Ok let me see . . . the fuel comes from the tank into the lift pump on the outboard side of the IP.
From there it goes into the main fuel filter through a banjo bolt on the inboard side of the filter.
Just forward of that fuel filter inlet banjo bolt is the outlet banjo bolt that delivers fuel to the IP.
So the fuel enters the IP on the outboard side of the IP.
This outboard banjo bolt on the IP is the inlet to the fuel galley.
Now, on the INBOARD side of the IP is another Banjo bolt that has a second bolt head of a slightly smaller size. This is the fuel return to the tank through a junction on the top of the fuel filter. That inboard banjo bolt is the one I was referring to. That smaller bolt head is keeping a spring and ball assembly under compression and the ball acts like a check valve (a one-way valve). That check valve is what keeps a bit of pressure in the IP galley. If it isn't working properly, and depending how it fails, either air will not bleed out of the IP galley or there may not be the pressure needed to refill the individual pumps after each little squirt.
Now the injector return hoses are a different story. They are also pressurized by the lift pump, but only because the pressure pulse passes through to the return line through a small air bleed orifice at the top of the main filter. This keeps new air from getting into the injection pump once it has been bled of all air otherwise. And though it is a small hole it still lightly pressurizes the return lines of the injectors. I you are getting a lot of leaking through the injector return lines, then replacing those small hoses is indicated. And this may be where the relatively large amount of fuel in those return lines is coming from.
I know of no check valve to keep the return flow out of the injector return lines. Although installing one might not be a bad thing to try.
hope this helped.
Bogy.
"Hardware eventually fails. Software eventually works" - Michael Hartung
From: "Carl diyernh@comcast.net [diesel_mercedes]" <diesel_mercedes@yahoogroups.com>
To: diesel_mercedes@yahoogroups.com
Sent: Wednesday, August 17, 2016 7:18 PM
Subject: Re: [diesel_mercedes] loping engine
Sometimes it's small details.... Where is the "fuel galley return hose outlet check valve"? I'm seeing bad leaking on the injector return hoses. The injectors aren't supplying the quantity of fuel, it is coming from the fuel filter. Is there supposed to be a check valve to avoid the flow from the filter banjo bolt to injector overflow hose?
Thanks for the info.
Carl
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Posted by: Bogy Wan Kenobi <polespearbogy@yahoo.com>
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