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 has a PVC male adapter, which fits into the female threads of the metal valve. I am replacing the PVC 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?

Thank you in advance.

(Posted also to alt.home.lawn.garden.)

[Oren]

I use Teflon tape in this situation.

[Richard J Kinch]

Tape, yes. Excessive torque, no.

[Oren]

A fine line between torqued and a cracked PVC. :-)

[Mamba]

An alternative to teflon tape is also non-hardening thread sealant. It helps act as a lube for pipe tightening. I used it to connect my 1.5" PVC from my household pressure tank to metal valves controlling my in-house supply. I got an extra couple of turns out of it using the sealant, which cured a slow leak problem I had after my initial installation.

[Joe]

Another well regarded sealant is Teflon pipe dope. Very slick and non hardening. HTH

Joe

[jim]

Pipe dope is the best yes

[franz frippl]

I'd be careful putting too much torque on anything PVC. Too much and you could split something and then have to start all over.

I have been using teflon piping dope which does a nice job of sealing and lubricates threads so things go together easier.

[Elle]

Thank you very much for sharing your experience Oren, Richard, Mamba, Joe, Jim and Franz. 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.

I have been learning the hard way that the key to a good thread fit (with PVC) is not overtightening, so the re-emphasis on this by several of you helps.

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.

[Oren]

I have a brass Resistant Pressure Vacuum Breaker similar to this photo. Connecting the whole works was fun. I don't use the 1/4" fittings ( could make misters for Summer) . With a brass T I have a hose bib (ball valve) and the pool filler/water supply connected. PVC to the pool from 3/4" too 1/2" on an elbow reduced.

I might change away from tape in my case. I live in the desert and sealant might be better than tape.

[Elle]

Hi, an update:

I tried the teflon thread sealant with the old brass valves and the new PVC fittings. I also tried the tape and "cleaning" the valves' threads with a steel pipe fitting. A real tap, from a tap and die set, is not convenient. No luck; the joints leaked. Plus, I suspected the PVC-valve joints I was hoping to leave alone, some eight years old, would soon start leaking. So I replaced the valves.

I bought PVC ball valves, 3/4-inch and 1.25 inch to replace the old brass, gate valves. I actually throttle one of the valves to adjust the flow at times, so ball valves are better for this. Generally though the valves' positions are fixed for months at a time. Large diameter PVC ball valves are often difficult to operate and so test the strength of connecting joints, so I remain apprehensive about how well this will work in a few years. Just recording these thoughts for the archives.

Since the PVC pipe proceeds into the ground just a few inches beneath each valve, I wanted to cut and cement as little as possible off these ends. What "saved" me is a PVC fitting called a "male compression adapter." It has male threads on one end and a compression fitting at the other. The 1.25 inch size adapter (mostly or entirely made by Mueller B&K) was hard to come by, but I finally found a couple of Ace Hardware stores that have them. Lowes and Home Depot do not. I used teflon tape on the male threads.

All seems to be holding well; no leaks now. Plus the system is quieter when the pump is on. Not sure why exactly that is, but surely the joints were weak, or the metal of the old valves loaned itself to facilitating air knock leakage cavitation yada.

Lessons learned from reading and working with old and new PVC fittings and brass valves: Partial replacement of old PVC piping systems can grow into bigger jobs. Replace as much as possible. I am sure cement joints are more reliable and cheaper, but I wanted "forgiving" parts in this, one of my first experiences re-piping with PVC. Also, I was trying to avoid having to dig up PVC piping (about ten feet in distance, maybe four feet deep, from pool filter system to pool).

I am sure the experienced folks could have nailed this in a few hours. I'm in it for the experience. :-)

Oren, noted that sealant may be better than tape in the desert. I am in desert, too.

Thanks again all for sharing your insights.

[Oren]

Oh, Yeah! What exit? (NJ joke)