Cabin Heater Tank

[Roger Long]

I discovered that my main fuel tank is just a few inches too low for gravity feed to the Newport diesel cabin heater I'm installing. I don't want to be dependent on a pump or have to listen to it clicking so I'm having a small gravity tank made.

I have a fuel polishing system on my boat that is circulating fuel whenever the engine is running.

http://www.rogerlongboats.com/FOpolishing.htm

So, how cool is this?

The 1.5 gallon tank is simply inserted in the line that runs from the polishing system back to the main fuel tank. It thus fills automatically with just filtered fuel when ever the engine is running and this fuel is constantly renewed. If I run the stove for a long time and need to refill the tank, I just turn on the polishing pump for a few minutes. No lugging Jerry jugs around, no worry about over pumping and spouting fuel out the vent.

Although the tank is unlikely to overfill, the vent does need to have a check valve on it just in case. The Forespar replacement cap and duckbill valve for their anti-siphon loops can be screwed onto a 1/4" NPT x 1/4" tube compression fitting like the parts were made for each other, which, maybe they were.

The length of copper tube will stick up without support to the highest point I can reach with it up in the cockpit coaming. The air bubble in the tube and the top of the tank should prevent oil from ever reaching the little joker valve.

 

[sailingdog]

very nice... but is there a risk of you pumping dirty fuel into the heater day tank, since it is in the fuel polishing line.

 

[Roger Long]

is there a risk of you pumping dirty fuel into the heater day tank, since it is in the fuel polishing line.

No dirty fuel on my boat! That's why there's a polishing system

The tank is just downstream from the polishing system filter so is probably the cleanest fuel on the boat. The heater has it's own filter with shut off downstream from the tank so I'm not expecting any fuel problems with it.

 

[Bob J.]

If you put the check valve on the vent to prevent overflowing the tank, you will create a vacuum within the day tank whenever the heater is running. Can you run the vent off the day tank & tie it in with the vent off your main fuel tank? This will allow the day tank to breathe & prevent a vacuum.

 

[sailingdog]

LOL...remember you said this when the fuel gods clog up your heater...

No dirty fuel on my boat! That's why there's a polishing system

The tank is just downstream from the polishing system filter so is probably the cleanest fuel on the boat. The heater has it's own filter with shut off downstream from the tank so I'm not expecting any fuel problems with it.

 

[Roger Long]

you will create a vacuum within the day tank whenever the heater is running.

Turn that check valve around in your mind.

 

[Bob J.]

Turn that check valve around in your mind.

That makes sense. Hope it works out for you!

 

[All U Get]

Hi Roger,
How much lower would your heater have to be in order to have it gravity feed? I'm thinking those home units must be similar.
All U Get

 

[druid]

Looks excellent, Roger! Of course, the Process Control Engineer in me says install a level switch at the top of the tank (above the return outlet) connected to the pump. No overflow, no pressure in the tank, no check-valve required.

druid

 

[Roger Long]

How much lower would your heater have to be in order to have it gravity feed?

Right on the cabin floor for minimal performance and below it for optimum. There's also a hatch there for wiring access and I'd like the heater up just a few inches so that the valve doesn't get kicked and I can clean under it.

 

[Roger Long]

Of course, the Process Control Engineer in me says install a level switch at the top of the tank (above the return outlet) connected to the pump. No overflow, no pressure in the tank, no check-valve required.

The Process Control Engineer in you isn't looking at the full picture. The tank simply overflows to the atmospheric pressure discharge of the polishing system into the main fuel oil tank and vents indirectly through the main fuel system vent. It's automatically self leveling and pressure regulating with no switches or wiring that can fail. There is not check valve. The 1/4" copper line at the top of the tank with the anti-siphon duckbill valve in it is only there to make sure the stove will gravity feed in the rare instance when the main fuel tank is so full as to block the air path between the main fuel oil fill and the vent.

You have to look at the whole system to understand how this works:

The heater tank goes where it says 3/8" at the top of the loop in the green polishing system line.

See if the Process Engineer in you can figure out what happens if the Racor filter loads up and I open the purple valve which is located just behind a small door under the companionway. Then, if the polishing system also loads up and shuts down right after, what happens to the gallon of just filtered fuel in the heater tank? That gallon will keep me going for another hour while I maneuver to a safe location.

 

[sailingdog]

Very nice design Roger... provides you with a safety fuel tank that is gravity fed in an emergency.

 

[druid]

The Process Control Engineer in you isn't looking at the full picture. The tank simply overflows to the atmospheric pressure discharge of the polishing system into the main fuel oil tank and vents indirectly through the main fuel system vent.

Actually the PCE in me says if input is greater than output, Bad Things Happen. If the outlet cannot keep up with the pumped-in fuel, it will go up your vent pipe, eventually either going out the vent and polluting the environment or pressurizing the tank.

As long as you can ENSURE the outlet will always keep up with the inlet, you're ok.

(LOVE the diagram!)

See if the Process Engineer in you can figure out what happens if the Racor filter loads up and I open the purple valve which is located just behind a small door under the companionway. Then, if the polishing system also loads up and shuts down right after, what happens to the gallon of just filtered fuel in the heater tank? That gallon will keep me going for another hour while I maneuver to a safe location.

The PCE says if the outlet is at the TOP of the tank, that gallon will stay right where it is unless you turn the boat upside-down.

But I am nit-picking: it's an excellent design.

druid

 

[Roger Long]

if input is greater than output, Bad Things Happen.

I am increasing the size of the outlet to 1/2" and it has no restriction on it. The reason for the Forespar MF 841 joker valve vent and small 1/4" tubing vacuum break line is to create an air bubble in the top part of the tank. The air bubble should keep fuel from ever reaching the little rubber valve.

The PCE says if the outlet is at the TOP of the tank, that gallon will stay right where it is unless you turn the boat upside-down.

Gotcha. If the flow from the polishing system stops due to either pump or filter failure when the engine is running on the emergency secondary crossover from that system, the polishing system flow to the heater tank reverses and becomes a gravity supply to the engine. That's nearly an extra hour of running time (more if I slow down) in which to get out of danger or get the Racor filter element changed. This feature is totally automatic. The only drawback is that I may not know that it has engaged until the engine is sucking air. However, the drill once I have turned the red emergency valve is to get anchored or the primary Racor filter changed ASAP.

Another feature to note: If I'm really in a tight spot and the engine mounted filter is loading up or the mechanical engine mounted pump is failing, I can gradually close the isolation valve and direct the full 28 psi of the polishing system to the engine. Bad things could happen that might require repair or clean up later but it's a last ditch option that might keep the engine limping along enough to get me clear of a danger.


But I am nit-picking: it's an excellent design.

druid[/quote]