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Best-Way to Convert an Air Tank... Into a "Slop" T

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Best-Way to Convert an Air Tank... Into a "Slop" T

Unread postAuthor: mark.f » Sun Jan 27, 2008 1:57 pm

Alright, here's the run-down.

I need around 10-15 gallons, (over 35,000 milliliters), of volume, rated to up to at least 50 PSI, which can hold both air AND water.

The simplest way I could think of to do this would be to modify a small 10 gallon carry tank. There are several reasons for this:

1.) Simple, conventional hook-up. Have a 1/2" NPT tank fitting welded to the tank, making it easy to connect my "various hardware" and prepare the tank for water operation.

2.) Specialized tanks are expensive. A carry tanks runs anywhere from 20-30 bucks, and can "easily", (hopefully), be modified to hold water and air.

Here's my problem. The tanks are steel. Pretty corrosion resistant when used with normal air and drained periodically, but not good if I want to be pumping water into one.

My two ideas for solving this problem are outlined below. Please don't post suggestions telling me to "jusst git a stanless tank ther beter!". If you have another idea to water-proof the inside of a standard steel carry tank, post em below.

Idea one is to install a rubber bladder. The material would probably be nitrile rubber sheet about 1/32-1/16" thick, and glued together with rubber cement. The procedure I have to install it is straightforward. Push it through the 1/2" threaded hole until it touches the bottom, lay some plastic over the threads in the tank fitting, lube the hole up, and inject compressed air into the bladder to expand to the size of the tank. Some epoxy or other glue could be used on the outside of the bladder as well to make sure it stays in place. After this, all the installation parts will be removed, and the rubber can be cut to a "spout", which will be glued into whatever fitting I use to connect to my "hardware".

I really like the above idea. It's simple and it should last as long or longer than the rating already imposed on the tank.

The second idea is to spray in some sort of lining. This would have to be done with a rather liquid application process, and I really don't like it. There's too much a chance the lining will miss a spot, allowing rust.

Any other ideas? Right now my money's on the bladder design. I would also have to inspect the tank periodically, because the bladder may "sweat" as cold water is pumped into it. Our water is pumped from a well, so it is both high-pressure and cold, (100 PSIG and around 50-60 degrees in the summer).

Also, this actually does pertain directly to spudguns. Some older members probably know what I'm building, but nobody else ask, because I hate giving stuff away. :wink:
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Unread postAuthor: DYI » Sun Jan 27, 2008 2:24 pm

The rubber bladder idea sounds pretty good. It might get wrinkled a bit, but the pressure inside should help it expand to fit the chamber. Now you just need to find the right kind of glue. Epoxy is probably your best bet, but it's going to be kind of messy no matter what you use.

And I know what you're building, but surely you can use more than 50 psi?
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Unread postAuthor: Ragnarok » Sun Jan 27, 2008 2:31 pm

I assume this is for a 2nd gen, based on what you need it for, and what you say about the "older members" - I'm a bit surprised the idea didn't catch on better than it has.

I like the rubber idea the better of the two you have, but it may be a bit difficult to get to work.

My money would be on a sacrificial zinc or magnesium anode. If you can fit one inside the tank so that it sits in or below the water level, the electron flow will erode the anode in preference to steel - it's common enough on boats and ships.

It doesn't specifically waterproof the tank, but it will prevent the damage to the tank. It's a very well documented phenomenon.

Assuming this is a 2nd gen tank, you won't need it full of water except for a few minutes at a time, so I'm not even sure you'll need to be too concerned about corrosion. Steel isn't that affected by it. Things can sit out in the rain for years and still survive. If you're just filling it with water for an hour or two a week, and draining it out carefully, I reckon the tank will probably still be perfectly capable of taking the compression pressures safely in a decade from now.
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Last edited by Ragnarok on Sun Jan 27, 2008 2:32 pm, edited 1 time in total.
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Unread postAuthor: SpudBlaster15 » Sun Jan 27, 2008 2:32 pm

I'd suggest using a sacrificial anode made of magnesium on the inside of the tank. This is the method employed to protect the hulls of steel ships from corrosion, and should work well for your purpose as well.

Edit: Damn it Rag, you beat me to it.
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Unread postAuthor: Ragnarok » Sun Jan 27, 2008 2:37 pm

@SB15: You've just been post ninja'd!

Ok... I think I need sleep. I should clear the junk off my bed and make use of it.
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Unread postAuthor: mark.f » Sun Jan 27, 2008 2:53 pm

Yes, but aren't those hulls painted as well? I don't think they would make ships with bare steel hulls.

I guess since Ragnarok already said it, it is a Generation II tank. I was originally thinking of making it from PVC, but even with 6" PVC, it would take a tank around 48" long to even get just three 4x shots from it. So, I went to the carry tank.

I still think I'm gonna go with the bladder. I think Home Depot has sheet rubber. A little rubber cement and planning should give me a good, leak-proof lining. If the mythbusters could make a balloon out of lead foil and cellophane tape, I can make a rubber bladder.
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Unread postAuthor: potatoflinger » Sun Jan 27, 2008 3:17 pm

Why not use liquid truck bed liner? as long as you don't miss a spot, it should work very well.
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Unread postAuthor: mark.f » Sun Jan 27, 2008 6:23 pm

Because bed liner is usually pretty viscous. The only stuff I've seen that was thin enough to work was a two-coat epoxy-based formula meant to be sprayed in with a compressed-air gun.
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Unread postAuthor: sjog » Fri Feb 01, 2008 10:58 pm

Fiberglass pressure tank? <a href="http://www.keypure.com/products.asp?cat=19&gclid=CLid6IPNpJECFQRxHgodtG-bWw">link</a>
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Unread postAuthor: mark.f » Sat Feb 02, 2008 9:30 am

200 dollars? *inserts link to bank account*

:wink:
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Unread postAuthor: Gippeto » Sat Feb 02, 2008 9:49 am

There is a product used to seal gasoline tanks that you might consider. It is a liquid, you pour it in and roll the tank around to coat the inside. Then pour out the excess. It works on gas tanks very well. There are several "brands", so check with you local motorcylce shops, and/or auto parts stores.
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Unread postAuthor: grumpy » Sat Feb 02, 2008 9:52 am

could you use an old hot water tank, they have glass liners inside them?
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