Sealing pipe threads with large gap

[nelsonr]

I have a big blue water filter I'm having a hard time sealing. It has 1" NPT metal and I've got pipe with 1" MPT, also metal. I think the filter is low quality, I'm not finding any brand name on it. There's a large gap between both threads (not tapered) and before I go and buy another filter housing I wanted to see if there's a better way of doing it. So far I've looked into:

1. Rectorseal T Plus 2: leaked horribly.
2. PTFE tape. I have to wrap 10+ times for it to start fitting a bit better: a tiny bit better than T Plus 2.
3. PTFE tape plus Rectorseal T Plus 2: leaked quite a bit.
4. PTFE tape plus Rectorseal No 5: a bit worse than T Plus 2.
   
5. Cotton wicking, PTFE tape, T Plus 2: small leak
6. X-Pando: tiny leak, but I think it cracked when I was putting the filter housing back on
7. Hercules Block: "Safe for potable water" but not NSF 61 compliant which is required in my county.

Is there pipe dope/paste that will not set soft but also be flexible so it doesn't crack? Should I just give up and replace the housing? Everything else is CPVC and plastic tends to seal better so should I switch to it? Any other ideas? Thanks!

P.S. T Plus 2 works well in all other threads I have used it for, both metal and non-metal.

 

[Reach4]

I have a big blue water filter I'm having a hard time sealing. It has 1" NPT metal and I've got pipe with 1" MPT, also metal. I think the filter is low quality, I'm not finding any brand name on it.

I have what I believe to be a genuine Pentek Big Blue housing. I just looked, and there is no name on it however.

The part with the NPT threads is black plastic. I presume your pipe and fittings are cut threads and not some kind of molded metal. I would go for the genuine housing. You have given this one an outstanding effort.

 

[Sponsor]

 

[CountryBumkin]

It has 1" NPT metal and I've got pipe with 1" MPT, also metal. I think the filter is low quality, I'm not finding any brand name on it. There's a large gap between both threads (not tapered)

What do you mean by "there is a large gap between both threads"?
it sounds like you have two different thread types.

Can you post a picture?

This stuff is not that hard - there must be a mismatch of some sort (like "straight thread to tapered thread").

 

[nelsonr]

Sorry for the delay, things got a bit crazy right after I posted. Here are some pictures to show what I'm working with. It's all 1" pipe:

• male.jpg: the MPT to CPVC adapter
• female.jpg: FPT "out" side of the filter housing
• combined.jpg: side view of both MPT and FPT
• loose.jpg: screwed in about 2-3 threads, I took the left picture pulling the pipe up and the right picture pushing it down. You can see I can wiggle it at least half one thread's distance.

 

[nelsonr]

The filter looks very close to this (brass+clear housing+relief valve+wrench, the bracket is slightly different): http://americanwateronline.com/prod...le-pleated-sediment-clear-housing-w-blue-tint

The MPT to CPVC adapter says Legend Valve and is stainless steel like these: http://www.legendvalve.com/images/specsheets/2013417-304StainlessSteelTransitionFit-143259.pdf

 

[nelsonr]

One last thing to note is that to get any decent amount of torque on it the MPT adapter goes up against the plastic surrounding the FPT outlet, so you'll see it's somewhat damaged. If the brass would be at least flush I guess the plastic wouldn't be affected. Maybe that's part of the problem? It still seems to wiggle much more than any other connections I've done in the past.

 

[Dj2]

Before you raise your white flag, try brass connectors instead of the Legend connector nipples. I always use brass connectors or bushings (going into metal or plastic with just tape), and never had problems like yours.

 

[nelsonr]

Before you raise your white flag, try brass connectors instead of the Legend connector nipples. I always use brass connectors or bushings (going into metal or plastic with just tape), and never had problems like yours.

Thanks, I'll give that a try.

 

[Cacher_Chick]

I think the threaded adaptor you are using is too short in the threaded section. You might have better luck threading in a brass nipple on each side of the housing and converting from there.

 

[nelsonr]

I just got some brass adaptors as dj2 suggested and so far it's looking promising! The threaded section is longer (cacher_chick was probably right) and I can get some good torque before running out of threads so it never touches the housing plastic. I need to get a few more parts to put it all together so it will likely take a week or two until I have another update.

Assuming this works I'm curious what the stainless steel connectors are for then. Are you supposed to match metals (SS with SS, brass with brass)? Does SS have less threads since it's stronger? I always thought MPT/FPT was generally universal as long as you matched size + tapered or not.

 

[Craigpump]

You shouldn't combine different metals, but the inserts in the filter head look to me like they're brass so brass nipples would be the right ones to use.

Stainless is harder than brass, so it won't bury into the corresponding thread as far as brass. Because it's harder, it's also tougher to get leak free.

When we do a filter installation we always use a union on both the inlet and outlet.

 

[Reach4]

There can be a problem with stainless to stainless galling. So alternating brass and stainless might have its advantages

https://www.boltdepot.com/fastener-information/Materials-and-Grades/Thread-galling.aspx

 

[nelsonr]

Thanks for all your comments. The brass adaptors tightened nicely and have not leaked at all in over a week. Crisis averted! There are already several unions so it's more modular including the filter inlet/outlet.