Fixing Threaded PVC Pipe Leaks?

Factual Questions
1

Great Googly Moogly!

There’s a leak in my brand-new lawn sprinkler system where the sprinkler valve (or valves) are screwed to PVC pipe. As a result, the underground valve box is full of water. The whole assemblage of pipe, elbows and tees is cemented together, there’s no opportunity to turn the threaded connections at all.

To repair this by “proper” means would involve digging up and cutting all of the pipes connected to this collection of valves as everything but the valves themselves is permanently cemented together into a 3-D puzzle. Rather than having to chop apart and rebuild it all, is there any hope for being able to shut off the water, let everything drain out and dry off, then paint the threaded connections to the valves with purple primer and PVC cement? Will the primer/cement have any chance of wicking up into the threads to seal them?

2

Teflon tape?

3

It’s not possible to unscrew and re-assemble or even attempt to tighten the threaded joints.

4

As one who owns a house with a sprinkler system, and having replaced virtually every valve and sprinkler head at least once over the years, I regret to inform you that you are screwed. If you try to seal the threads with PVC glue, it may work for a little while (read: a few minutes) but this is not a permanent solution.

One thing that I have found to be invaluable is a repair coupling which telescopes to whatever length you need. I try to put these in wherever I connect to a screw fitting, such as a valve.

Glue the solid end to pipe which feeds your sprinklers, and glue a screw thread fitting to the telescoping end, which not only telescopes, but rotates as needed. Then you can tighten the threads as needed without disturbing the rest of the system.

PS. Definitely use teflon tape when you redo your threads.

5

In my experience, doubt whether cementing the outside would do any good, but might be worth a try first.

I can’t quite figure out from what you wrote whether you are talking about one of the actual sprinkler heads, or the inground box where the main valve-solonoid with wires from the timer are. If it’s the latter, then it absolutely shoud have been put in so it could be unscrwed. Is it leaking from one of the threaded joints or one of the cemented ones?

As you say it’s brand new, I’d contact whoever installed it and have them fix it.

There should be a gizmo installed there with counter threaded hex nuts so it could be unscrewed and everything taken out. That’s what my many-years-old system has.

If there is enough space, you still may be able to cut through a straight piece of pipe, install this gizmo, and then next time it will be easy to get out.

If the installer can’t be contacted or be made to fix it, go to an irrigation shop, describe the problems (or show them a picture of it) and see what they suggest. Usually they can supply you with whatever parts you need, and then you can fix it. If there are none in your area, you can try Home Depot.

Of course, for any screwed joints, you definitely should use teflon tape.

Good luck!

6

If it’s threaded pipe, it shouldn’t be cemented (glued). They should have used teflon tape. If it is threaded pipe you can buy a fitting called a “union”, then cut the pipe a few inches from the leak and replace the leaking fitting/pipe and reassemble using the union in the line. Go to a hardware or home supply center and ask them to show you how. If the pipes are cemented you should be able to buy adapters to replace the leaking parts w/ glue joint pipe.
Again, any good hardware or home supply center should be able to show you how to make the repair. You’ll need to know the pipe size and whether it glue joint or threaded.

7

I used to do this for a living and can probably help you.

It sounds like you’re describing the manifold, where all the lines from the various zones come together in a valve box with the electric valves and tie into a live line. (I’m guessing here, because I can’t see it IRL.)

First off, while it’s probably disconcerting to see the manifold for a new sprinkler system completely under water, this won’t likely harm your electric valves.

Check the valves themselves. One might have an open or busted bleed screw. You should see plastic screws somewhere in the vicinity of the electric solenoids. Make sure they’re tight and not leaking.

Now, for the bigger problem. Manifolds are a pain in the ass to repair, because of the difficulty you described. If a manifold tee springs a leak, often the valve box has to be dug up, the individual lines have to be cut after the electric valves, and most of the manifold will have to be disconnected from the live line.

Let me say that there’s no reason why your irrigation installer should have glued the manifold tees together. Most of the manifold tees I’ve seen thread together and teflon tape or paste keeps the threads tight. Now your whole manifold likely has to come out of the ground.

Shut off the water. Dig up the valve box. Then, dig back each individual line at least two feet and cut the poly pipe after the electric valve. Disconnect the live line leading into the manifold (you may have to cut this if the fitting is glued or you otherwise can’t turn the manifold). Once you have the manifold out of the ground, get rid of the crappy glued manifold tees and rebuild the manifold using threaded tees and some teflon tape or paste. Couple everything back together, using the appropriate couplings. (You didn’t say whether the line leading to the manifold was PVC, copper or what have you…) Couple the individual lines with insert couplings and squeeze clamps.

Sorry that this is probably the only solution that can help you. It’s probably a couple hours of labor, depending on how many zones you have and how much room you have to work. On the positive side, it shouldn’t cost you more than $20 in materials. Trust me - I’ve tried every kind of stop-leak there is to repair manifold leaks. Repairs rarely last more than a couple days. If it were me, I’d rebuild this thing, ensuring it will give you years of reliable service.

