Glue PVC threaded fitting; unwise?

[hfmann]

I've already got a lot of threaded fittings for a new closed loop system I'm ready to put together. However, in order to minimize potential leaks, now I've decided I really want to have glued joints instead of threaded in certain areas. Is it stupid to glue threaded fittings together? Or do I really have to get slip fittings?

Some of the places I originally had threaded fittings planned are really hard to get to. If the thread leaked, it'd be almost impossible to get to in order to tighten. Originally I thought it threaded joints would make disassembly and later refinements easier. Now I realize if I couldn't get to them to tighten once put together, I wouldn't be able to loosen them either. duh!

Thanks,
Hal
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[Anonymous]

I have had many leaks with threaded fittings over the years. Generally you can't tighted threaded fittings after all of the pieces are in place.

I have never had a glued fitting leak.

Guess what I'd do?

I only use threaded if I think there is a good chance that I will want to redo the plumbing. Threaded is removable.

Louey

 

[hfmann]

Hey Louie,

Ok. I already spent the money on the threaded fittings and can't take them back at this point. I'm thinking I can just glue AND thread them together. Do you think this would provide the same reliable seal as a regular glued slip fitting?

What'd ya think?

(BTW - that 300g of yours is tremendous. Nice job! Don't know how you had the patience to design and construct it.)

Hal
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[Anonymous]

Thanks Hal. I actually built it on the fly with only a concept in mind. I spent all of 15 minutes drawing up my sump design and I faxed the sketch to glasscages.com. Of course I did spend a few years thinking about the design, I just never wrote anything down.

It was a lot of work though.

I don't think it is advisable to glue threaded fittings. Just put a good three wraps of tape, or use pipe dope. Thread them tight. Some people say don't tighten them all the way, so that you can tighten them some more if they leak. I say than not tightening them just increases the chances that they will leak.

Louey

 

[hfmann]

I'm sure it was a ton of work Louie. But I'm sure you're real pleased with the outcome.

Thanks for the input on the pvc fittings. Unless someone else convinces me gluing the threaded fiittings will work, I'm going to pop for buying the slip ones.

Since I'm going to put the whole thing together and test it away from the tank, I'd have to tape and thread all those fittings, test, and then take apart, remove the tape remnants and then put it back together again on the tank. So even if I get it "leak free" on the test, there's no guarantee I'd get it back together without a drip or salt creep. I see I'm talking myself into the glued fittings.

Thanks again,
Ha
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[Anonymous]

I wouldn't glue them... why? Because there's probably a good chance that the PVC cement will start to bind up before you tighten them all the way!

Use teflon tape and take your time, should be fine.

 

[Rob Top]

I wouldn't glue them... why? Because there's probably a good chance that the PVC cement will start to bind up before you tighten them all the way!

I was going to say that.

Besides the teflon tape doesn't smell as good as the glue and primer 8O

 

[Anonymous]

Ditto sfsup and Rob Top says.

You have many options. One is to test it out, and when you disassemble, do it in such a way that minimum number of joints need to be taken apart, for example.

I change my plumbing so often that if I use slip, I would have spent 10X more on the PVC. If you do it right, there is very little chance that it will leak. You need to have a good design (make it easy to take apart or tighten if leak is found), and test it with pressure by close off all opening and pressurize it to find leak.

I would make use of both slip and thread to get the best of both world. Good use of union and thread joint make it much less costly when you need to alterate the plumbing.

 

[hfmann]

Thanks SF, Rob, and Seven,

Thanks guys, you certainly bring up a lot of good points.

And wouldnÂ’t that have been a kick in the rear? To glue the threaded fitting and have it bind before getting it tightened enough. Glued and leaking! Yikes!

The strategy of mixing threaded and glued makes a lot of sense to me. I originally designed it as almost all threaded in order to provide the ease of frequent modifications. Also I was hoping thereÂ’d be compatibility and interchangeability between unions. But I found that there isnÂ’t a standard between various manufacturers of unions (i.e., one manufacturerÂ’s male union piece doesnÂ’t work with another manufacturerÂ’s female piece.). So in future modifications I think I need to be able to remove the entire union (male and female) and use over again.

Bottom line, I think IÂ’ll glue the sections I wouldnÂ’t be able to get to. And then IÂ’ll use threaded fittings and unions to put those sections together.

