A return fuel what if?

[rgano]

A friend has just modified his boat to allow the single diesel to return fuel to either tank rather than the manufacturer's original setup of return to port tank only. The current set up has the engine's return to a wye equipped with a ball valve in two of the legs. Return fuel enters the wye via the valveless leg and exits via either or both of the other two legs depending upon valve opening.

He asks, "What damage to my Yanmar 6LPA would ensue from me making the mistake of closing both valves?"

I don't really have an answer to that one.

 

[Jeff F]

My experience with Cummins and JD is that the engine will stop immediately if return lines are closed. No harm to anything AFAIK. Open the valve and it runs again.

 

[rgano]

Thanks, Jeff. Since I have the same system, it does concern me too, butI never allow both valves closed at one time. If shifting from one tank to the other, I opn the previously closed valve before closing the other and then double check.

 

[Blissboat]

Given that the builder sets the fuel system up to return only to one tank (typical, in my experience), is there a manifold that allows the Mainship Pilot's two tanks to equalize? Assuming so, is it constricted enough so that the two tanks must be filled independently?

As Rich knows, I am trying to educate myself about MS Pilots, so this is a learning moment.

 

[rgano]

Given that the builder sets the fuel system up to return only to one tank (typical, in my experience), is there a manifold that allows the Mainship Pilot's two tanks to equalize? Assuming so, is it constricted enough so that the two tanks must be filled independently?

As Rich knows, I am trying to educate myself about MS Pilots, so this is a learning moment.

Most of what I know about the topic equalization comes from the 18 months my 30 Pilot II sat in its wet slip (waiting for the lift to be rebuilt) end-on to the back porch where any list was instantly noticed. The fuel system as installed is simple with deck fills to the two saddle tanks and fuel supply valves on each tank at the lower aft corners. The fuel from either tank enters a 3/8" fuel cross connecting hose which has a tee in it from which the engine draws its fuel. Opening both valves theoretically levels the fuel levels of the two tanks. The as-built system returns fuel to only the port tank. Fuel return from my engine is around 12 gallons an hour while burn rate is 8.7 GPH at cruise RPM of 3000 (80% of max fuel use at max HP rating).

So, why was my boat affecting a port list with both tank valves open? I can't say that I know for sure considering that the 200-pound generator is to stbd while the galley cabinetry is to port and batteries are centered. The waste tank to port is only 17 gallons and always empty, and the 40-gallon water tank is centered. When the boat is in the lift, which can the leveled, and the clinometer bubble is on zero, the tanks are self-leveled via the cross connection but leave it in the water with tanks less than full.....

I have pumped a lot of fuel from my 30-gallon dock cart tank into the stbd tank while the boat is in the lift, and the fuel moves across quickly enough if not rapidly; so I know the cross connection is ok. Besides, I replaced that hose at one point to ensure fuel gunk had not collected there.

Another potential issue is, what do you do if your Pilot's port fuel tank develops a leak? You are not going to be able to empty the tank and continue to run the boat from the stbd tank unless you have a way to send all that return fuel to the stbd tank. Two friends with this boat experienced the issue of fuel tank leaks in the last couple of years. One of them just kept running the boat with one tank empty and the other doing duty as supply and return tank until the winter haulout at which time he will have both tanks replaced.

I have made the simple and quick mod to allow the return of fuel to either or both the tanks and typically run returning to both. However, with an additional mod which allows me to monitor the level of both tanks from the helm (why did MS not do this????), I can switch return to the lighter tank until levels return to even.

And that, as Gump said, is all I know about that.

 

[mmullins]

Accidentally ran my Lehman for an entire season with no return and no issues. My mechanic said in low horsepower low fuel demand situations it doesn't really matter. But, in higher horsepower/fuel demand situations the injectors could overheat do to the reused fuel not getting a chance to cool off.

 

[MYTraveler]

My boat has a complicated fuel manifold designed up to allow either main engine and either genset to draw from any of three tanks and to return to any one or more of those three, complicated by a 4th tanks that gravity feeds (if its valve is open) into one of the other three and a pump that allows fuel to be pumped from any of the four tanks to any of the other three. During my "captain's" briefing, one of the most emphatic points made to me was that I should never close off all of the return valves, as catastrophe would surely ensue. The rule was to open one return before closing any other, unless at least two were already open. My boat has Cummins mains and Onan (Cummins) gensets.

