A return fuel what if?

[Barking Sands]

I dont know if there are bypass circuits in the various high pressure pump types. I just did a little looking and didnt see anything for protection from the scenario described. In addition if there was such a valve it likely would be prone to occasional failure and I have never heard of that scenario as evidence of its existence.

Of course on common rail there are bypass valve at the rail. but only so that pressure can go to return.

I dont have detailed schematics but on first glance it appears that scenario would likely be bad in various way. Most return lines are made up of copper tube that has a pretty low working pressure. But burst pressure can be substantially higher. My opinion is the pump would be damaged by way of shafts, pins or castings.

We once had an incident where a crew was troubleshooting a hydraulic issue on an aircraft. The pump is driven off the engine accessory drive. For some reason the tech capped off the "case drain", which is simply a drain to collect the seepage from the moving parts of a hydraulic pump. Once pressure equalized it came apart catastrophically. Good thing it was just ground runs.

I dont think engineers accounted for the "no return path" scenario since it should not be an option.

I personally would just do a 3 way valve. left/right/both

 

[bkcorwin]

Lugger 1276 has a internal pressure relief valve and bypass at the fuel transfer pump.

I dont know if there are bypass circuits in the various high pressure pump types. I just did a little looking and didnt see anything for protection from the scenario described. In addition if there was such a valve it likely would be prone to occasional failure and I have never heard of that scenario as evidence of its existence.

Of course on common rail there are bypass valve at the rail. but only so that pressure can go to return.

I dont have detailed schematics but on first glance it appears that scenario would likely be bad in various way. Most return lines are made up of copper tube that has a pretty low working pressure. But burst pressure can be substantially higher. My opinion is the pump would be damaged by way of shafts, pins or castings.

We once had an incident where a crew was troubleshooting a hydraulic issue on an aircraft. The pump is driven off the engine accessory drive. For some reason the tech capped off the "case drain", which is simply a drain to collect the seepage from the moving parts of a hydraulic pump. Once pressure equalized it came apart catastrophically. Good thing it was just ground runs.

I dont think engineers accounted for the "no return path" scenario since it should not be an option.

I personally would just do a 3 way valve. left/right/both

 

[Barking Sands]

Lugger 1276 has a internal pressure relief valve and bypass at the fuel transfer pump.

Fuel transfer pump? Have a good fuel schematic of that particular engine?

There are various types of pressure relief and bypass valves. Some will divert flow to return, creating a large loop (back to the tank). Others will divert flow to pump suction to create a short loop. It all depends on where they "relieve" to or "bypass" to as to whether it may be catastrophic in regards to the original scenario. If these bypass and relief valves do not create the short loop upon activation then they would send the relief and bypass to the return.

With out a detailed schematic its impossible to tell. But in general, blocking any return path in a hydraulic system is bad news.

 

[Barking Sands]

Thinking more...If it is a new fancy common rail with lots of computer control it may sense rail over pressure and shut down, or derate? Not sure what they are capable of.

Again, thinking further on the basic pump/injector set up it could be that the back pressure simply causes the "full displacement" of each pump stroke to be discharged out the injector causing an over fueling condition. It would essentially make the injectors the bypass valves in the system and the system would run at whatever the injectors cracking pressures were set to in a continuous fashion instead of rising and falling pressures. I was just rebuilding my little Westerbeke injectors and I think that was set to 2200psi. So essentially every line after the high pressure pump would remain at 2200PSi, including the return lines. Not sure of possible failures in that scenario. Things would get weird though...lol.

 

[RickyD]

Lehmans return almost no fuel as compared to some other brand engines that return a whole lot.

I don't know about that. I had Lehman 275s in my last boat and once, after a mechanic had been aboard, I started the engines when my guests arrived. After letting them in the gate, and as I returned to the boat I could see fuel squirting out the vent. I mean with pressure behind it. I fired the mechanic. I will admit the fuel valves could be a little confusing unless you took a moment to think about it.

On my Cat 3208s they say not to switch over tanks with the engines running. Now I have a valve for each of my two tanks that directs the fuel. It is either to this tank or that and from this tank or that. I have been afraid to even switch them over quickly. I'm probably worried about nothing.

