Glue PVC threaded fitting; unwise?

[Anonymous]

What's the point of getting more expensive threaded fittings if you're going to glue them? :?

The advantage of threaded is you can remove and change the fittings.

hfmann,
I have only done 8-10 times on RO/DI systems where there's more pressure. 4-5 times is suitable for me on everything else.

 

[Shipbuilder]

The only threaded fitting I use are hose barb fittings. Remove hose to take things apart.
Most of the hose barbs I have purchased at Lowe's are molded and the mold seam goes right thru the threads. Have had leaks in the past where teflon tape did not seal at these seams. I even tried trimming off the seam with a knife. This works but only on the ones where there is not a mismatch on the mold. When there is a mismatch the gap is usually too big for the tape to seal . Thats when I reach for the glue! Actually trimming inbetween the threads is a p.i.t.a. so I just glue em all now.

 

[Anonymous]

Yeah, threaded PVC part is done with molding method. This applies for both female and male parts, and if the batch is done on a Friday afternoon, the thread can be off like you described.

For certain applications, people often drill & tap or mill and use die to make the thread. It is possible to use a die or tap to reshape the PVC part for better fit instead of go at the seam with a knife.

 

[hfmann]

Hey guys - thanks for all the help. You can always count on this board to jump in with a lot of help.

At this point you've all convinced me that I should be able to make leak free threaded joints without too much fuss.

Shipbuilder – Thanks for letting me know that’ve glued these fittings and it works well. Now I know it wasn’t a stupid question! And I never gave it a thought about those seams in the barb fittings. I’m certainly going to keep that in mind the next time I use a hose barb fitting.

Minibow – Interesting! Silicone? The caulk kind, or the lubricant? And instead of tape or in addition to it?

Seven – What kind of pressure gauge screwed into the system to see if the pressure holds? ? I thought leaving the old tape in place create little bulges the hinder the seal? Surprising! Are the threads on PVC just standard pipe thread? If so, I can see people using a die or tap to rethread the fittings.

And SF, thanks for the tip on marking the threads. No need to waste the tape and less to removed later on when dismantling /and reusing the parts.

Matt – the ONLY reason I was going to glue the threaded fittings was because I already had them and couldn’t return them. Agree it makes more sense to buy slip fittings for the glued sections. And thanks for the experience on the number of “wraps”.

Hopefully this coming weekend, I'll have this whole thing up and running.

Thanks again.
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[Anonymous]

>..What kind of pressure gauge screwed into the system to see if the pressure holds?

It is just a regular air pressure gauge with a 1/8 or 1/4 inch NPT. I think you can use the water pressure gauge that people use for the RO/DI. Should work with water or dry. Here is a pic from MarineDepot:

All you need is a PVC brushing with 1/4 or 1/8 inch thread that you screw the gauge onto. I use a 1/8 vinyl tubing with threaded barb adaptor as input. Basically pump air with a syringe or bicycle pump thru the vinyl tubing, clamp it close, and remove the pump. Read the pressure and come back later to check the reading. You can do it without the gauge, just dunk the entire plumbing module into water and watch for air bubble. Obviously, I have spare union parts that I use to close off all the openings. Can be a pain, but it is worth the tme if you want to make sure there is no salt creep a few week later.

I usually remove as much of the telfon as possible. But they are soft enough that they will flatten out once you tighen the connection, and does not hurt the seal.

Yes, the threads on PVC part should be standard National Pipe Thread (NPT), which is tapered. There are taps and dies for the NPT, but they can be expensive. I think www.harborfreight.com sell them, but if you only need one or two, it can be something that is not worthwhile to buy. The largest tap i have is 1 1/2 inch, and I only use it 3 times in 6 years

 

[hfmann]

Seven,

Great info on the pressurizing technique. Thanks. Looks like a great way to verify / fix the leaks ahead of time.

I usually remove as much of the telfon as possible. But they are soft enough that they will flatten out once you tighen the connection, and does not hurt the seal.

Glad to have your experience on this. Sounds like I don't need to be so concerned about it.

Great! I can borrow the NPT taps and dies from work if I need them.

Thanks for all the help.

Hal
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[minibowmatt]

Yup-- just regular clear silicon, the caulk type. It will flow very easily in the threads, but I guess if you put too much in the thread, it will push out and into the interior of the fitting.
I have never used this method, but I may when i build my new tank.

 

[trido]

hmm... when I plumb people showers and sprinkler systems Ido not implement any of these techniques.....UH OH!!! Definately dont glue them.... pipe fitting are cheap IMHO

 

[hfmann]

Seven,

In pressure testing - How much pressure do you pump the system up to? Since I don't have a bicycle plump, I was thinking of just jacking my air compressor down to the right pressure and using that. Do you think would be safe enough?

Update - I'm dry fitting all my parts together today. It's been a learning experience (so far ) and many, many trips to the plumbing supply section. In fact on my back there now, as I ran out of teflon tape.

Hal
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[Anonymous]

Bike pump is recommanded. I am sure some of your neighbors has one in the garage. Depends on the volume of your plumbing, your compressor can overshoot the pressure so quickly that it can damage the part.

Depends on the part you test. For regular plumbing, I only do1 5 psi or 20psi. For an acrylic bubble counter that I made, I put more than 50 psi, and it holds up very well. There is no hard rule, just keep in mind that PVC plumbing part is rated for at least 120 PSI (I think :?), and the higher the pressure, the faster you can see the pressure drop or bubbles come out under if there is a leak.

Oh, wear eye protection if you go anything more than 20 psi.

 

[hfmann]

Thanks Seven,

I admit I was afraid of the compressor overwhelming the system and blowing something up. And then all that work - kabloom!

Thanks for the info.

Hal
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