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Old 12-02-2022, 08:22   #1
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Sealant for new water tank inspection ports

Hi! Replacing the old aluminum inspection ports on my aluminum water tanks with a Beckson screw out deck plate so I can remove annually to clean and inspect water tanks and make winterizing easier.

Anyone do this? To seal these new plastic deck plates to aluminum tanks any recommendations? Iím a big fan of butyl for most deck fittings.
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Old 12-02-2022, 13:30   #2
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Re: Sealant for new water tank inspection ports

As long as the tank surface is flat I've had excellent results using 0-rings, sized so that the ring fits inside the mounting bolts. O-rings of any sizecan be made by cutting bulk O-ring stock to the desired length and glueing the ends with a special adhesive made for this purpose. Although they are typically placed in grooves, I've found that, so long as pressures are not high, they work very will sandwiched between two flat surfaces.
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Old 12-02-2022, 13:44   #3
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Re: Sealant for new water tank inspection ports

Are you going to through bolt the rims to the tanks? In that case, butyl tape will be fine - just don't leave a route for water to get out and small critters get in. If you are going to glue them in place, figuring that the torque applied when opening and closing the ports is not great, then rough the surface of the aluminum with some coarse sandpaper and glue with something permanent like 3M 5200.
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Old 13-02-2022, 05:56   #4
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Re: Sealant for new water tank inspection ports

We always clean aluminum twice before welds or adhesives. Wipe once before sanding or scrubbing with a stainless brush with acetone. Wipe again with acetone after scrubbing. Move along quickly to weld or adhesive.
The first wipe prevents grinding stuff into the aluminum.
The second removes more dirt, oils aluminum oxide...stuff.
If you use a stainless brush, mark it alu and donít use it on anything else.
Time is your enemy. Aluminum begins to self protect within minutes.
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Old 13-02-2022, 06:09   #5
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Re: Sealant for new water tank inspection ports

Quote:
Originally Posted by Pauls View Post
O-rings of any sizecan be made by cutting bulk O-ring stock to the desired length and glueing the ends with a special adhesive made for this purpose.
Good that you do say "bulk O-ring stock" and "special adhesive made for this purpose", both of which are, or at least used to be critical.

Way back...30, 40 years... a mechanic tried gluing a stock O-ring that had been cut to a smaller size, and even with that special glue, the bond failed.

So at least back then, the O-ring material to be glued is important. No short cuts!
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Old 13-02-2022, 07:02   #6
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Re: Sealant for new water tank inspection ports

Butyl is a good bet.

Perhaps the most important thing is that the hatches are on the center line, and as well centered fore-aft as possible. You want to avoid water slamming against them from underneath, whatever the seal. on tank trucks, the bad failures are always the for and aft hatches, which are subjected to slams when the truck brakes or accelerates.

I wouldn't use an o-ring unless it is specifically designed for them (groove) and it comes with one. They are fussy to glue, through I have done just that many times in refinery settings.


Another simple choice is a 4" NPT floor flange with pipe plug. It won't leak, but there is less room to work.

The hatch will leak some if their is water against it. Screw ports are never that tight. But it is just tap water and it will be very little. Keep the hatches in the center and do not fill it 100%.



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Old 13-02-2022, 07:14   #7
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Re: Sealant for new water tank inspection ports

the seabuilt access plates worked good for me .. water or fuel.

https://www.seabuilt.com/
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Old 13-02-2022, 08:46   #8
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Re: Sealant for new water tank inspection ports

If you want to use an 'O' ring, why not just buy a large diameter to the size you want and have done with it. No need to try and make one up to size, there are plenty of suppliers here in UK and I am sure in the USA who make large diameter 'O' rings and also offer a bespoke service with no minimum order from most of them.
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Old 13-02-2022, 09:17   #9
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Re: Sealant for new water tank inspection ports

I don't see the point of using an o-ring here,when butyl tape supplies a much larger mating surface.

If surge is a problem consider baffle balls. I have them in two 300 gallon fuel tanks which came with no internal baffling.
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Old 13-02-2022, 10:21   #10
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Re: Sealant for new water tank inspection ports

Just did this on my fiberglass, bow fresh water tank. Installed 4" Beckson plate, the clear one. Six small bolts with nuts (in the interior of the tank) to secure plate. used butyl tape on each bolt and around lip of the plate that sits on the exterior, top of the tank. Have yet to test water tightness of seal during some heavy weather.
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Old 13-02-2022, 10:30   #11
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Re: Sealant for new water tank inspection ports

I wouldn't use O rings with a plastic deck plate. Orings are actually pretty solid/hard. They dont squeeze that well. The deck plate will flex between screws.
Personally, on a water tank with plastic deck plate, I'd use Aquarium Safe Silicone sealant.
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Old 13-02-2022, 15:05   #12
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Re: Replacement of steel plates for either diesel

If one wants to replace a ss plate with a (lets say for example) a lexan 5/8" plate on a diesel tank, would the diesel affect the lexan? Or any other problems that could be forseen.

Another question similar to the above would be concerning a water tank access plate replaced with a lexan 5/8" plate, would their be an affecct between the ss tank and lexan? Cracking/sealant?
Ideas on this would be appreciated.
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Old 13-02-2022, 18:01   #13
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Re: Sealant for new water tank inspection ports

Some years back I got almost a foot long vertical crack in the toilet tank. Being a poor grad student back then I improvised a hardware store bought silicon bead patch and forgot all about it. Some years later, when moving out of that apartment, I realized and was very surprised that the tank was still watertight at that crack.

Admittedly no flexing of that porcelain tank over the years but still - a good seal is a good seal.
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