Remove Plug in Fuel Tank Question

I would like to remove a plug at the bottom of my fuel tanks and install a valve for a future fuel polishing system. These tanks are on my Nordic Tug 42 and hold 300 gallons each. Right now, about 100 gallons remains in each tank. I could be completely off base, but I'm thinking that if I block all possible avenues for air to enter the tank when the plug is removed, that very little diesel will escape before I get the valve screwed in.

Am I asking for a disaster or will this work? I heard from something I read that hooking up a vacuum cleaner on the fuel fill opening to create a vacuum in the tank works so well that no diesel will escape from the tank. But I have a huge volume in the tank right now, so I wonder if this method is workable. I could fill the tanks to capacity as fuel is pretty cheap right now but then I may have a bigger disaster. I just don't know.

Yes it works, I recommended this to the mechanics when we where having a generator installed and it save time and money draining the fuel tank and refilling. I first heard about doing this from a master plumber, they would make the hot water heater air tight and change out a electric heater element without having to drain the tank. A fast way to seal hose fittings is to place a bolt the same size as the I.D. of the hose and seal it off with a hose clamp if you don't have the right threaded plug fittings
Bill.

That's a great challenge Ron... I know if I replace an LP fuel regulator on a forklift (and the two coolant hoses that attach and pass through it) and the engine is cool/ unpressurized- I can make the line swap in about 30 seconds and hardly lose any coolant. That would be a coolant system completely filled and the cap LEFT ON.
Just thinking that on your case, with only a partial tank, the air may have a negative effect. I know air will compress and fluids generally don't. I wonder if air will "expand" under a vacuum like you are considering trying???
Standing by...


Forky
1983 Present 42 Sundeck
Twin Lehman 135's

I've never attempted it but learned on the GB Owners Forum that hooking a shop vac to the fuel fill will work just fine. Good luck.

Howard

If there is any air in the tank IMO fuel will come out. If the tank were absolutely tip top full like a water heater maybe not.
Fill a wine bottle and invert it and see what happens.

Why not just pump the 100 gal into the other tank to install the valve? It can't take much more effort that sealing off the tank and jury-rigging a shop-vac.

FlyWright said:

Why not just pump the 100 gal into the other tank to install the valve? It can't take much more effort that sealing off the tank and jury-rigging a shop-vac.

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Or just pump the fuel into a couple of 55 gallon drums. Poly drums are less than $70 each. How many boat projects do we all do that go as planned? If this one goes south.

Pump one tank into other, install then repeat.

FlyWright said:

Why not just pump the 100 gal into the other tank to install the valve? It can't take much more effort that sealing off the tank and jury-rigging a shop-vac.

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Thanks, but to have that capability I need to get a valve installed on the second 1/2" NPT fitting that is right next to the engine fuel feed fitting. Then I could install a pump and filter to move fuel so getting a valve on this spare fitting is the first step.


The way Nordic did this fuel system is the port tank feeds the main engine and the starboard tank feeds the generator. There is a cross over hose to keep the tanks somewhat level. Can't imagine why they did it this way and I would like to correct it.

Do you have a shut-off valve on the crossover line?

What is it about the current setup that you don't like?

Ron,

I also heard about the vac method from a Master Plumber. I used it on a leaking home heating oil tank. Worked great on a 275 gallon tank with about 75 gallons of oil.

Rob

I hit some key and lost everything I typed. Is there some undo function when typing a message?

FlyWright said:

Do you have a shut-off valve on the crossover line?

What is it about the current setup that you don't like?

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Second try. Yes, I have valves on the crossover line.

The current system doesn't allow me to transfer fuel from tank to tank and I would like to be able to polish the fuel as I believe I have some black bugs in my tanks as seen on the filters. I would like something like my previous boat where I had control of which tank to draw fuel from and which tank to return fuel to. So the first step is to get access to the second fitting on each tank that is presently plugged. This fitting is right at the bottom of the tank and close to the fuel supply fitting.

I could use some help Al. What to come up?

I've done the shop vac trick before. Works like a champ. First I hooked a water manometer to the vac and figured out the suction to make sure it could overcome the head in the tank, once satified with that, rock on. I do have a vac where motor brushes are not in the process flow, so I was comfortable about fire prevention. But vac was on gunwale so if it ignited, I'd kick the bitch into the water.

Ski in NC said:

I've done the shop vac trick before. Works like a champ. First I hooked a water manometer to the vac and figured out the suction to make sure it could overcome the head in the tank, once satified with that, rock on. I do have a vac where motor brushes are not in the process flow, so I was comfortable about fire prevention. But vac was on gunwale so if it ignited, I'd kick the bitch into the water.

Click to expand...

you make your Admiral stand there and hold the vac??

mine would be pissed if ....

#1, i had her hold a flaming vac..

#2. i kicked her in the water because of said vac..



HOLLYWOOD

windmist said:

I could use some help Al. What to come up?

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Hmmmmm... Sounds very tempting!

The time it will take to pull the plug and screw in the valve will only be a gallon or two with a 1/2 or 3/4 fitting.

A pail or deep tray will be fine.

A safety precaution would be to reinstall the plug into the valve discharge when the work is done.

We do this annually when looking for water in the bottom of the fuel boxes.

Do you have a straight shot from fuel fill into tank such that you can insert a pickup hose attached to your fuel transfer pump?

Another method is to hook up your new fuel transfer pump to the existing fuel line from "first" tank and transfer to other tank. Then with a properly sized rubber stopper with a tube through it and valved hose attached, insert into plug threads and transfer remaining fuel via gravity or again move with your fuel transfer pump.

Per chance if you remove plug that method may prove a bit too messy if valve does not quickly and easily fit. A back up plan or two is not a bad idea.

I've done a couple of these over the years. As long as you have good access to the tank plug, use of a container to catch the fuel, and have the plug and valve ready to swap, it only takes a couple of seconds, and spilled fuel was never more than a pint. In both cases, there was about 1.5" head of fuel above the plug.


IMHO: Being able to frequently draw water/junk from the tank bottoms is by far the most effective solution to clean filters and clean fuel.

The answers seems pretty simple, if you have, or can get a shop vac use it. No big deal to block the tanks vent with some tape. And then stick some oil sorb pads in a pan under the fitting while you put in the valve. Best of both worlds and you're done with it.

If you do, close the crossover shutoff valves to prevent the other tank's pressures and vents from affecting your operation.

UPDATE.

Thanks to all that helped me with this. I installed the shut-off valves on each tank today. Each tank holds 300 gallons and I had about 80 gallons in each tank.

I first taped off the vent and closed all the valves. I have this cheapo shopvac that I use mainly to dewater hard to get at places on the boat such as when I change the engine pencil zincs. A helper put the vacuum nozzle down the fuel fill fitting and wrapped a rag around it to seal it off. We turn it on for about 3- 4 minutes and I removed the plug on the fitting. What I observed is that as the plug was loosen I could hear air rushing into the tank from around the fitting. I removed the fitting and not a drop of diesel come out, not a drop.

Installing the new shut-off valve was a simple matter after I have spent days stressing over this. Thanks again.

WTG!! I was wondering how this turned out, Ron. Kudos to you and crew.

Great info for future reference.

I love a great idea properly executed!!


Forky
1983 Present 42 Sundeck
Twin Lehman 135's

Awesome!!