Now for some more questions:

1. Pressure testing?

test it with pressure by close off all opening and pressurize it to find leak.

Seven, are you suggesting using air to pressurize and test it?
2. Teflon tape – everyone, including Delbeek, issue emphatic warnings about NOT over-tightening. How do you tell how tight is tight enough but not too much?

And now back to the drawing board.

Hal
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[hfmann]

Oops! forgot to get this included in the list of questions.

Teflon tape - I know to wrap in the direction of the threads, but when folks refer to number of wraps to put on, what exactly do they they mean? For example if they say wrap three times, does that mean to have have three layers of tape on the entire thread section? As I wind tape on, I'm overlapping as I proceed to cover the entire length of the threaded section. I believe TRA3 authors say to use 10-12 "turns" on intake side of pump and 6 on other places. They also caution about putting too much on.

There oughta be video on how to do this stuff! :lol:

Thanks,
Hal
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[ChrisRD]

I agree with the others that trying to glue threaded fittings would be a bad idea.

Here's what Spears has to say about constructing pipe joints:
http://www.spearsmfg.com/howto.htm

 

[hfmann]

Great info Chris,

That sheet from Spears tells exactly how tight to tighten those guys. Thanks.

Now, I'm still not sure what they mean by "wraps of tape". Attached are some pixs I just took that hopefully better explain my confusion.

The one example of having 3 LAYERS of tape covering the entire length of thread may make it way too thick. I imagine if there is too much tape it could cause the pipe to compress or even worse, crack during tightening.

And perhaps I'm just dwelling on unimportant details. I tend to overthink some of these things, sometimes. :lol:

Thanks again for all the help.
Hal
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[Anonymous]

I don't think that's too much tape. Basically you are just filling in the gaps. In high pressure applications you can wrap it 8 or 10 times. I usually go 4 times for instances like this.

 

[Anonymous]

All of those wraps in the pics are in the same direction as the threads, which is what I thought was the correct way to wrap. Some people say to wrap it in the opposite direction of the threads.

Louey

 

[hfmann]

Matt, just so I'm clear on this. You cover the entire length of the threads with usually 4 layers layers of tape, somtimes 8 or 10. right?

Louey - all the folks I've talked to say the tape should be wrapped clockwise in the direction of the threads. That way as you tighten the fitting, you are tightening in the direction the tape was wound. I used to get pretty confused, but now it makes sense to me.

And....this afternoon - I'm very glad I threaded that first section. The way I had a union and elbow on the inlet pipe would make me raise my hood and lights 3". So I took the fittings apart and reversed the position of the elbow and union. Now I only need another 1 1/4". Glad it was threaded!

So now....what's everyone's favorite way of removing the old tape before putting the new on? Getting all that tape out of the threads was fairly tedious. As tempted as I was to use some sort of wire brush, I thought that might damage the threads. I ended up using a tweezers.
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[Anonymous]

Well the reason you use 3 "layers" is because the tape helps prevent leaking under pressure situations since if you over tighten it you very easily can rip the tape and make a potential leak point.

With PVC I wouldn't cover the ENTIRE length of the threads since the PVC fitting you're working is probably is tapered and as a result you can't screw them all the way in, I would dry fit it first and mark with a sharpie or something to mark how far in it'll go and use tape to that point.

 

[Anonymous]

Yes, for some plumbing and DIY components (calcium reactor, bubble counter, etc.) that I built, I often test it with air with a bicycle pump along with a pressure gauage. For smaller parts, I just submerge it into a water reservior I have in the yard for RO waste water.

>Some people say to wrap it in the opposite direction of the threads.

Louey, I never understand why anyone want to wrap it against the thread. Did any of them give you any rationale? Maybe it was just a mistake in description :?

I have not find any good way to remove the telfon tape. Usually, if it is difficult to get every piece out, I just wrap a new layer over the old. :?

 

[Shipbuilder]

I have been gluing pvc threaded fittings together for years.
Don't ever remember glue setting before tighting all the way.
No problems yet.

 

[minibowmatt]

I have seen people use a little silicone on their threaded fittings. Just put a dab on the threads before you thread them together. The silicone will seal the gaps, and should prove removable in an emergency. However, you will need to add cure time to your project.

 

[Anonymous]

I would not glue them. I only use threaded when necessary. A couple of wraps of teflon tape and good to go.