Pump outlet connection persistent leaking very slowly

[miamicuse]

I have a pump with a leak at the outlet where it connects to a 2" PVC male adapter.





In order to fix the leak I did some reconfiguration - raised the pump, added in two unions. and remade the threaded connection.



I did the threaded connections using RectorSeal T Plus 2 pipe thread sealant. No leak after that...or so I thought.

Today I fired up the pump and after it primed, I observed no leak. An hour later I came back and I saw a slow leak at the outlet again. Same exact spot.

Since I have added two unions, I took them apart and I noticed the male adapter was not TIGHT-TIGHT into the housing. I knew I hand tight that connection, then used a pipe wrench to go one more full revolution. Now it is a bit loose. Hmmm, I suppose the vibration and movement of the pump worked the connection loose?

In the reconfigured plumbing, I have three threaded joints, one between the suction side manifold and the union (#1), one at the inlet of the pump (#2), and one at the outlet of the pump (#3). They were all made the same way, yet only the outlet side is leaking. Of course the other two are being subjected to negative pressure, while the outlet connection is subjected to positive pressure.



After I took apart the unions, I remove the male adapter, cleaned both the female connection at the pump and the male adapter real well, and used MEGAMAX tape instead.







Then I remake the connection, I am close to "bottoming out" the male adapter into the housing connection, started the pump, and it leaked again, very slowly.

Any idea what else to try? Use pipe sealant on the male adapter PLUS tape over it? Use more wraps of the tape?

Could the vibration of the pump cause the female threaded connection to deform so that a watertight connection is no longer possible?

[Denniswiseman]

If you are close to bottoming, you may not have enough tape to form a thread seal
I would be inclined to wrap more tape and then put some silicone round it. Leave it overnight to harden before putting water and pressure
I doubt that vibration would deform either of the two threads
You don't have a cracked female thread asit seems strange that it was leaking before and still is with new unions

[miamicuse]

If you are close to bottoming, you may not have enough tape to form a thread seal
I would be inclined to wrap more tape and then put some silicone round it. Leave it overnight to harden before putting water and pressure
I doubt that vibration would deform either of the two threads
You don't have a cracked female thread asit seems strange that it was leaking before and still is with new unions

I don't think the female threaded connection has cracked.

The first repair attempt I cut the pipe between the pump outlet and filter. Once I cut it I was expecting some resistance to unwind the male adapter, not so, it was very loose. But this time I made it hand tight plus one full revolution and it still leak.

[Teapot]

It is usually because of two parallel threads being used. If the male thread of your union was tapered it would find a point to bind and therefore seal.
Try forming a taper by using more tape towards the top of the thread than you use at the front. Back this up with a modified polymer sealant or Oase pond sealant rather than silicon which is a bit thin.

[miamicuse]

It is usually because of two parallel threads being used. If the male thread of your union was tapered it would find a point to bind and therefore seal.
Try forming a taper by using more tape towards the top of the thread than you use at the front. Back this up with a modified polymer sealant or Oase pond sealant rather than silicon which is a bit thin.

I will try more tape first. Basically put more wraps/turns on the rear of the male threads then the front? I always worried if I do that I may cross thread and not know it and end up mutilating both the male and female ends.

If that doesn't work, put sealant over the tape? Would the pipe thread sealant I currently use work in this case? The one I have is the RectorSeal T Plus 2:

RectorSeal® T Plus 2® pipe thread sealant is a non-setting, multi-purpose compound which contains PTFE, plus synthetic fibers to create a stronger seal. Recommended for use on threaded galvanized steel, iron, brass, copper, aluminum, stainless steel, polyethylene, fiberglass reinforced, PVC, CPVC, and ABS pipe. T Plus 2 may be pressurized immediately following application.

[miamicuse]

I remade the connection again with tape plus pipe sealant.

Once I started the pump no leak. Checked after two hours no leak. Check the next day (after the pump had shutoff and restarted in the morning) I see a slow leak again.

I examined the outlet and there is no crack. But may be the female outlet connection has expanded from perhaps overtorque of the male adapter into it?

Would putting a hose clamp on the outside of the outlet help at all?

Not sure what else to try except silicone? What kind of silicone? 100% pure silicone?

[Teapot]

Back this up with a modified polymer sealant or Oase pond sealant rather than silicon which is a bit thin.

[miamicuse]

Back this up with a modified polymer sealant or Oase pond sealant rather than silicon which is a bit thin.

Thank you Teapot, I thought what I used already, which is RectorSeal T Plus 2 is close to a polymer sealant? May be not. Do you have a specific product you recommend? Is Oase pond sealant something to try? But that's a foam based product, once you put it in can it be taken apart again? Is it a "permanent" thing?

https://www.rectorseal.com/rectorseal-t-plus-2/
RectorSeal® T Plus 2® pipe thread sealant is a non-setting, multi-purpose compound which contains PTFE, plus synthetic fibers to create a stronger seal. Recommended for use on threaded galvanized steel, iron, brass, copper, aluminum, stainless steel, polyethylene, fiberglass reinforced, PVC, CPVC, and ABS pipe. T Plus 2 may be pressurized immediately following application.

[Teapot]

Oase pond sealant over in Europe is a black thick non setting polymer that you can take apart again. Used it successfully on many thread leaks provided they are non pressure spurts. For any pressure type leaks (spurts) sika flex or similar.