8

I used to do this for a living too. It sound like the leak is at the threaded nipple between the valve and the manifold. As THespose said you may need to dig up the box and dig a few feet of ‘zone’ line out of the ground. Again, it depends on the type of line it is. Most likely its that black sort of flexable stuff commonly refered to ‘poly’. Then unconect the line that goes out to a ‘zone’ remove offending valve, apply new teflon tape and screw valve back on. I see no reason to replace the whole manifold unless you have additional leaks. And IMHO a glued together manifold is infinitly beter than a screw together one.

9

Also, before you dig it up, check where the control wire is. It usually follows the main line that feeds the manifold. But you never know. In any case, it is low voltage and won’t be charged if your sprinkler isn’t running any zones.

10

The black pipe is polyethylene. You can cut it back and try to rotate the whole piece such that the valve threads onto either the nipple or the end of the manifold tee better. (Most setups I’ve seen don’t have threaded nipples feeding an electric valve. They usually thread right to the manifold tee.)

IMHO, a glued-together manifold is a remarkably bad idea. Threaded manifolds offer additional flexibility in repairs, hold together just as well as glued manifolds, and involve fewer parts. Fewer parts = fewer things to go wrong.

11

**THespos ** and **enipla ** are on the right track. It is where the valves are screwed into the manifold. (And here I was afraid to use that term, thinking nobody here would know what it is)

Yes, it was surprising to see the valves submerged under water. I’m not terribly worried about the electrics, unless the grease caps eventually leak. I’m more concerned for the anti-backflow / vacuum break side of the valve. If that part’s under water, would that potentially allow water to backflow into the house potable system?

The manifold is a home-built assemblage of elbows, tees and slip-to-NPT thread adapters. All eternally cemented together. Pipe in and out of the valve box is shedule 40 PVC.

Oddly, I did have one valve with a stripped bleed screw, and I had to do a head-swap on it, as it was the threads in the valve body that were stripped. This failure was pretty obvious as it started squirting when the supply valve was opened and that zone spontaneously started spraying.

Unfortunately, the installer is “us” - myself and a couple friends. On the plus side, the sprinklers themselve work great.

Guess I’ll just have to dig the thing up and rebuild it this weekend. :sad:

12

As for threaded vs glued manifolds, the options available to me were to buy a threaded manifold that appeared to be specifically built for a brand of valve the store didn’t sell, and that they didn’t have all of the requisite parts for (WTF?) or to cobble one up from bits of PVC.

13

Threaded PVC should be outlawed. In fact it is (by building code) in many places.

If you MUST use it, use it with rectorseal teflon laced pipe dope. Teflon tape is more lubricant than sealer. This encourages the pipe to be overtightened, extruding all (or at least most) of the teflon out of the joint. First change of temperature, and it leaks a little, so you tighten it. Next change of temperture the female half splits and leaks NOT a little.

The pipe dope is sticky, discouraging overtightening. It has some give, which discourages leaks.

Best bet is glued (solvent welded) PVC or sweated copper.

14

Oh, and forget putting glue on the surface to stop leaks. On rare occasions that works in the short term (days, not weeks). In a proper glue joint, the solvent softens the plastic, and the plastic actually welds. The joints are made to be interferance fit, so plastic is actually displaced when you shove the pipe into the socket. This provides mechanical cross linking of the polymers. None of that happens when you just smear glue on the surface.

15

Is there a reason (other than appearance) that these manifolds are typically buried underground?

Seems like it would be much easier to work with if this box & all the stuff in it were attached to the side of the garage, a couple of feet off the ground. The bit of extra pip needed wouldn’t cost much. And presumably it’s only used in warm weather, and freezing isn’t a concern.

Is it just a matter of wanting this all hidden from view?

16

Not sure what code is in San Francisco, but backflow prevention devices are code here on Long Island. We’ve got double-check valves here. Do you have one on the line that feeds the manifold?

I really haven’t done too many systems off Long Island, so I’m not sure what other backflow prevention devices are out there. If you do have a double-check valve, though, I wouldn’t worry.

17

Note sure what to say here. Sounds like you have backflow prevention on each valve? The way we did it (code at the time) was to put a double backflow system on the main incoming line. I seem to remember that valves with backflow preventers are sold, but not sure. Whats the make/model of the valve?

Good call on THespos part.

Also, the good news is that since you put it in gotpasswords you’ll be in a better position to work on it. I worked for three companies (one I owned) as designer, installer and maintenece/repair. For the most part, I always found it was easier to bite the bullet and pull the valve box for the repair you are trying to do. It’s a real drag to dick around with it for an hour, only to realize it would have just been easier to dig up the box and do it.

Partly, I suppose. And I’m sure it’s against code. There are also other reasons. Many systems have at least two valve boxes. A properly installed underground box should last years and years (with the occasional fail). Usually, the parts that fail are the solinoid or valve diaframm. All easily replacable from a box.

We will have to agree to disagree. I used the threaded, (Greenlawn?) tee’s and had nothing but problems with them. A properly built manifold made of glued PVC becomes one part. You still need to screw the valves into the tees (limiting the point of failure), but a poorly glued PVC joint will fail when you charge it; or never.