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Old 09-24-2020, 09:36 AM   #41
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With each engine drawing and returning to the separate tanks, how could return flow occur preferentially to the starboard tank? Are you certain that the "off" valves are not in the "on" position. It may be possible for valve handles can be put on backwards. I agree with others that crossover should not be the problem, especially if closed. We always kept it closed to avoid unbalanced fuel tanks when underway. Best to level tanks off when stationary and boat is relatively trimmed. At least in theory, a vessel out of trim, can result in fuel flowing preferentially to the lower side if crossover is open.
Thanks for the response. After all this head-scratching and the response from the members, it really has me thinking that one of my valves has to be backwards. Considering, my generator pulls from the starboard tank and returns to Port but my starboard tank is definitely being filled while underway. Also, I should be able to have my crossover tank open while underway so the tanks remain balanced for stability purposes. I was under the assumption that if one valve is closed the crossover, should not transfer. After docking, I open both crossover valves and the tanks balance out overnight. Then, I close both crossover valves and get underway and my starboard tank begins to offset.

The first item to address is replacing those valves so that I can Ensure they both are closed. Then, I'm going to put a couple vacuum gauges on my fuel draw lines.
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Old 09-24-2020, 09:59 AM   #42
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If you are running 3208's at mid speed you should consume 5gph ea or ~30 gal total in 3 hours. Sounds like you are drawing from one tank and returning to both. The dia of the supply line may not be large enough to supply both engines simultaneously at X speed.

You should check check each valve in the manifold. A stem may have snapped. I would also blow out the supply line with compressed air. I would remove any screens from the vents. They can oxidize and reduce air flow.
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Old 09-24-2020, 10:10 AM   #43
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Vents were my first thought, but I stared at the schematic and re-read the OP a couple times, and I had to wonder - the problem shows up when the cross-overs are open. I would expect the vents would be an issue with the cross-overs closed. Then the OP stated he filled-up and found one tank way-down, the other over-filled. I have to wonder if there is some sort of contention with the manifold - maybe it's mounted low, not sure if the draws are bottom-tank or top-tank. But it's not a brand new boat so something changed. Manifold has been there a long time.....hmmm...

I like the idea of a crossover with a reversible pump to manually balance when needed (but run closed). Groco makes a 6-port valve that's made to select between two tanks on a single engine - it switches supply and return with a single turn of the handle. One valve per engine (three total, including generator) and you have 100% control of both feed and return. But I have to say, it's a lot of work and money so would definitely figure out the smoking-gun problem. This one is odd....

Good luck, and thanks for sharing.

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Old 09-24-2020, 10:32 AM   #44
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Thanks much for the detailed response and valuable input. I think you are right on the money. Since I have closed both crossover valves, I've had zero issues.

However, I nearly topped off both tanks yesterday and made a three-hour run. When I returned to the dock to check my fuel levels, my port tank was down 40 gallons and my starboard was nearly over filled. I think the vacuum gauges will be a Telltale of what's really going on.

I also agree on the gate valves as those are on my list of swapping out as well.
It seems your problems and solution(s) are getting clearer. Fuel flow 101 needs further analysis and you're getting there. Don't forget about a return manifold so you can be 100% sure you're returning to the tank you're drawing from.

As discussed, get those valves handles setup right. Don't guess, remove the fuel line from the valve and check for correct open/close. Mark each valve as to location to and from. While you're at it, put some calibration marks on the sight tubes.
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Old 09-24-2020, 11:27 AM   #45
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I am VERY familiar with the Jefferson fuel system and consider it a very poorly thought out system, especially that ridiculous "manifold" cylinder where all fuel users encounter a common point. The other hateful thing in your system in the standpipe draw which can allow you to lose fuel prime to the Racors by making one wrong valve setting when opening any one of the Racors.

RIP IT ALL OUT.

Replace both inappropriate tank crossover valves with tees with two ball valves attached, one pair of valves (BOTH normally closed) reconnecting the crossover line and the other pair connecting to the main engine Racors. Downstream of the Racors you can run another cross-connect line with a single ball valve (normally shut) which will enable you to run both engines off one Racor while you quickly open the other to change a clogged filter element. Believe me, it can be done.

A VERY important element in this system would be an electric priming pump with a bypass valve arrangement. I can send a diagram of this highly flexible and successful system I installed in my twin GB42 to your PM if you like.
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Old 09-24-2020, 11:46 AM   #46
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Originally Posted by SoWhat View Post
If you are running 3208's at mid speed you should consume 5gph ea or ~30 gal total in 3 hours. Sounds like you are drawing from one tank and returning to both. The dia of the supply line may not be large enough to supply both engines simultaneously at X speed.

