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Old 09-06-2022, 22:43   #1
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How to make gasket for large inspection hatch in water tank

Our two water tanks are made of welded aluminium, 4mm thick
The inspection hatches are 5 mm thick alumnium, 27" square, held by 1/4" bolts 2" apart
How to make a gasket?

Rubber (or rubber-like) sheet is one possibility, but is hard to find and expensive. What thickness and Durometer would you experts recommend? We had 3/16" rubber gasket, which leaked. Last time, used Sikaflex on one tank, which worked but is a PITA to get off

I recall seeing a gasket formed with teflon (or similar) "string" about 1/8" diameter laid along the bolts, making one circle around each bold. Anyone know how it would work and where to buy it?

Another idea is to greases both the cover and tank top, and use Sikaflex or something less sticky. What stuff?

Any other ideas?
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Old 10-06-2022, 04:22   #2
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Re: How to make gasket for large inspection hatch in water tank

i wound't use grease around a water tank..


how about a rope gasket or PTFE gasket tape.. or some self adhesive neprene tape/gasket material
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Old 10-06-2022, 06:24   #3
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Re: How to make gasket for large inspection hatch in water tank

There are PTFE tapes and cords that are designed as to be used as gaskets and they work very, very well…. But if you think rubber gasket material is expensive… you ain’t seen nothing yet.

About 1980 I used this stuff when I was wrenching in a chemical plant. 30 years ago we called it “buck-a-foot” because that is what it cost. Last I looked these days it runs about $3 or $4 per linear foot.

Saying you used “Sikaflex” actually tells us nothing. Sikaflex is a brand, and there are dozens of different kinds of product from pure silicone, to polyurethane, to polysulfide…

There are a lot of products sold as “liquid gaskets” that will work in this application. Be sure to pick one that is suitable for potable water contact, and follow directions. Still more of a PITA to remove than plain rubber, but easier and cheaper up front. Pick your poison.
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Old 10-06-2022, 06:30   #4
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Re: How to make gasket for large inspection hatch in water tank

I suggest neoprene foam tape, such as this:

https://www.amazon.com/Neoprene-Dual...xpY2s9dHJ1ZQ==

That's 1/16" tape, which should work if the joint is flat. If not, then step up to 1/8" tape of the same sort.

Good luck with it.
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Old 10-06-2022, 06:53   #5
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Re: How to make gasket for large inspection hatch in water tank

We have the same type tanks, and covers; ours are sealed with a full-size cork gasket approx 3/16" thick. Every time I remove the cover I'm in fear of that cork tearing....so far it has not, but I'm sure one of these times it will! I carry a sheet of cork and a small ball pein hammer so I can make a new one when I need to. Had never thought about using a string of foam gasket around the inside of the bolt pattern as an alternative. following.
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Old 10-06-2022, 07:34   #6
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Re: How to make gasket for large inspection hatch in water tank

A premium silicone product will work if applied correctly. Silicone only seals correctly if used ad a gasket by applying a thick amount, 1/8 to 3/16 and allowed to cure then compressed after its dry. Put silicone about 1/2” wide by 3/16 thick. Use shims 1/8 in the outer edges of the cover, lightly bolt down cover on to shims and let cure 24 hrs. Remove shims and tighten as usual. Done it dozens of times. Good luck.
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Old 10-06-2022, 07:49   #7
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Re: How to make gasket for large inspection hatch in water tank

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Originally Posted by captmob View Post
A premium silicone product will work if applied correctly. Silicone only seals correctly if used ad a gasket by applying a thick amount, 1/8 to 3/16 and allowed to cure then compressed after its dry. Put silicone about 1/2” wide by 3/16 thick. Use shims 1/8 in the outer edges of the cover, lightly bolt down cover on to shims and let cure 24 hrs. Remove shims and tighten as usual. Done it dozens of times. Good luck.
I will add to this description- wax the lid- or spray with PAM. Then follow above with a high quality silicone sealant and set lid on top- be sure to include around bolt holes- then after 24-36 hours bolt it down. This makes it removable any time.
RV gasket maker also works well.
The top being set loose on top makes the gasket liquid flat/level. then when the tightening down process makes the tight seal. With the release agent on the top this is removable multiple times.
caution on silicone-if too thick the silicone will not dry internally- so do not exceed the thickness instructions.
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Old 11-06-2022, 00:33   #8
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Re: How to make gasket for large inspection hatch in water tank

Whilst we are on water - I have a fresh water leak in the system - which I admit is old, but no problems before. I have found two small leaks, have fixed, but there must be a third of which I will be absolutely buggered down a bung hole - that I am unable to find.

Have used the dye trick - how I found the other two - but my pressure water pump is going off for a second every three minutes or so.

Any ideas - sensible ones --

Cheers

Gb
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Old 11-06-2022, 01:13   #9
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Re: How to make gasket for large inspection hatch in water tank

2" apart is to far for 4mm aluminium plate, I'd double the number of bolts and use a medium durometer elastomer gasket at least 1/4" thick.
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Old 11-06-2022, 02:55   #10
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Re: How to make gasket for large inspection hatch in water tank

Quote:
Originally Posted by gbmacca View Post
Whilst we are on water - I have a fresh water leak in the system - which I admit is old, but no problems before. I have found two small leaks, have fixed, but there must be a third of which I will be absolutely buggered down a bung hole - that I am unable to find.

Have used the dye trick - how I found the other two - but my pressure water pump is going off for a second every three minutes or so.

Any ideas - sensible ones --

Cheers

Gb
from your description look downstream from the pump- 1) feel every fitting at the connection and if needed use paper towel to see dampness.
2) if you have hot water- and red tracer hose-look for the area where the hose is connected- I had a regular area where the barb was too short and the hose would swell- eventually bursting. solution was changing barb for longer barb 3) that's a lot of water so I would also look for a failed expansion tank (if you have one 4) shower head valve leaking.
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Old 11-06-2022, 03:00   #11
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Re: How to make gasket for large inspection hatch in water tank

You can get those at an auto parts store.

https://www.summitracing.com/search/...asket-material
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Old 11-06-2022, 04:53   #12
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Re: How to make gasket for large inspection hatch in water tank

McMaster Carr

part 45925K73 $32 for 20 ft.
part 45925K74 $30 for 12 ft. (next size up)

expanded ptfe gasket tape

It has a small strip which you remove to expose and adhesive to set in place. simply overlap at the end. After it compresses the first time you would probably want to replace when opening up for cleaning/inspection. I have used this many times for years working in the chemical industry when other gasket solutions haven't worked due to surface irregularities, including on inspection hatches for tanks. It is FDA compliant for use with foods.
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