Connecting heater diesel overflow to main fuel tank?

[patrickkidd]

I am installing a Dickenson Newport diesel heater in my Catalina 30. It has a 1/4" diesel overflow line which I have run back to the tank. The Catalina 30 tank has a return line (I assume) run back to the M25 engine. Would it work to put a tee in this return line and connect the heater overflow to that?

Seems like it would make sense but I don't know enough about diesel return lines.

Thanks!

 

[dlochner]

The diesel return line from the engine will be pressurized. A line tee'd into that return line will become pressurized, which in your case, you don't want as it may back flow into the heater. A check valve in the heater return line might work, but the better solution is to follow the heater manufacturer's recommendations.

 

[patrickkidd]

The diesel return line from the engine will be pressurized. A line tee'd into that return line will become pressurized, which in your case, you don't want as it may back flow into the heater. A check valve in the heater return line might work, but the better solution is to follow the heater manufacturer's recommendations.

Thanks for the info on the return line. The manufacturer has no recommendations. I suppose I could drill my own tank vent fitting. Or replace the fuel gauge sender with a model that has a vent.

 

[Jake N Eggs]

The return line should not be pressurized at the tank. Some systems hold a positive pressure just beyond the injectors but the fuel then runs unobstructed to the tank. I would think that it would be possible to have a tee right at the tank and combine the returns. The only problem that I could anticipate, if the combined flow volumes exceeded the capacity of the line going into the tank it could introduce back pressure.

 

[Gunni]

What Jake said, I have a genset return that tees into my engine return line right at the tank. This eliminates the need for a new tank penetration and has worked flawlessly for years. It was installed by a master ships mechanic as part of a pro install. I will note that my genset has a dedicated tank supply using an extra tank fitting provided by Beneteau OEM.

 

[patrickkidd]

What Jake said, I have a genset return that tees into my engine return line right at the tank. This eliminates the need for a new tank penetration and has worked flawlessly for years. It was installed by a master ships mechanic as part of a pro install. I will note that my genset has a dedicated tank supply using an extra tank fitting provided by Beneteau OEM.

The return line should not be pressurized at the tank. Some systems hold a positive pressure just beyond the injectors but the fuel then runs unobstructed to the tank. I would think that it would be possible to have a tee right at the tank and combine the returns. The only problem that I could anticipate, if the combined flow volumes exceeded the capacity of the line going into the tank it could introduce back pressure.

Thanks you two. I'll go for it then. The only other thing I am worried about, as warned by the heater manufacturer, is backfill into the heater via the return valve because the main tank vent is higher than the heater itself. But I suppose a check valve or shutoff will work there.

 

[dlochner]

The return line should not be pressurized at the tank. Some systems hold a positive pressure just beyond the injectors but the fuel then runs unobstructed to the tank.

If there is no pressure in the return fuel line, then how does the excess fuel return to the tank?

The only other thing I am worried about, as warned by the heater manufacturer, is backfill into the heater via the return valve because the main tank vent is higher than the heater itself. But I suppose a check valve or shutoff will work there.

I just took a look at the manual. (‎dickinsonmarine.com/dm/wp-content/uploads/2017/03/Diesel-Heater-Manual-2016-1.pdf) The purpose of the return line on the diesel and the purpose of the return line on the heater are different. The heater is designed to burn all the fuel supplied to the burner, however, under some conditions, fuel may escape from the oil (fuel) metering valve. The return line collects this fuel and returns it to the tank. If the fuel tank is below the level of the valve, then gravity will drain the fuel back to the tank. If the top of the tank is above the heater valve, then what?

The return line must go into the top of the fuel tank. If the tank is over filled, meaning the hose filling the tank is full, then there will be pressure on the return line and fuel will go out the return line and then flood the heater. The solution the manufacturer offered is to install a shutoff valve in the return line. They specifically state that a check valve should not be used. Check valves can stick in the open position, if that occurred, fuel could back flow out of the return line and back into the heater.

My suggestion is that you contact the manufacturer and ask their advice. It may be possible to install a T at the tank, however, it would need to be installed in such a way that fuel returning from the engine's fuel pump could not enter the return line for the heater.

The consequences of a bad install could be disastrous, it will be far better to rely on the manufacturer's advice.

 

[patrickkidd]

The return line must go into the top of the fuel tank. If the tank is over filled, meaning the hose filling the tank is full, then there will be pressure on the return line and fuel will go out the return line and then flood the heater. The solution the manufacturer offered is to install a shutoff valve in the return line. They specifically state that a check valve should not be used. Check valves can stick in the open position, if that occurred, fuel could back flow out of the return line and back into the heater.

Yes that is correct, and thanks for the reminder on not using a check valve. The main tank is below the heater, so we are talking about the same condition where the main tank is overfilled which will flood the heater. The heater manufacturer suggests using a shutoff-valve on the overflow line so that's what I will do. Or just never fill the tank all the way to the top, watching the fuel gauge as I fill.

 

[LeslieTroyer]

The return line is not”pressurized” in the sense of having 5 psi like the delivery line. It only has enough (back) pressure to overcome the friction in The fuel line running back to the tank.

It’s probably only 5-8 feet more to go to the tank vs “T”ing the return line. I’d probably keep the systems separate to reduce troubleshooting and maintenance issues later ( ie replacing the return line and forgetting about the heater return)

Les

 

[patrickkidd]

So I ended up putting a tee in the return line right at the tank. There was no fuel in the return line when I cut it. All looks good.
Thank you all!

 

[SG]

The return line from the heater needs to run by gravity back to the fuel tank. I don't think you can depend on a siphon action, so I'd be concerned about the route being self draining. You don't want to be sailing on the wrong tack and have things operating differently. (IF,for example, the fuel tank top on on tack ends up higher than the heater, gravity won't be working the same as at a calm anchorage.)

The feed from the engine return is not pressurized -- but the fuel is only going to take the "path of least resistance". So I'd be careful with the "T", it's position, lead, etc.

I think the DLochner's suggestion about consulting with Dickerson is a good idea. When you speak with them, talk about the whole routing, the relative heights, what happen on different tacks, etc.

 

[JimInPB]

A pressure gauge is worth a thousand guesses.

 

[SG]

A pressure gauge is worth a thousand guesses.

In what sense Jim?

 

[JimInPB]

If you think that the place you want to T-in your return might be under pressure, then check it with a pressure gauge. Then you are not guessing any more.

 

[SG]

I think the issue will be if it will always be out of the normal flow. The boat heels, and the line to the Dickerson may end up with being the low side—then unintended consequences. Not jus a jammed up discharge would result, it might be really draining back in an unintended way