Connecting PVC Pipe to Steel Valve?

[Elle]

I am re-plumbing part of my pool filter system. Previously, a 3/4-inch metal valve was threaded to 3/4-inch PVC piping. The PVC piping had a PVC male adapter, which fit into the female threads of the metal valve. I am replacing the male adapter but find it is a very tight fit. A lot of torque would be necessary to get it into the previous depth.

I have a 1.25 inch metal valve connecting to a 1.25-inch PVC male adapter with the same situation.

Do I just use teflon tape on the threads and then apply a lot of torque until each PVC male adapter inserts at least halfway into its metal valve?

[Tom J]

I find that PVC pipe, mostly from China now, varies in dia slightly, so just screw it in until you feel it's tight. Water test for leaks & tighten more as needed. Over tighten stresses the plastic!!

Tom J

[Duff]

Exactly.

Instead of 1/2 way, just make sure you have a few threads in and you should be fine. Use any compound you wish or no compound.

Spend a little time at your supplier screwing in valves to the PVC joints and find a pair that fits.

[Elle]

Thank you very much for sharing your experience Tom j and Duff. It's raining here today, so I am not doing more than a little measuring, cutting, and gluing. I will try the teflon piping dope.

Unfortunately the valves have to stay in place, and it's a bad idea to replace them due to the piping starting underground within about six inches of the valves yada. So I can't try adapters and valves at the supply store to get a good fit in advance.

I will report back after the job. It's a little tricky because I have to glue other joints before I can apply the operating pressure to the two adapter-valve joints under discussion. And as you all know, once glued... I may put in unions to help ease the pain of a mess-up at the valve(s), due to yours truly not being experienced enough in plumbing.

[Elle]

Hi, just an update for the archives. I was not having any luck with good thread contact area with the old brass gate valves. This was even after "chasing" the threads with a steel fitting (no tap handy). Consequently I replaced the brass valves with new PVC ball valves, threaded. I noted in advance how much farther the new PVC threaded fittings advanced into the new PVC valves, Duff. Huge difference. I used teflon tape. The joints are much more mated, due to the male adapters' threads inserting farther. All is holding well, plus the system is quieter when the pump is running. I have some apprehensions about the PVC valves longevity, but good enough for now, plus they are way less expensive than new brass valves. Thanks again for sharing your experiences. Elle

[Tom J]

Just to add a caution. Over tightening PVC threaded joints may cause the female part to split from the excess pressure. I had it happen a couple of times before I decided they didn't want to be as tight!!

Tom J

[Elle]

"Tom J" wrote

I have indeed been trying to get away from the "more tight is better" mentality with PVC. Thanks, this helps.

[z]

I have a theory, that how tight I make the connection relates to how tight I was when i made it. I have another theory regarding joints which i will not go into here.