Changing Fittings on a Full Tank ?

[twistedtree]

Originally Posted by David_Old_Jersey

I was going to say what's wrong with pumping the tank out - but then I saw your boat description! My guess is that a lot of fuel is involved!

How about selling the fuel to someone on your dock - or even borrowing there empty / half empty tank(s) - even if you don't get rid of all of it might make what's left manageable to decant?

Anyway, just an idea.

Yes, the boat is a motor cruiser and has two 300 gal fuel tanks with a balancing line between them (which can be shut off). At $4.00 per gallon, I don't want to just give the fuel away - I want to put it right back in the boat when I'm done. Putting 300g into 55g drums would take 6 drums. That's how my yard does it, but they don't think they have that many drums around, and their pump is slow. One thread I'm working is to see if they can come up with anything better. Maybe more drums, maybe a bigger pump, maybe both. Even using heating oil tanks I'd need a tank plus a drum. If pumping out it the only way to do this then I'll figure something out.

[David_Old_Jersey]

Originally Posted by twistedtree

Yes, the boat is a motor cruiser and has two 300 gal fuel tanks with a balancing line between them (which can be shut off). At $4.00 per gallon, I don't want to just give the fuel away - I want to put it right back in the boat when I'm done. Putting 300g into 55g drums would take 6 drums. That's how my yard does it, but they don't think they have that many drums around, and their pump is slow. One thread I'm working is to see if they can come up with anything better. Maybe more drums, maybe a bigger pump, maybe both. Even using heating oil tanks I'd need a tank plus a drum. If pumping out it the only way to do this then I'll figure something out.

Given that you are only adding sensors (and not fixing a leak) then I would run one tank down, and then decant what is left into the other tank or a drum (and do one tank at a time).

The advantage is that it involves doing SFA now - my speciality , but I appreciate that others do like to take a different approach .

[twistedtree]

Originally Posted by David_Old_Jersey

Given that you are only adding sensors (and not fixing a leak) then I would run one tank down, and then decant what is left into the other tank or a drum (and do one tank at a time).

The advantage is that it involves doing SFA now - my speciality , but I appreciate that others do like to take a different approach .

"SFA"? Sounds like something I'd like?

[Wotname]

Originally Posted by twistedtree

No, you are absolutely correct, and it's a possibility. I'd have to add a second shut off after the existing one so I can still have the same fuel management capabilities without shutting out the pressure sender. Also, given the specifics of how the boat is set up, I would need to have two new fuel lines made up. They are essentially hydraulic lines with hydraulic fittings crimped on the ends and are pretty pricey.

I also wonder how much pressure drop will be created by the fuel circulating through the lines while the engine is running, and whether that will mess up the gauge readings in any appreciable way. I don't have the tools or knowledge to calculate localized pressure drops of liquid flowing in a pipe to really answer the question.

And last, I think having the senders in the main fuel line makes maintenance harder, requiring at least one engine to be shut down, and possibly inducing enough air into the system to require bleeding. And in the worst case of a sender leak, it would take out an engine and possibly the generator too. With the senders on a tap separate from the fuel lines, maintenance is easier and can be done without any impact to normal operation of the boat.

So, it's certainly a possibility, but as you can tell I'm leaning strongly towards the approach that creates the best end-product, even if building it is harder.

Ah... the joys of best practice design Looks like you might be draining at least one tank - I trust it will all turn out well.

[GRIT]

Let's not be silly about exploding diesel.

Assuming the fumes are not hot, you will find it very difficult to ignite them with a spark, or flame. Diesel is not volatile like Gas is, that's why we prefer diesel on boats.

Secondly, the sparks you see from the motor are exposed to atmospheric pressure, they are not exposed to the vacuum side of things and will not be exposed to fumes that are concentrated enough to ignite. Assuming you are in the room, and breathing the same air to which the sparks are exposed, you won't cause an explosion. There will be fumes coming out of the exhaust side of your vacuum, but they are extremely unlikely to ignite without being heated.

Diesel will only explode under very special circumstances.

Now, since you may be an American. (No insult intended) I am obliged to say that I take no responsibility for your actions, and do not recommend any action on your part. The information given here is for educational purposes only.

I'd be interested to know if a vacuum would stop a leak as you describe, and will try it myself as an experiment. I'd be careful of not collapsing the tank, even at low vacuum.

Cheers.
Paul.

[GRIT]

I've fallen behind. A pressure sensor sensitive enough to show your tank being emptied will certainly notice when you're taking fuel from the line. When the engine runs you'll have inaccurate readings if you have the sensor in the feed line.
Cheers.
Paul.

[James S]

Stupid idea #156...if your threads in the tank are a fitting welded to the tank then it may be that the threads pass all the way through the fitting...if you tank is shallow enough and if you have an inspection port close enough...it may be possible to screw a plug in the back/tank side of the fitting to stop the flow before removing the outside plug.....Of if not threaded all the way...can you insert a plug...Yes you'll have diesel fuel up to your arm pits twice....but hey!!

[James S]

Stupid idea #157...Install a tee after the shut off valve with a riser higher than the top of you tank....install the sending unit inside the riser.
You still need the second valve.

[s/v Jedi]

Also have a good look at which thread sealant will be used. Not many are diesel rated.

I have used the hard setting Permatex (brown, #1 I think it is) and the expensive hydraulic rated Permatex thread sealant with good results.

Don't use teflon tape as most are not rated for diesel and hard to tell which are.

I waited for one tank to be empty when I took the plug out of the sumps...

ciao!
Nick.