Better schematic from eBay.

It's seal 111

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David


1996 Mercedes S124 E300TD - 129k - rolling restoration project -

1998 Mercedes W210 300TD - 118k (assimilated into above vehicle)

Got it! Two peoples separated by a common language...

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Nice diagram for injection pump, what engine & year if you know?

I'm searching internet for return flow info, leaks, bubbles, etc... found another interesting article from Parker Hannifin Corporation:

The phenomena of air in diesel fuel... pdf

https://www.google.com/search?q=The+phenomenon+of+air+separation+in+diesel+fuel&oq=The+phenomenon+of+air+separation+in+diesel+fuel&aqs=chrome..69i57.22903j0j7&sourceid=chrome&ie=UTF-8

Would someone clarify why the return fuel flow is connected to the top of the filter housing. Is it to provide an escape path for air captured in the top of the filter? If so the Parker article seems to indicate there should be a small orifice at that connection point. I found one other reference to the use of a small orifice to separate air & fuel on one of the bio-diesel sites.

Has anyone used Permatex 82099 on their vehicles. I'm wondering if it would help protect rubber bushings & other components from ozone damage.
I've sent off a question to them about resistance to diesel but I'm guessing diesel will soften it since it is a solvent.

There's an impressive amount of overthinking happening in this thread. When YOUR vehicle has air ingress problems and other people's don't, it isn't a design of the engine or fuel system, it's a problem with your vehicle - O-rings and fittings usually.

The connection of the return line on the filter housing is common for most of the diesels. There is a TINY orifice in there to allow the filter to bleed air out. If it wasn't there, you'd fill the filter with air for any leak upstream of the lift pump.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

There is an orifice there, its about 0.7 or 0.8mm in size.

By the design of the plumbing its to pull air out of the filter.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

This is a picture of the later type of Fuel Pressure Relief/Overflow Valve. I don't know if they all look the same inside or not but people have said the plastic part has issues when it gets older.
The design is supposed to allow the air to bled out.

On my 84 300D the Fuel Pressure Relief/Overflow Valve has only the ball bearing and a spring inside. However, it is not disigned to easily bleed the air out which is why the Fuel Supply/Lift Pump has a hand primer on it.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel