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Old 08-15-2016, 07:30 PM   #1
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Aluminum grey water tank?

Background: I am looking to add a grey water tank (under floor/between frame rails) to a 1964 Bambi II with frame rails only 3.5" deep (All Bambi frames were made of lighter/smaller steel rails).

VTS offers a grey water tank that "could" work...but it will be a bit too deep necessitating the fabrication of a drop pan to cover the tank. No real big deal, but...

I have access to a metal shop that could likely fabricate an aluminum tank custom fit to the frame cavity that would fit inside the original belly pan. I was thinking that having aluminum pipe welded on in all the right places for vent, inlet, and outlet, those could be connected to PVC plumbing with rubber connectors.

Is aluminum an acceptable material for gray water tanks? I can't see why it wouldn't be, but one never knows. BTW, the original fiberglass black water tank will be put to use.
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Old 08-16-2016, 07:40 AM   #2
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Aluminum would be fine, but cost would be a deciding factor for me. Have you looked into a custom size plastic tank?
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Old 08-16-2016, 08:20 AM   #3
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Aluminum would be fine, but cost would be a deciding factor for me. Have you looked into a custom size plastic tank?
Cost will likely be free or close to it, and free student labor. They have to learn how to tig weld somehow. Live projects are good for the students and give them a fine sense of accomplishment.

Thanks for the words...much appreciated!
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Old 08-16-2016, 09:17 AM   #4
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Aluminum should work fine in a gray tank application. Given a choice I personally would lean towards a 3003 or 5052 series material, these alloys are easily formed, welded and have good corrosion protection characteristics.

Make sure you snoop, or soap bubble test the completed tank (using a very low pressure) to check for leaks prior to installation.
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Old 08-16-2016, 09:19 AM   #5
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Originally Posted by PA BAMBI II View Post

Is aluminum an acceptable material for gray water tanks? I can't see why it wouldn't be, but one never knows. BTW, the original fiberglass black water tank will be put to use.
My cruising sailboat had an aluminum black water tank (grey water goes overboard on a sailboat) that lasted over thirty years. eventually a small pin hole developed from rubbing against a some debris underneath it. I was easily patched. Aluminum would be much lighter and would work really well.
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Old 08-16-2016, 03:01 PM   #6
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You could line the tank with rubber "sloshing compound" and guarantee no leaks or corrosion. I used stainless when I made the waste tanks for my trailer. When I leak tested them I used the absolute lowest pressure my regulator would let air through at, about 1/2 psi. The tanks blew up like balloons and stayed that way costing me 2" of ground clearance which blew my carefully measured plans! If you leak test with air you might want to use a vacuum cleaner on blow or some other very low pressure air source. Even a vacuum on blow might stretch the tank a bit so be careful! A store bought plastic tank that hangs down below the frame might be a good thing for plumbing the drain and valve?
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Old 08-16-2016, 03:31 PM   #7
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Cost will likely be free or close to it, and free student labor. They have to learn how to tig weld somehow. Live projects are good for the students and give them a fine sense of accomplishment.

Thanks for the words...much appreciated!
Jealous, oh so jealous! Aluminum is fairly cheap right now too, there's a glut of the stuff.
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Old 08-16-2016, 06:48 PM   #8
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Quote:
Originally Posted by Kevin245 View Post
Aluminum should work fine in a gray tank application. Given a choice I personally would lean towards a 3003 or 5052 series material, these alloys are easily formed, welded and have good corrosion protection characteristics.

Make sure you snoop, or soap bubble test the completed tank (using a very low pressure) to check for leaks prior to installation.
Thank you. Please tell me more about the soap/leak test.

I will have this made at the technical high school where I work...and the welding teacher is amazing and has been doing it a long time. I know he has made tanks before as I have seen them over the years.

How can I help direct them with the leak test? And how do you seal up the inlet/outlet/vent tube for the leak test?

Thanks again!! Ben
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Old 08-17-2016, 01:42 PM   #9
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Thank you. Please tell me more about the soap/leak test.

I will have this made at the technical high school where I work...and the welding teacher is amazing and has been doing it a long time. I know he has made tanks before as I have seen them over the years.

How can I help direct them with the leak test? And how do you seal up the inlet/outlet/vent tube for the leak test?

Thanks again!! Ben
Leak testing a tank in this instance involves pressurization of the component, in this case, compressed air, then applying a soapy solution on the weld seams. The key is to have enough pressure applied to force air through pinholes or other discontinuities in the weld and adjacent areas. The soapy water or Snoop is then sprayed on the test areas while the component is pressurized while you watch for bubbles to repeatedly form.

Cylindrical tanks with dished or hemispherical heads typically withstand higher pressures than box style tanks. Given that your tank will likely be rectangular in shape you will be limited to a very low pressure application, likely in the 0.5 to 2 psi range depending on material properties and tank configuration. This is usually more than enough of a pressure differential to create an effective test environment without causing the tank to bloat on you, but design parameters will dictate how much pressure can be introduced. Just remember that you are compressing air so keep the pressure low as there is a tremendous amount of stored energy when gases get compressed. Even at low pressures things can fail catastrophically.

There is a poorly recorded video on YouTube that shows the basic concept of leak testing though I would take his approach with a grain of salt. I would add a reliable pressure gauge and a pressure relief device into his approach, also I would apply the soapy water with spray bottle.

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