 

[Maerin]

You could use a diverter/three way valve. Either/or - would always have flow, just maybe not in the direction you intend if you screw up. But it wouldn't damage anything.


While on the subject, the more options you build into your fuel management, the greater the potential for unintended consequences. Ex: you valve the feed from one tank, return to the other, close the crossover. You're chugging happily along and discover your decks are pink. Ooops! Uh, yes, this is a real possibility. How do I know? Uh huh!!



So don't trust yourself to do the correct thing....

 

[FWT]

"The rule was to open one return before closing any other, unless at least two were already open."

Yep. I was taught "open before closing."

And the reason given was the back pressure will blow various seals, which is catastrophic, and expensive to repair.

This was for Cummins. Your mileage may vary.

 

[Comodave]

Accidentally ran my Lehman for an entire season with no return and no issues. My mechanic said in low horsepower low fuel demand situations it doesn't really matter. But, in higher horsepower/fuel demand situations the injectors could overheat do to the reused fuel not getting a chance to cool off.

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

 

[Delta Riverat]

I always return to the tank I'm drawing from, yeah, don't want fuel on the deck.

I can polish and transfer with the electric pumps which is cool, but I don't transfer with the engines.

I don't know what kind of pressure could be developed in a blocked return but i suspect it could be high enough to cause problems.

 

[Portage_Bay]

On some engines it can cause damage. All depends upon volume and pressure of the return as well as what seals might be over pressured.

 

[HopCar]

I just made a fuel manifold from ball valves and pipe fittings. I could draw from either tank and return to either tank. I don’t think I ever drew fuel from one tank and returned to the other.

Groco makes some interesting fuel valves https://www.groco.net/fv-65038

 

[SIBERNUT]

Had an interesting happening with twin Detroit's. Both tanks pretty much even, so I was drawing from one & returning to the other to get max cooling of the return flow. Both eng stopped, and I had just stuck the tanks. Further investigation revealed one pickup tube was almost 3" shorter than the other.......,..

 

[jleonard]

When I repowered my old Mainship with a Cummins 6BTA 270, I did the same, T’d the return so I could choose which tank to send it to.
One day running down LI sound I saw red coming out of the bilge pump thru hull.
The 1/4 turn valve had vibrated shut. Fuel was spurting out of the clamped hose on the fitting. The clamp wasn’t loose rather the pressure was so great it leaked. Opening the valve stopped the leak.
The engine never skipped a beat.

 

[DDW]

I'd think this might be a problem in a common rail engine? The high pressure fuel rail runs at 30,000 psi in some of them, with the regulator spilling fuel to the return. If the return is blocked, it seems like there could be lots of drama - though maybe it would just shut down by sensing a pressure limit. Don't know if the Volvo in the OP is common rail or mechanical.

 

[Max1]

Why doesn't your friend just use a "Y" valve. In position 1 it feeds the port tank and in position 2 if feeds the starboard tank. The valve can only be in 1 of the 2 positions at any time. Therefore, never a chance of both being closed.

 

[Nick F]

I'd think this might be a problem in a common rail engine? The high pressure fuel rail runs at 30,000 psi in some of them, with the regulator spilling fuel to the return. If the return is blocked, it seems like there could be lots of drama - though maybe it would just shut down by sensing a pressure limit. Don't know if the Volvo in the OP is common rail or mechanical.

Even a mechanical injection diesel produces 3000 - 5000 psi to the injectors. This is certainly enough to overpressure the return line if you dead-end it. You might also overpressure the casing of the injector pump if its drain is connected to the fuel return piping (as it is on my John Deere).

 

[CharlieO.]

I just made a fuel manifold from ball valves and pipe fittings. I could draw from either tank and return to either tank. I don’t think I ever drew fuel from one tank and returned to the other.

Groco makes some interesting fuel valves https://www.groco.net/fv-65038

I went with one of these when I replaced my tanks with plastic tanks. Since there is no crossover on my tanks now, I figured to make it simple this was the ticket. Port, Starboard and off. Fuel only returns to the tank I am drawing from.