You should check check each valve in the manifold. A stem may have snapped. I would also blow out the supply line with compressed air. I would remove any screens from the vents. They can oxidize and reduce air flow.

Thanks for the input...I'm going to check my manifold this evening and remove my supply line(s) and ensure they are clear as you suggested. My estimate for fuel burn is exactly what you stated. I love my T3208's as she seems to be a sipper for her weight/crusing speed ratio. My wife is actually super impressed as the starboard fuel tank seems to be making fuel, lol.

Seriously, I do know that each engine returns to its respective tank as the return leaves the top of the main and goes directly into that tank. I have no return manifold. How it could be transferring is mind-boggling unless the transfer valves are on backwards. and closed means open.
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Old 09-24-2020, 12:05 PM   #47
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Vents were my first thought, but I stared at the schematic and re-read the OP a couple times, and I had to wonder - the problem shows up when the cross-overs are open. I would expect the vents would be an issue with the cross-overs closed. Then the OP stated he filled-up and found one tank way-down, the other over-filled. I have to wonder if there is some sort of contention with the manifold - maybe it's mounted low, not sure if the draws are bottom-tank or top-tank. But it's not a brand new boat so something changed. Manifold has been there a long time.....hmmm...

I like the idea of a crossover with a reversible pump to manually balance when needed (but run closed). Groco makes a 6-port valve that's made to select between two tanks on a single engine - it switches supply and return with a single turn of the handle. One valve per engine (three total, including generator) and you have 100% control of both feed and return. But I have to say, it's a lot of work and money so would definitely figure out the smoking-gun problem. This one is odd....

Good luck, and thanks for sharing.

Peter

Thanks Peter, I appreciate you taking the time. Both supply's and returns run into the top of each tank. The manifold is suspect as well but nothing has changed in that area.

I did change all of the fuel & racor filters prior to and then discovered the stbd transfer valve was closed. The port was already open so I then opened the stbd transfer valve, huge regret although it should not do anything but transfer fuel. Then, I lost power under load, closed both crossover valves, re-primed and she runs great except for the overfilling of the sbd tank, sheese.
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Old 09-24-2020, 12:13 PM   #48
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When you re-open the crossover, do you hear any sound like a suction being released? That would indicate one vent is airing both tanks.


Agreed, the crossover has no effect on fuel to the manifold.



The flare fittings connecting the copper lines can be a source of air, but that doesn't sound like the case.

Thanks for the input. No, I don't hear any air when re-opening.
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Old 09-24-2020, 12:32 PM   #49
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It seems your problems and solution(s) are getting clearer. Fuel flow 101 needs further analysis and you're getting there. Don't forget about a return manifold so you can be 100% sure you're returning to the tank you're drawing from.

As discussed, get those valves handles setup right. Don't guess, remove the fuel line from the valve and check for correct open/close. Mark each valve as to location to and from. While you're at it, put some calibration marks on the sight tubes.
Getting clearer but still a ways to go, thanks for all of the input.

I do have a good understanding of diesels but pale in comparison to you folks, I have learned something everyday on this forum for three years now. With that said, please forgive my rookieness with this question. - if the return line is going straight from the top of the engine directly back into it's fuel tank (port to port or (stbd to stbd)), how could it possibly be returning to the other tank?


Also, will do on the transfer valves and think I'm just going to change out as they are old. Plus, I do not like any valve that takes 15 rotations to shut, this is this weekend's project. The return manifold is ideal but that will need to my spring project as I'm having the boat hauled for the winter next week as we get frozen in here in northern MI.
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Old 09-24-2020, 12:38 PM   #50
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Mike - I really cannot add much here except to say that my hunch is there's something in the plumbing, not the vents (though they are simple to check, so rule-out the easy stuff first). I say this only because your problem appears when crossovers are open vs closed. I do not understand the whole manifold thing, but I guess it's worked for a long time. Obviously, something changed.

Follow-on to Rgano's "Rip it out" comment, I did something close to the attached when I redid my fuel system. I have a single engine with no crossover and return was not switchable - just went to one tank. I was always out of trim. The Groco FV6 valves are a bit pricy - $175/each, but they are great valves and save a ton of fittings/valves. Very clean/elegant solution.

Peter

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Old 09-24-2020, 01:01 PM   #51
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As suggested one of the easiest ways to test the venting is run with the filler caps off. If the engines continue to operate with the filler caps off then the tank venting is restricted. Since the problem shows only when running at higher power then that is what you will have to do. The vents are not likely completely blocked and since fuel use at low revs is hugely reduced the small amount of air is enough to continue to feed the operation. At high power not enough air can enter the tanks so the engines starve.

