Fuel distribution panel allows air intrusion

[dieseljim]

My 2008 462 DD has two fuel distribution panels. Through trial and error, it was determined that the first panel is allowing air to enter the fuel flow and stop the engine. It doesn't leak fuel, but it allows air to enter. The second panel distributes fuel to the engine, generator and Webasto diesel heater. In order to use the boat, the first panel was bypassed by directly connecting the port tank to the second distribution panel. So now the fuel path is from the port tank to the second distribution panel which then routes it to a set of Racor filters prior going to the engine. Prior to bypassing the first panel, air bubbles were clearly visible in the Racor fuel bowls.

Anyone have experience rebuilding these distribution panels? They look to be pretty simple, just a box with valves. Attempting to loosen and tighten all the fittings at the panel had no effect on the air intrusion issue. Anyone see a valve itself fail and allow air in?


Thanks for any suggestions. Cheers.

[Comodave]

Welcome aboard. If the valve wasn’t sealed properly it could leak. Vibrations could loosen a connection. When I am doing connections like those I use Marine Tex as a sealant. It glues the fittings pretty much together permanently. So I make sure I put it together correctly the first time. No second chances. But I have never had a leak doing it that way. If I need to make a change I buy new valves, but if I planned correctly the first time I don’t need to make changes.

[mvweebles]

Agree with Comodave that first step is to reseal the fittings. My suggestion would be a high quality thread sealant. On the recommendation of Steve D'antonio, I've used LeakLock for diesel fittings for several years

Highside Leak Lock 4 0z Jar https://a.co/d/2Eh34VS

Peter

[twistedtree]

Also try snugging up the packing nuts around the valve stems.

[O C Diver]

I think you need to give us some more information. How many tanks do you have? What are the lines made of (copper tubing, hose, or) Have you determined it wasn't the line between the first and second panel that was leaking? Did you determine that air was leaking in regardless of which tank was being drawn from? Can you post a picture of the panel?

Ted

[sunchaser]

Questions
Is the leak around first panel or the feed line to the first panel?

What type of valves; gate or ball?

Does the feed line from the tank to first panel draw from same point as the “bypass” line?

[dieseljim]

Thanks for all the feedback. Attached are a couple of photos that show the manifold and the manifold's details. I have a port and starboard tank that feed into the shown manifold. Prior to bypassing this manifold, it didn't matter which tank was drawn from, air still entered the system. All the other valves on this manifold were also closed during this test, and still air got into the system.

In case you're interested in the manifold details. One of the outputs is labeled "auto suck". Why it's called that I don't know, but what it does is route fuel through a magnet and then to the upper distribution panel. Not sure I understand the purpose and haven't used it. The "pump" valves are for a polishing unit.

Given time constraints, I have had to ask the local boat yard to work through the issue for me. They anticipate pulling it off the boat and pressure testing it among other things. I'm looking forward to the days when I can do more on my own.

Cheers!

[dieseljim]

Second try on the photos

[O C Diver]

Well that's a mess.

My first observation is that there is a "return to port fuel tank". It would seem to me that if that valve were open, you might be sucking air out of that tank. Most returns dump into the top of the tank.

Ted

[Jeff F]

Originally Posted by dieseljim

In case you're interested in the manifold details. One of the outputs is labeled "auto suck". Why it's called that I don't know, but what it does is route fuel through a magnet and then to the upper distribution panel. Not sure I understand the purpose and haven't used it. The "pump" valves are for a polishing unit.

What do you mean by "upper distribution panel"?

I'm assuming that the manifold is partitioned between supply and return. If true and the pump circuit is closed the only fresh fuel is going to come through the "auto suck" port. Seems to me that this is the port that should feed the second panel.



Sent from my moto g play (2021) using Trawler Forum mobile app

[Nick F]

Originally Posted by O C Diver

My first observation is that there is a "return to port fuel tank". It would seem to me that if that valve were open, you might be sucking air out of that tank. Most returns dump into the top of the tank.

Ted

+ 1. Plug off this return and see if the problem goes away.

[fgarriso]

How many tanks do you have?

Do you return to the tank you are drawing from?
If not why?

Can you put fuel in all tanks and then try the running test again?

[O C Diver]

Originally Posted by dieseljim

Given time constraints, I have had to ask the local boat yard to work through the issue for me. They anticipate pulling it off the boat and pressure testing it among other things. I'm looking forward to the days when I can do more on my own.

Cheers!

This is one of those situations where you could spend more money trying to diagnose and repair a poorly designed system. The welded manifolds create a large number of failure points. Billet machined manifold blocks are far superior. A simple system of drawing from your 2 tanks and returning fuel to those tanks should look more like this.



Ted

[twistedtree]

Perhaps the OP could draw a schematic of the fuel system along with these various manifolds and valves. It's hard to offer advice without being certain what the situation is that leads to air intrusion, and what situation does not. Nor to offer possible ways to further diagnose and narrow down where the leak may be.


Note that pressure testing may not be sufficient, and in fact misleading. I have seen a number of situations where nothing leaks under pressure, but under vacuum they do. So if the manifolds are being removed and tested, they need to be vacuum tested as well as pressure tested.

[Tator]

Originally Posted by twistedtree

Perhaps the OP could draw a schematic of the fuel system along with these various manifolds and valves. It's hard to offer advice without being certain what the situation is that leads to air intrusion, and what situation does not. Nor to offer possible ways to further diagnose and narrow down where the leak may be.


Note that pressure testing may not be sufficient, and in fact misleading. I have seen a number of situations where nothing leaks under pressure, but under vacuum they do. So if the manifolds are being removed and tested, they need to be vacuum tested as well as pressure tested.

I am curious as to why something would pass a pressure test but not a vacuum test.

Tator

[O C Diver]

Originally Posted by Tator

I am curious as to why something would pass a pressure test but not a vacuum test.

Tator

Pressure can compress a seal or packaging by moving it in one direction. Vacuum can move that seal or packing in the other direction where it may not seal.

It's also easy to apply too much pressure to make a seal or packaging seal. Where as vacuum is a very small differential that may not force a seal or packing to move or tighten.

Ted

[Jeff F]

Originally Posted by O C Diver

A simple system of drawing from your 2 tanks and returning fuel to those tanks should look more like this.



Attachment 141010



Ted

Ted, I think the OP's manifold is two compartments. If you think of it that way it's set up much the same way as your pic and functionally equivalent.

I could be wrong, but it makes sense I think.

I'm guessing the OP didn't discover the valve combo to make it work. Hope they come back.

Sent from my moto g play (2021) using Trawler Forum mobile app

[O C Diver]

Originally Posted by Jeff F

Ted, I think the OP's manifold is two compartments. If you think of it that way it's set up much the same way as your pic and functionally equivalent.

I could be wrong, but it makes sense I think.

I'm guessing the OP didn't discover the valve combo to make it work. Hope they come back.

Sent from my moto g play (2021) using Trawler Forum mobile app

I can visualize that.

Ted

[dieseljim]

I'm finally back on the boat. It was determined that the "auto-suck" portion of the lower manifold was causing the air leaks. The routing of fuel through the magnet chambers has been cut-off and capped. So far, no air leaks after about 7 hours of operation. Thanks O C Driver for the explanation as to why I could have a vacuum leak but not a fuel leak.