stripped thread in Pentair filter shell

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V

vaman

0
Jun 14, 2014
24
Alexandria Virginia
The female thread for the bottom drain plug of my Pentair CCP320 cartridge filter is stripped.
The symptom is that as I turn the plug to tighten it, it clicks and no longer advances.
I bought a new drain plug. Still a leak.
I wrapped the threads with teflon tape. Still a drip.
I went so far as to thread the plug from the inside, hoping that the pressure of the water would work in my favor to press the plug against its O-ring. Still a drip.

I ordered a 1 1/2" x 12 tap to refresh the thread, but I consider this a long shot.
I'm experienced in threading metal but I am pessimistic that a thread in plastic can be restored.

Has anyone a solution to this problem?
 
Nope, but I cleaned my filters today and the same thing happened. I think I got it just snugged up right before it clicked past and it barely had a drip. It started raining and I haven't been out to re-check it. I'll probably put a whole bunch of teflon tape on it if it is still dripping.
 
It's a 1.5" pipe thread (NPT). Try a tapered threaded plug with teflon tape and sealant.

The 1-1/2" x 12 isn't the right thread. Plus, it has to be very expensive. The thread is NPT, which is 11.5 threads per inch.

Worst case, I would consider gluing a 1.5" x 1.25" threaded reducer into the hole and using a 1.25" threaded plug.
 
JamesW said:
It's a 1.5" pipe thread (NPT). Try a tapered threaded plug with teflon tape and sealant.

The 1-1/2" x 12 isn't the right thread. Plus, it has to be very expensive. The thread is NPT, which is 11.5 threads per inch.

Worst case, I would consider gluing a 1.5" x 1.25" threaded reducer into the hole and using a 1.25" threaded plug.
Click to expand...

This is interesting and concerning. I looked carefully at the thread on the male plug and could detect no taper. So I decided it was NF.
But I was unable to get a perfect match to the thread with either a 12 or an 11 thread gauge.
This fits your statement that the thread is 11.5 tpi.

Please don't take issue with this, but are you certain that the thread is NPT? If so, then please tell me if the threaded reducer that you mention is common enough to be available at HD or Lowes.

Many thanks.
 
I'm pretty sure that it's 1.5" NPT. The plug that's made for the drain uses an o-ring, so it does not seal at the threads.

You can verify the thread by taking the plug to a hardware store and trying it in a female 1.5" NPT fitting.

I'm pretty sure that a standard tapered threaded plug with teflon tape and sealant will work. I would try that first.

The threaded adaptor PVC Reducer Bushing 1.5" x 1.25" (MIP x FIP) should be available at a hardware store.

One concern is that there might be a crack at the hole causing the problem. If there is a crack, it's best to replace the filter body.

If there's no crack, then you should be ok.
 
I think that it's NPT/NPS. As you noted, neither the 11 or 12 matches.

Correction: NPT means National Pipe Taper. NPS means National Pipe Straight. They both have the same threading. Either way, I think that it's a national pipe thread.

The threads are not compatible with other thread types as the threads per inch won't match as well as other thread characteristics such as angle of threads.
 

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Mine is barely dripping, hardly enough to leave a wet spot. So, I'm not touching it for now. :)

What are you going to do? Install a bushing? Or reuse the Pentair plug? When I do decide to work on mine in the fall, I hope, I will try pink teflon tape first. It is thicker and sturdier and I'm hoping it will seal earlier so I don't have to tighten it all the way to the o-ring.
 
I just don't know what to do next. I have two Pentair plugs. Neither seals.
I've wrapped them with teflon tape. Still leaks.
I've coated the threads with a non-hardening thread sealant. Still leaks.

I installed the plug from the inside twice. The first time, no leak. The second time, leak.
The company that services my pool has the proper tap.
As a last resort, I might give that a try.
 
You might have a crack in the housing through the threads.

If that's the case, you will need a new filter body.

If there's no crack, try a tapered plug with teflon tape and sealant.

The plug is NPS (National Pipe Straight), it's not designed to seal at the threads. It's designed to seal at the o-ring.

NPT (National Pipe Taper) is designed to seal at the threads.
 
JamesW said:
You might have a crack in the housing through the threads.

If that's the case, you will need a new filter body.

If there's no crack, try a tapered plug with teflon tape and sealant.

The plug is NPS (National Pipe Straight), it's not designed to seal at the threads. It's designed to seal at the o-ring.

NPT (National Pipe Taper) is designed to seal at the threads.
Click to expand...

Now I'm confused. Pentair told me the thread on their plug is NPT. And yet it has an o-ring.
 
The terminology can be confusing and it's not always used consistently.

NPT can mean National Pipe Thread or National Pipe Thread (Tapered).

They probably meant National Pipe Thread.

National Pipe Thread can be straight or tapered. Either way, it's the same thread other than a taper.
 
I caved in and had the pool guy come by today. He took a huge 1 1/2 x 11 1/2 tapered tap from his box, ran it through the thread in the tank, and screwed the plug in until the o-ring seated.
No drip.
I asked about the apparent discrepancy that had me confused; namely, the straight threads on the black plug and the tapered tap he used.

He said that
(1) a tapered tap is necessary to properly start the tap in the threads, and
(2) the wall of the tank is so thin, and therefore the extent of the female thread is so little, that only a short portion of the tap actually cuts. That portion is for all intents and purposes straight.

If I had $235 - the on line cost of that tap - I'd buy one. But I don't. So I'll hope he straightened the threads enough to get me through another couple of dozen insertions of the plug.
 
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