Another way. Does the shutdown shut you down abruptly or do the engines lose power, slow down and then quit. If the latter then you could also leave the fillers in place but be prepared to loosen them when the slowdown shows. If there is a hiss the venting is the problem. Any hiss is from air being pulled in to the tank.

Vacuum guages would help here hugely. Mounted just after the filters they could tell you if vacuum is building. Use the telltale needle type as they don't need to be monitored constantly. The telltale needle will remain at the highest vac. attained untill you physically reset it. Designated Engineer sells them , good units.

Gate valves are often an air source and have no place in a fuel system for a couple reasons. However, where the stem from the handle enters the valve body there is a nut. Inside the nut is a packing which seals the stem to the valve body and keeps air out and fluid in. That packing can shrink over time and allow air to be pulled into the system. Air can often be pulled in yet no fuel will leak out.
Tighten that nut. I am not really suggesting this is your problem right now but eliminate it as a source.

To me too it sounds like you have a venting problem which creates a vacuum strong enough to choke off fuel delivery. At the least eliminate it as a possibility by clearing the hoses and ensuring the hose are not kinked. It may not be bugs but kinks or a failing hose allowing an inside layer to delaminate and close off the hose interior.
Thanks for your input

Venting - Since the majority that have contributed have ruled that the crossover valves have nothing to do with it, I have checked my side vents externally only as they are blocked inside by fuel tank bulkheads, all clear. I've been running the boat with my fill key in hand ready to vent if I hear it start to die out, 7 hours underway since and no problem except now she is moving fuel unexplained.

Vacuum gauges - I've ordered a set from DE as you suggested, cool site. "Mounted just after the filters" your referring to the racor's, correct?

Checking the gate nut(s) this evening, going to replace with ball valves this weekend.
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Old 09-24-2020, 01:09 PM   #52
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Another silly question -

Since I now have nearly 300 gallons of fuel in each tank, I want to change the crossover valves from gate to ball style which are on the bottom of the tanks, then this part of the thread will be put to bed.



Has anyone used a vacuum on the fuel fill inlets to hold the fuel drip back long enough for me to change out valves? I've seen this done on semi's but then again, they don't have a bilge to clean up.
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Old 09-24-2020, 01:45 PM   #53
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I am VERY familiar with the Jefferson fuel system and consider it a very poorly thought out system, especially that ridiculous "manifold" cylinder where all fuel users encounter a common point. The other hateful thing in your system in the standpipe draw which can allow you to lose fuel prime to the Racors by making one wrong valve setting when opening any one of the Racors.

RIP IT ALL OUT.

Replace both inappropriate tank crossover valves with tees with two ball valves attached, one pair of valves (BOTH normally closed) reconnecting the crossover line and the other pair connecting to the main engine Racors. Downstream of the Racors you can run another cross-connect line with a single ball valve (normally shut) which will enable you to run both engines off one Racor while you quickly open the other to change a clogged filter element. Believe me, it can be done.

A VERY important element in this system would be an electric priming pump with a bypass valve arrangement. I can send a diagram of this highly flexible and successful system I installed in my twin GB42 to your PM if you like.

Hi Rich,
Thanks for your input and I agree with the manifold and think changing out is necessary, are you saying yank it (manifold) and use the cross over valve with T's to replace or is that in addition to changing out the manifold?

"and the other pair connecting to the main engine Racors, Downstream of the Racors you can run another cross-connect line with a single ball valve (normally shut) which will enable you to run both engines off one Racor."

the crossovers are on bottom of tank and supplies come in from manifold to racors - sorry I tried drawing it out but just not getting it

And yes please on the diagram as that would be super helpful - I learn more from you folks than any over-priced big boat mechanic.
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Old 09-26-2020, 09:32 AM   #54
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'Lo All, Shortly after we purchased the Celestial, a 43' 1986 Albin Sundeck trawler w/ twin Cummins 6BT5.9M engines, I had to redo the fuel system plumbing as the old copper lines showed signs of work-hardening due to vibration and not being properly supported, the valve stems were always damp with fuel and the hoses showed signs of deterioration and I wanted to copy Cap'n Wills fuel polishing system. When the fuel tanks were full, there was no air entraining problem, but when the fuel level dropped to the point where the fuel pumps had to suck fuel from the tanks, the Racors quickly filled with air. I wrote a long post about it then, but the short version is this: to cure the problem, I bought the first set of valves at Home Depot. They all sucked air under vacuum (when pulling fuel out of the tanks) from around the valve stems, but under pressure (pushing fuel using a transfer pump) they were fine. I ended up using only Conbraco's Apollo valves. They are certified to be used where a fairly high vacuum is induced. To identify the source of the air leaks, I temporarily replaced all the copper tubing and USCG approved hoses with hose barb fittings and clear vinyl tubing. Air bubbles formed and were visible in the vinyl tubing after each valve when a vacuum was induced. After replacing all the valves with the Apollo valves, there were no air leaks visible in the vinyl hoses. I then installed new USCG approved fuel hoses and had no further problems with the fuel system.
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Old 09-26-2020, 03:21 PM   #55
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Air Leakage and Pressure Drop during Operation.