 

[TBW]

just dont return to a full tank
you'll leave a "trail"

 

[Brooksie]

Better to use a valve that has one or the other port open always, wye valve, than two valves that can both be shut off. I too would be more worried about returning to a full tank.

 

[Circumnavigator]

Two thoughts:
All of this cries out for having a day tank. With one, you always have a day's worth of fuel that you know has been through a good filter and you have a place to return fuel. I see no reason to want to bypass the day tank and draw fuel from a main. All three of the boats below had day tanks.


Second, if you are going offshore, you will want to keep all but one of the main tanks either full or empty to minimize free surface. 400 gallons (a ton and a half) of fuel sloshing around in a 500 gallon tank has a serious effect on stability. You must have one tank in that state, but there's no reason to have two.


Jim


Sweetwater - Swan 57 sloop - circumnavigated 1995-98
Fintry - x Royal Navy Fleet Tender 2003-22 20k miles including transatlantic The Fleet Tender Fintry
Morning Light -- Webbers Cove 42 trawler 2021- 23
Going back to sailing now that Morning Light is sold.

 

[Darlin]

Tanks will stabilize. I once closed one tank to correct what I thought was a list. I soon forgot I had done this but remembered when I developed an opposite list. I opened the other tank and fuel was equalized in a few days. Usually fuel floes from each tank to a manifold with three out valves; port & starboard engines and gen set.

 

[Comodave]

I don't know about that. I had Lehman 275s in my last boat and once, after a mechanic had been aboard, I started the engines when my guests arrived. After letting them in the gate, and as I returned to the boat I could see fuel squirting out the vent. I mean with pressure behind it. I fired the mechanic. I will admit the fuel valves could be a little confusing unless you took a moment to think about it.

On my Cat 3208s they say not to switch over tanks with the engines running. Now I have a valve for each of my two tanks that directs the fuel. It is either to this tank or that and from this tank or that. I have been afraid to even switch them over quickly. I'm probably worried about nothing.

Well I have never tested that but that information came directly from Bob Smith. I took his last Lehman seminar and that question came up. He said they return almost no fuel. I guess you could argue with him but he passed away not long after that seminar.

 

[luna]

Two thoughts:
All of this cries out for having a day tank. With one, you always have a day's worth of fuel that you know has been through a good filter and you have a place to return fuel. I see no reason to want to bypass the day tank and draw fuel from a main. All three of the boats below had day tanks.


Second, if you are going offshore, you will want to keep all but one of the main tanks either full or empty to minimize free surface. 400 gallons (a ton and a half) of fuel sloshing around in a 500 gallon tank has a serious effect on stability. You must have one tank in that state, but there's no reason to have two.


Jim


While I agree that a day tank is certainly a benefit, there is to me a valid reason to be able to access the fuel in the main tank.

Should your transfer system that fills the day tank fails, it would be far more pleasant to simply turn a few valves to draw fuel from the main tank, rather than diagnose, repair or replace the failed parts of the transfer system while you are getting jostled about offshore.

WRT the full tank reasoning, that would mean that should you have 2 main tanks (common) and they are outboard of the engines (again common) at some point all of the fuel load is on one side. Your 1.75 tons of fuel will certainly have an effect on the list and therefore the ride of the average 60' vessel. Baffles in the tank are there to reduce the free surface effect of a partially full tank. I use mine each time I'm underway. They seem to work just fine.

As with most things, it depends.

 

[mahal]

Well I have never tested that but that information came directly from Bob Smith. I took his last Lehman seminar and that question came up. He said they return almost no fuel. I guess you could argue with him but he passed away not long after that seminar.

Is it possible that Bob Smith was talking about a 120hp Lehman?

 

[psneeld]

I have heard that Lehman 120's return almost no fuel but the bigger 225's or whatever return much more. Different injection system.

LarryM (moderator) I think has posted some info on that before....see if he responds or someone can PM him if interested.

If correct, using Bob Smith's advice is good but has been so bastardized on the net...it is getting weak.

 

[RickyD]

Well I have never tested that but that information came directly from Bob Smith. I took his last Lehman seminar and that question came up. He said they return almost no fuel. I guess you could argue with him but he passed away not long after that seminar.