 

[twistedtree]

I just made a fuel manifold from ball valves and pipe fittings. I could draw from either tank and return to either tank. I don’t think I ever drew fuel from one tank and returned to the other.

Groco makes some interesting fuel valves https://www.groco.net/fv-65038

This is the ideal way to do it, ensuring that both draw and return are to/from the same tank, and that both are open or closed.

 

[twistedtree]

There are two issues here; back pressure on a closed return, and operational alignment of the valves so fuel comes from and goes to the correct tank and doesn't create a fuel spill or run-dry situation.


You asked about the back pressure issue, and it depends on the engine. Not just the brand, but the specific engine's fuel system. Some engines will be fine, but newer high pressure fuel system engines will suffer severe failure of the fuel pump if the return is blocked. I know numerous boats where this mistake was made and $10,000 later they had a new injection pump. To make this an impossible mistake, Nordhavn no longer installs return valves on any return lines, and instead has all open to the day tank.

 

[twistedtree]

I'd think this might be a problem in a common rail engine? The high pressure fuel rail runs at 30,000 psi in some of them, with the regulator spilling fuel to the return. If the return is blocked, it seems like there could be lots of drama - though maybe it would just shut down by sensing a pressure limit. Don't know if the Volvo in the OP is common rail or mechanical.

Some engines might be set up to shut down on a high return pressure. I was interested to see someone earlier say that the JD & Cummins he was familiar with shut down on high return pressure. Perhaps those were in non-marine applications? I think that behavior is programable in the ECU, but am not certain. I do know that a lot of engines in marine applications are set up to NOT shut down on faults, even severe faults. The rational is that it's better to alarm and let the operator decide whether to stop, or to keep going and risk/sacrifice the engine. But different installations may make different decisions about that.

 

[Jeff F]

Some engines might be set up to shut down on a high return pressure. I was interested to see someone earlier say that the JD & Cummins he was familiar with shut down on high return pressure. Perhaps those were in non-marine applications? I think that behavior is programable in the ECU, but am not certain. I do know that a lot of engines in marine applications are set up to NOT shut down on faults, even severe faults. The rational is that it's better to alarm and let the operator decide whether to stop, or to keep going and risk/sacrifice the engine. But different installations may make different decisions about that.

That was me. Now I'm second guessing my claim. I can say for sure that my JD4045 TFM75 will not run or start with the fuel return closed, and my recollection was that the Cummins BT was the same. My theory when I observed this is that once the back pressure equals the fuel pump pressure the injection pump stops working - I don't think the return line has to reach injection pressure before the engine stops. But this is just a guess on my part.

 

[MYTraveler]

Some engines might be set up to shut down on a high return pressure. I do know that a lot of engines in marine applications are set up to NOT shut down on faults, even severe faults. The rational is that it's better to alarm and let the operator decide whether to stop, or to keep going and risk/sacrifice the engine.

When Cummins gave me a "captain's briefing" on my QSM11's, as part of the delivery process, they told me that although the engines would go into a low power (rpm) mode, they would never shut themselves down due to even the most severe fault condition for exactly that reason, adding that it is not even programmable because Cummins fears liability claims if the engines do shut themselves down at the worst time. On the other hand, the Onan/Cummins genset would shut themselves off for even relatively benign conditions.

 

[CaptTom]

...because Cummins fears liability claims if the engines do shut themselves down at the worst time..

Good! I once had a boat with gas Mercruiser I/O drives. Those stupid things would shut off for the smallest issue. I lived in fear of the day they'd do that when I needed them most.

Yes, manufacturer, there may be times when we choose to sacrifice your motor so that we can get home alive. No point in having a perfectly healthy engine sitting on the bottom in a wreck.

 

[luna]

To make this an impossible mistake, Nordhavn no longer installs return valves on any return lines, and instead has all open to the day tank.

Thats interesting.

Does Nordhavn also restrict the selection of the fuel supply tank to just the day tank?

If not, you could select the supply to come from one of the storage tanks and potentially overfill the day tank with the return.

If so, that would require you to purposely run a fuel transfer pump (assuming the day tank is higher than the storage tanks) to replenish the day tank. That also runs the risk of overfilling the day tank, if left unattended.
Perhaps the transfer pump is controlled by a system that shuts it off when the day tank is near full or its on an adjustable timer.
Additionally, should your fuel transfer system fail, your range is now limited to the current contents of the day tank.

