for the insight.
Tom Kizer

[travellerdogs]

Just noticed the questions on the fuel damper. It is not a fuel regulator. I went through the same query a while back. I am rebuilding mine after finally getting the new diaphram. There is no plug on mine either. Just a spring that registers on that little dimple in the bakelite part and the other end of the spring sits in the cup on the rubber diaphram. when the two parts are bolted together the rubber diaphram creates a seal between the alloy surface and the raised portion of the bakelite part. That holds the diaphram in place. The diaphram then just absorbs the pulses in the return line from the IP. That is my understanding of this part. I just have to insert a small rod of bolt in the end of the fitting to hold the diaphram from being pushed down too far in the alloy portion as this would wrinkle the rubber edge so that when it is bolted together there would be no seal between the two parts. Think of this as a rubber membrane that flexes with the fuel pulses.

[Tomnistuff]

Travellerdogs,
After reading your post a few times, I have drawn a couple of conclusions.  I agree with all you say.  It`s the same thing, said a different way, as in my last post.  The major difference is, apparently, that of all the posts, my car is the earliest.  My late 230SL damper assembly is all die-cast aluminum, including the spring side of the housing.  There is no bakelite.  I suppose MB concluded that the"plug" isn't necessary to keep from overpressuring the diaphragm by limiting its travel and that Bakelite is adequate to contain the spring and seal the diaphragm.  I am now curious.  I think I will look at the EPC and see when they changed the part number of the spring side of the housing and when they deleted the "plug".  I suspect they changed to Bakelite at the same time as they deleted the "plug".

Tom Kizer

[escapee]

Hi guys, I need to rebuild my fuel pressure regulator too. Can anyone kindly point out to me where can I get the diaphragm, spring and plug? I tried at SLS but it shows no stock. 

[wwheeler]

SLS won't have stock because it is a Mercedes factory part. They have been restricted for awhile now. You will have to buy directly from a Mercedes dealer or either Classic Center. Not sure if it is still available. 

[escapee]

Alright, shall check with my local authorised dealer. But I need the part no for the diaphragm, couldn't find it anywhere.

Understand that the part no. for the Pressure Spring is A1279930001 and the Plug is A1863000274. Correct me if i got it wrong.

thanks in advance. 

[wwheeler]

#127 070 00 52 is what I used on my W111. Should be the same.