If you read my post I fired the mechanic but that was really because it was the second time he mixed up my valves. When my wife and I took it out for the first time he had swapped the valve settings and the fuel was coming out of one tank and into another. I ran it out of fuel in the middle of San Diego harbor. When I scrambled into the engine room looking for the reason both my engines quit I saw the problem. Fixed it, then I had to prime the port engine, luckily I had already been instructed on how to do that, and started it. I had my wife driving, turned around to head back. For the stb engine I had to tilt up a heavy couch, tie it to overhead hand rails, lift up the floor panel, find the hot primer button, push like crazy, and finally start it.

So I guess Bob may have been talking about a 120 because my turbo 275s pulled lots of fuel.

 

[rgano]

Two thoughts:
All of this cries out for having a day tank. .

We are talking mere 30-foot boats here with zero space for such a thing.

 

[ronobrien]

3 way valves are made that would eliminate that possibility, although you could no longer select both tanks.

 

[Comodave]

If you read my post I fired the mechanic but that was really because it was the second time he mixed up my valves. When my wife and I took it out for the first time he had swapped the valve settings and the fuel was coming out of one tank and into another. I ran it out of fuel in the middle of San Diego harbor. When I scrambled into the engine room looking for the reason both my engines quit I saw the problem. Fixed it, then I had to prime the port engine, luckily I had already been instructed on how to do that, and started it. I had my wife driving, turned around to head back. For the stb engine I had to tilt up a heavy couch, tie it to overhead hand rails, lift up the floor panel, find the hot primer button, push like crazy, and finally start it.

So I guess Bob may have been talking about a 120 because my turbo 275s pulled lots of fuel.

That could be true.

 

[rgano]

3 way valves are made that would eliminate that possibility, although you could no longer select both tanks.

Not being able to send to BOTH or either is a non-starter for me.

 

[rslifkin]

What about adding a relief valve to the fuel return manifold that opens at a set pressure, say 3 psi? Then if you accidentally closed all of the return valves it would vent through the relief back to whatever tank that is plumbed to.

 

[Duke 239]

If you read my post I fired the mechanic but that was really because it was the second time he mixed up my valves. When my wife and I took it out for the first time he had swapped the valve settings and the fuel was coming out of one tank and into another. I ran it out of fuel in the middle of San Diego harbor. When I scrambled into the engine room looking for the reason both my engines quit I saw the problem. Fixed it, then I had to prime the port engine, luckily I had already been instructed on how to do that, and started it. I had my wife driving, turned around to head back. For the stb engine I had to tilt up a heavy couch, tie it to overhead hand rails, lift up the floor panel, find the hot primer button, push like crazy, and finally start it.

So I guess Bob may have been talking about a 120 because my turbo 275s pulled lots of fuel.

This is why I am looking for a walk in engine room. Easy access means no relying (or no excuse for relying) on someone else to do basic things like line up the fuel, open seacocks, check Raycors, look (with my eyes) for leaks, check bilges, etc. etc. But most of all, no sofas involved in mechanical operations.

 

[ronobrien]

I know this isn't the correct procedure, but I have never started a new thread and I can't find the "NEW THREAD" button on the CP. Can anyone give me some direction please? Thank you. Happy Thanksgiving

 

[CharlieO.]

I know this isn't the correct procedure, but I have never started a new thread and I can't find the "NEW THREAD" button on the CP. Can anyone give me some direction please? Thank you. Happy Thanksgiving

Click the Forum button at the top of the page, click which topic you want to post in, then click new thread.

 

[ronobrien]

Click the Forum button at the top of the page, click which topic you want to post in, then click new thread.

I'll check it out, thank you. Happy Thanksgiving.

 

[SteveK]

I can confirm the 120 Lehmans do not return much if any fuel. In an attempt to use the engines to transfer fuel I set both to draw from the fuller tank and return to the lower tank. With only sight tubes for fuel levels marked with zip tie, the fulle tank as expected used fuel, the lower tank level was neglible. But after many hours set this way the tanks became equal by drawing down from the fuller tank.