Myself I would prefer a more flexible system where you could draw from and return fuel to, any tank.
I have 4 tanks and 4 consumers. 8 four way valves, some fittings and fuel line accomplishes that task without the need for any transfer pump.

 

[rslifkin]

Thats interesting.

Does Nordhavn also restrict the selection of the fuel supply tank to just the day tank?

If not, you could select the supply to come from one of the storage tanks and potentially overfill the day tank with the return.

If so, that would require you to purposely run a fuel transfer pump (assuming the day tank is higher than the storage tanks) to replenish the day tank. That also runs the risk of overfilling the day tank, if left unattended.
Perhaps the transfer pump is controlled by a system that shuts it off when the day tank is near full or its on an adjustable timer.
Additionally, should your fuel transfer system fail, your range is now limited to the current contents of the day tank.

Myself I would prefer a more flexible system where you could draw from and return fuel to, any tank.
I have 4 tanks and 4 consumers. 8 four way valves, some fittings and fuel line accomplishes that task without the need for any transfer pump.

If the day tank is higher than the other tanks, you could also add lines and valves to allow the day tank to overflow back to one of the other tanks.

 

[kapnd]

My boat came to me with the fuel return check valve installed backwards.
Had about a 15 hour voyage back to home port, during which we lost a few gallons into the bilge. It leaked around the clamp, like mentioned above.
No apparent damage to the fuel system, just a big cleanup in the bilge.
Have put a couple thousand hours on since, so I’m pretty confident it didn’t hurt the pump.

 

[mahal]

Most of what I know about the topic equalization comes from the 18 months my 30 Pilot II sat in its wet slip (waiting for the lift to be rebuilt) end-on to the back porch where any list was instantly noticed. The fuel system as installed is simple with deck fills to the two saddle tanks and fuel supply valves on each tank at the lower aft corners. The fuel from either tank enters a 3/8" fuel cross connecting hose which has a tee in it from which the engine draws its fuel. Opening both valves theoretically levels the fuel levels of the two tanks. The as-built system returns fuel to only the port tank. Fuel return from my engine is around 12 gallons an hour while burn rate is 8.7 GPH at cruise RPM of 3000 (80% of max fuel use at max HP rating).

So, why was my boat affecting a port list with both tank valves open? I can't say that I know for sure considering that the 200-pound generator is to stbd while the galley cabinetry is to port and batteries are centered. The waste tank to port is only 17 gallons and always empty, and the 40-gallon water tank is centered. When the boat is in the lift, which can the leveled, and the clinometer bubble is on zero, the tanks are self-leveled via the cross connection but leave it in the water with tanks less than full.....

I have pumped a lot of fuel from my 30-gallon dock cart tank into the stbd tank while the boat is in the lift, and the fuel moves across quickly enough if not rapidly; so I know the cross connection is ok. Besides, I replaced that hose at one point to ensure fuel gunk had not collected there.

Another potential issue is, what do you do if your Pilot's port fuel tank develops a leak? You are not going to be able to empty the tank and continue to run the boat from the stbd tank unless you have a way to send all that return fuel to the stbd tank. Two friends with this boat experienced the issue of fuel tank leaks in the last couple of years. One of them just kept running the boat with one tank empty and the other doing duty as supply and return tank until the winter haulout at which time he will have both tanks replaced.

I have made the simple and quick mod to allow the return of fuel to either or both the tanks and typically run returning to both. However, with an additional mod which allows me to monitor the level of both tanks from the helm (why did MS not do this????), I can switch return to the lighter tank until levels return to even.

And that, as Gump said, is all I know about that.

The reason why the cross connection between your tanks didn’t equalize the fuel between them when your boat was docked with a list is because the fuel would have to move upwards. Instead fuel will move to the tank with more fuel exacerbating the list.

 

[rgano]

The reason why the cross connection between your tanks didn’t equalize the fuel between them when your boat was docked with a list is because the fuel would have to move upwards. Instead fuel will move to the tank with more fuel exacerbating the list.

Indeed, but once I had the fuel evenly distributed as indicated by the sight gauge, the boat still developed a list at the pier due to unfindable offside weight.