Feeding the 2 engines and gen set off of a single manifold suggests that you may have an air leak or possible you are pulling a suction on the lines causing air to com out of solution in the fuel to cause an air lock in the lines causing the engine to fail. Have you put a vacuum gage on the manifold it should drop only a few psi below ambient pressure during engine operation at cruise or maximum load rpm.

You could have some blockage in the lines causing a pressure drop. You would see this affect on the gage.

What are you line sizes and flow rates? What is the calculated flow velocity in these max rates in the feed lines. (use the line ID for the calculation) It should be below 10 ft/sec, better would be 5 ft/sec to keep pressure drop low.

I would suggest that rather than a common manifold for the engines you feed from the port tank to the port engine and similarly starboard to starboard engine.

Also, the cross over line appears to be PVC gray plastic Pipe in your picture. A more fuel resistant material would be better if it is plastic.

The cross over line should be closed during operation and use to balance fuel height when engine are not operational if you see a height difference.

Just some of my thoughts
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Old 09-26-2020, 09:35 PM   #56
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To me you should have a separate lines for each engine from each tank. In your current installation you could have a single failure issue (i.e, air leaking into the manifold feeding both engines) that would shut down both engines. Loosing both engines at the same time could be dangerous. As mentioned earlier vacuum gages would help determine if you have issues with flow/pressure drop. The pressure drop in the line engine side of the filters should be less than several psi below ambient pressure at maximum engine flows. If you have a tank shutoff valve you could rig a hand operated vacuum pump at the engine side and see if you have leakage into the line. Something to do at the dock with out engines running.

Have you changed the o'ring seals on the Racors along with the filters the cap and screw handle can leak air if the seals are bad and you have a fair amount of suction pressure.

A comment it appears in you picture of the cross over line that its PVC plastic (gray color tube about 1.5 to 2 inch diameter).
The cross over should be closed and used at the dock for balancing the tanks if the sight gages show a difference in fuel height. Other wise they should be closed during operation and as note be others should have no impact of operation closed.
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Old 09-26-2020, 10:24 PM   #57
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Hi Rich,
Thanks for your input and I agree with the manifold and think changing out is necessary, are you saying yank it (manifold) and use the cross over valve with T's to replace or is that in addition to changing out the manifold?

"and the other pair connecting to the main engine Racors, Downstream of the Racors you can run another cross-connect line with a single ball valve (normally shut) which will enable you to run both engines off one Racor."

the crossovers are on bottom of tank and supplies come in from manifold to racors - sorry I tried drawing it out but just not getting it

And yes please on the diagram as that would be super helpful - I learn more from you folks than any over-priced big boat mechanic.
Here is what worked for me for several decades. You have two tanks; so just ignore the extra two in my diagram. Yes, rid yourself of the manifold and use the crossover with tees. Abandon the standpipes altogether.
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Old 09-28-2020, 04:40 PM   #58
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Here is what worked for me for several decades. You have two tanks; so just ignore the extra two in my diagram. Yes, rid yourself of the manifold and use the crossover with tees. Abandon the standpipes altogether.
Thanks for the drawing, super helpful.
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Old 09-28-2020, 04:59 PM   #59
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Thanks for the response. After all this head-scratching and the response from the members, it really has me thinking that one of my valves has to be backwards.

Reading through the thread to this point, I think it may be a combination of this, as well as a clogged vent on the opposite side.
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Old 09-28-2020, 05:49 PM   #60
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FWIW, I only have a single engine and the fuel system is as it was when I bought the boat. I have a fuel manifold that controls which tank fuel is drawn from and to which tank fuel is returned. The Genset and diesel furnace are not included in that.


I also have a cross line with a transfer pump. It is not necessary, but I find I really like it. It is easy to balance the fuel using it. It can also be very convenient. I usually will transfer most fuel to the Port tank before refueling and then fill up the starboard tank. I normally don't need to have all 400 gallons of fuel, so doing this I end up with about 250-300 gallons of fuel which lasts me a long time.
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