Solution To Leak In 4" Threaded Connection

[webmonk]

I have a fiberglass tank that has a 4" threaded plastic opening on the bottom (Pic #1). There is a corresponding adapter fitting that screws in and has a rubber gasket (Pic #2). The tank holds about 150 gallons of water. One day it sprung a leak when the rubber gasket bulged out (Pic #3).

I have been hesitant to put the tank back in service for fear of a repeat problem. So, I'll turn to some experts for some answers to my questions.

A) Why is the possible reason for the leak? Was the adapter not screwed in tight enough?

B) What steps can I take to prevent this from happening again?
B1) Should I add some sort of adhesive (similar to PVC cement)?
B2) Would a thick Teflon tape be advisable? Would it even work with the deeper threaded connection?
B3) Should I just use a new rubber gasket and try again? If so, how do I know how tight to make it?
B4) Both B2 and B3?
B5) Something completely different?

Thanks in advance for any advice.

Picture #1

Tank connection

• webmonk
• May 24, 2018

Picture #2

Adapter with gasket

• webmonk
• May 24, 2018

Picture #3

Lead due to bulging gasket

• webmonk
• May 24, 2018

 

[breplum]

Image not showing up.

 

[webmonk]

Sorry, did not know how embedding images worked. They showed up initially. I figured it out. Thanks

 

[CT18]

Try some plumbers grease on that o ring

 

[johnjh2o]

Try some plumbers grease on that o ring

I agree, but don't over tighten.

 

[webmonk]

Thank you for the replies. There seem to be a consensus thus far that plumbers grease (which I was not aware) is the option to choose.

Pardon my ignorance in this matter, but how does silicone lubricant on the o ring prevent a leak on a tank where it previously leaked? To try and educate myself I did some quick searching online about the grease and found someone state that "Silicon grease is only for lubrication purposes where there is already a water tight seal." My vision of grease is that it lubricates and doesn't seal. Please help educate me.

The ring seems to have some sort of substance on it already, which would of course be that it was grease. I know there are a lot of unknowns here since nobody knows how much was applied, if it was over tightened, or if there was a flaw in the ring or connection parts. I'm just leery of having 150 gallons of water spraying out in my basement again. Hope you understand my wanting to make sure before I fill it up with water again.

 

[Mr_David]

Can't see the detail of the tank fitting. is the o-ring the manufactures design.
Usually when an o-ring is used, there is a grove that is designed to retain that o-ring to prevent it from popping out.
The lubrication, in some application, is to prevent the o-ring from sticking to the component that is moving across the surface of the o-ring( like a cap or a plug being screwed in or onto)
and causing it bind up at get pushed out of the grove that it was intended to stay in.
Any lubricant on the o-ring is just to minimize friction
In your case, if the surface of the tank fitting is flat, with no grove to retain the o-ring then the pressure from the screwed in cap/plug may have squirted the o-ring out, and not the pressure exerted by the volume of water behind the cap.
If the o-ring is the correct way it was to be sealed adding Teflon tape could compromise/foul the seal of the 0-ring as you turn it in.
I would try a new o-ring first.
Plug is plastic so they can also be easily distorted and cause o-ring failure.

https://www.google.com/search?q=o-r...m6LbAhUMXKwKHQyGCW0Q_AUICygC&biw=1680&bih=887

 

[Diehard]

As questioned by Mr_David, "is the o-ring the manufactures design."?
Doesn't seem like a good application for an o-ring. My first thought was that it would be a flat rubber washer.
Teflon tape on the threads wouldn't hurt either.

EDIT: I would assume that if the water pressure was only the head of water in the tank, an o-ring would work but must not be over tighten causing the distortion as shown in the picture.
On the other hand, if the tank is within a pressurized water system, as in a water service or the like, then a tight connection should be made and a flat washer used, as mentioned above.

 

[breplum]

Overall you quite possibly have a poorly designed tank threaded tap.
The Female tank tap may be a running thread and not a tapered thread.

If it were a tapered thread, then Teflon tape should make a good seal and not require the O-ring (I concur with Diehard's comment).
Having an O-ring like shown, under pressure is a sure fire recipe for failure as readily shown in your nice picture.
Side note, if that is the bottom of the tank, then put a tee with a hose bibb or lever handle valve in there and provide a way to drain the tank!

 

[webmonk]

As questioned by Mr_David, "is the o-ring the manufactures design."?

Yes. The Everything in the pictures is the manufacturer's design.

The Female tank tap may be a running thread and not a tapered thread.

I'm not an expert on threads. Here are some up close pics. Let me know if they provide the level of detail needed to identify the thread type.

Adapter Threads

• webmonk
• May 26, 2018

Fitting Threads

• webmonk
• May 26, 2018

Here is a further close up pic of the of the adapter partially connected and the positioning of the o ring. You can see the where it sits in the picture above, where it has been removed.

Adapter Partially In Fitting

• webmonk
• May 26, 2018

Side note, if that is the bottom of the tank, then put a tee with a hose bibb or lever handle valve in there and provide a way to drain the tank!

Already have a setup similar to what you suggested. It is not a tee, but it provides a valve and drain point.

Completed Tank Setup With Drain Pipe

• webmonk
• May 26, 2018

 

[Mr_David]

Now you can see the grove in the tank fitting.
That o-ring should have not popped out like that.
Re install it with some silicone grease and just be care it does not bind up and pop out.
You should be able to screw the plug in until the hex flange is flush with the tank fitting ,leaving no room for the o-ring to pop out

 

[breplum]

It does not seem to be tapered threads. Tapered threads use more than 11 threads. Plastic tapered thread assemblies are prone to cracking so it makes sense that the o-ring is the sealing element. A lame sealing element, but that's what you have to work with.

Without full capture in the design of those fittings, it is a delicate balance to get it to seal and not pop out.
The mfr. has failed in the design/execution of these fittings and you are stuck.

As a plumbing contractor, we would never get involved with tank fittings like that because it is a invitation for failure, and too much liability.
So, good luck.