Fuel Delivery Problems?

[Msamsen]

I really doubt the manufacturer designed the fuel system to be drawn from the very bottom of the tank. Also find it hard to imagine an owner adding additional fuel ports to an existing tank. I'm pretty sure your setup is original.

Changing the draw from the top of the tank to the bottom may not solve the problem as the fuel system is still under vacuum. Prove your syphon tubes are still good in the process I outlined earlier, then connect the tank line and check for vacuum loss at the manifold. As both engines and the generator failed, commonality between the 3 ends at the manifold. Between the tank and the outlets in your manifold is likely the problem.

Ted

Wouldnt a pressure test provide the same result as a vacuum test?

 

[O C Diver]

Somethings leak under pressure that don't leak under vacuum. How are you going to pressure test the tank syphon tube?

Ted

 

[Msamsen]

Somethings leak under pressure that don't leak under vacuum. How are you going to pressure test the tank syphon tube?

Ted

The siphon tubes are copper tubing soldered into brass fittings. Barbed hose fitting with 1/2” hose and new SS clamps. It’s pretty tight but I’ll see if I can put the vacuum on it.

 

[O C Diver]

The siphon tubes are copper tubing soldered into brass fittings. Barbed hose fitting with 1/2” hose and new SS clamps. It’s pretty tight but I’ll see if I can put the vacuum on it.

Don't take it apart! Just put a new hose (with a clamp) on the existing hose barb and put the other items on the tee at the other end of the hose.

Ted

 

[TowLou]

Wouldnt a pressure test provide the same result as a vacuum test?

Ehhhhh no and yes? 10 psi is roughley equivalent to 20 inches of vacuum. You may have the same result or not. Since you see no fuel leak but a air intake leak you might need to add more pressure to get the fuel to leak. Air can expand a lot more then fluid in a controlled environment. Yes diesel does expand with a increase in temperature as well.

Check first any fitting you have touched a valve or filter then look at the whole system aftet that.

 

[Msamsen]

Ehhhhh no and yes? 10 psi is roughley equivalent to 20 inches of vacuum. You may have the same result or not. Since you see no fuel leak but a air intake leak you might need to add more pressure to get the fuel to leak. Air can expand a lot more then fluid in a controlled environment. Yes diesel does expand with a increase in temperature as well.

Check first any fitting you have touched a valve or filter then look at the whole system aftet that.

Ok will do. I’ve got the manifold under pressure as well as the line from the tank. I’m losing 5 psi on the gage every 15 minutes. No fuel leak detected yet, that I can see.

 

[TowLou]

Top of your raccor or a high fitting? Hows the o ring to the brass handle on top of the raccor or the cover o ring. Grab a bottle of soappy water and spray every fitting and all the lines you can see.

 

[Msamsen]

Top of your raccor or a high fitting? Hows the o ring to the brass handle on top of the raccor or the cover o ring. Grab a bottle of soappy water and spray every fitting and all the lines you can see.

I change those o rings out with every filter but ive also had them on and off a lot through this process. The soap and water test has not given me any bubbles yet. Im wondering if 20# pressure is enough?

 

[TowLou]

I change those o rings out with every filter but ive also had them on and off a lot through this process. The soap and water test has not given me any bubbles yet. Im wondering if 20# pressure is enough?

If you keep dropping air pressure it is more then enough.

 

[sunchaser]

Thanks for the info.
Just curious, do your engines pull the fuel up through a syphon hose or from the bottom tank fittings? Im thinking of switching mine back to the bottom as I think the siphon tubes are introducing air into the system causing eventual engine starvation.

What engine? Is the engine starving for fuel and shutting down? If so, is this a new happening that occurred after maintenance work or a filter change? Some clear tubing after the Racor will show air bubbles if they're present.

 

[Wayne]

Vacuum vs Pressure on Fuel Lines

On the Celestial, I had a fuel manifold somewhat like yours. The valves weaped fuel slowly and left a stain. I changed all the valves out with ball valves from a big box store and then had multiple air leaks under vacuum, but under pressure the valves were good. After extensive testing, I found that the new valves' stems leaked like a sieve under vacuum. Called Conbraco and asked if their Apollo valves were rated for vacuum as well as pressure (Data sheets at that time did not have any data about vacuum). I was assured that they would hold the vacuum that my system could generate. I replaced all of the valves with Apollo valves - problem permanently solved.

 

[Msamsen]

Hi Lepke,
I wanted to run a scenario by you to see what you think, since you are familiar with this system.
Ive now pressure tested the entire system and found no leaks.
But I have a theory on how the air might have gotten into the system.
When I first broke down, I checked the filters and both racors were dry down to the intake tube that leads to the engines and I wonder if that can happen due to the siphon tubes being emptied when the engine is off and not creating a vacuum for fuel to stay in.
Then every time I start the engines, air gets sucked into the top of the racor, creating more and more of a gap until it finally reaches the outflow tube to engines.

Here is a diagram of my system (if you can pull it up)
Bassically the tube sizes are 3/8" siphon to 1/2" fuel line to 3/8" coated hard line to Manifold and to racors then a big blue braided fuel line through the flow regs to engines.

 

[Msamsen]

On the Celestial, I had a fuel manifold somewhat like yours. The valves weaped fuel slowly and left a stain. I changed all the valves out with ball valves from a big box store and then had multiple air leaks under vacuum, but under pressure the valves were good. After extensive testing, I found that the new valves' stems leaked like a sieve under vacuum. Called Conbraco and asked if their Apollo valves were rated for vacuum as well as pressure (Data sheets at that time did not have any data about vacuum). I was assured that they would hold the vacuum that my system could generate. I replaced all of the valves with Apollo valves - problem permanently solved.

Thanks for the info. Mine look like original valves and manifold.
Just curious, what vacuum level did you test it at to find it leaked?

 

[Wayne]

vacuum

I really don't remember how much vacuum it could pull with the fuel tank valves closed, but it was whatever the fuel pump could pull. I installed the system much like Cap't Will's system that used a Walbro 6802 pump. I still have the diagram for the system. It was a perfect system for the boat, even though it had a manifold with multiple fuel valves on it (many folks don't like fuel manifolds). I never had any kind of problem with the fuel system that I installed. The trick was, I think, was that whenever the total fuel quantity went below half, I would pump all the fuel into one tank, and then pump it all back into the other tank, then open the cross-over valve to let the fuel levels equalize. That way all the fuel was run through the Racor filters at least once. I used 10 micron filters, although many recommended 20 micron filters. My neighbors, upon seeing the boat listing to one side, usually called to make sure it wasn't sinking. The boat had three tanks: 2 x 350 gal and a 60 gal day tank.