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wallix 08-05-2009 09:49 AM

Leak Under Kitchen Sink
Recently I was under my kitchen sink and discovered a pool of water under it. Upon further investigation I noticed a moderate drip on the cold-water valve. What was odd (to me, at least) was that turning the valve on or off had no effect on the drip rate. I then discovered that the drip was actually on the line-side of the valve (As seen in the second picture). It looks like it drips where the line connects and then dribbles off the bottom.

I have never done any plumbing beyond changing a shower head. Is this something I can fix with my limited skills, or should I call a plumber? I have never shut off water to my house before and am afraid I will mess something up horribly. If I can fix it, what do I do exactly?


kok328 08-05-2009 12:08 PM

I can see your hestation. The first rule of plumbing that I realized is that once you mess with this type (PVC to brass) of connection, your opening a can of worms. Luckily, you have plenty of PVC to work with in the event of not getting it right the first time. However, you may be able to shut your water off at the main, undo this connection and put some plumbers string around the compression fitting and retighten it to stop the leak. I'm assuming this had been a problem for awhile now based on the presence of corrosion. If your still hesitant to go there, a well placed bowl should keep you from rotting out the bottom of the cabinet.

Nestor_Kelebay 08-05-2009 02:17 PM


Let me preface by saying I've never worked with PVC pipe before, but if Kok's gameplan doesn't work, then I think it would be best to get rid of that Brasscraft stop altogether. Whomever did this work gooped pipe dope on the compression nuts, and that tells me they didn't understand that the threads on those nuts don't form the seal, and that in turn means they really didn't know what they were doing. (See note below.)

If you have trouble fixing that leak, I'd suggest you take the Brasscraft stop off entirely, clean up the pipe end or cut off whatever can't be cleaned up and cement on a male pipe thread adapter:

Then, onto the pipe thread adapter, screw on a PVC ball valve:

That way, you can always shut that PVC ball valve to do any repairs downstream of it, and if push comes to shove, you can always shut off the water to the house to replace the PVC ball valve.

I'm thinking that this is probably within a "newbie's" ability since the only "new" thing you might be doing is cementing the MIP adapter onto the PVC pipe.

And, you should be aware that if you buy a good quality pipe cutter for copper pipe, (from a company like Rigid, say) you can order a cutter wheel for plastic pipe from any plumbing wholesaler (who'll prolly sell to you as long as you pay in cash at the time you order). I'm thinking that if you just order a cutter wheel for plastic pipe for a small Rigid pipe cutter, there's a pretty good chance it'll fit any el-cheapo pipe cutter you can get in a home center or hardware store, and if you can't find a pipe cutter it'll fit, you can then always buy a Rigid pipe cutter. Rigid is a well respected name in plumbing, and they make quality tools.

All you need is a bit of practice priming and cementing PVC pipe fittings onto PVC pipe.

I'm not sure of the best way to get from the PVC ball valve to the supply pipes for the faucet, tho. Hopefully someone else with lotsa experience with PVC piping will chime in on that.

Note below: The reason why it's wrong to put pipe dope on compression fittings is that thread sealants like pipe dope and teflon tape rely on the fact that the "NPT" or "National Pipe Thread" threads you find on plumbing fittings are tapered, like the threaded ends on drill pipe:

Because of this taper on both the male and female threads, the threaded joint becomes tighter and tighter (and therefore less prone to leak) as you screw threaded plumbing joints together.

The purpose of pipe dope or teflon tape... (like you see below):

(it's best to wrap the tape in the same direction the female thread screws on so as to "stretch" the tape as you screw the female fitting on) to plug any residual gap between the male and female threads to form a leak-proof seal.

The threads on the compression fittings on your Brasscraft valve aren't tapered. They're straight just like the threads on a light bulb or a bolt. That means that there's never any compression of the pipe dope or teflon tape between the male and female threads as the joint is screwed together, and that means that using pipe dope or teflon tape on straight threads doesn't help prevent leaks.

So, you WOULD use teflon tape on all your male plumbing threads when assembling your piping. But, you would NOT use it on any "non-NPT threads", like the threads on compression nuts or hose ends, for example.

Another way to look at this is to ask yourself: Where does the water tight seal actually occur? In the case of a compression fitting (like you have two of on your existing valve), it occurs around the ferrules under the compression nuts. The threads on those nuts simply exert pressure to deform the ferrule sufficiently so that the ferrule seals tightly around the pipe and against the fitting, the threads themselves don't actually form the seal. So, you wouldn't use teflon or pipe dope on them. Similarily, if you look at a garden hose, it's the washer in the female end of the hose that forms the seal, not the male and female threads. But if you look at the way iron piping is assembled, there is nothing else except the threads to form a water tight seal. So, those threads must be tapered SO that something can get squished in between them to form a water tight seal. That something is typically teflon tape or pipe dope, sometimes both (which I don't see any sense in doing).

kok328 08-05-2009 06:05 PM

Eventually, you'll have to convert from brass or copper to PVC. That's what I meant by opening a can of worms. You end up replacing just about everything under the sink just to stop one dripping connection. A slight deviation to Nestor's approach would be to remove the shutoff valve, prime & glue on the male threaded pvc nipple and wrap those threads with teflon tape and then reinstall the brass shutoff valve.

Nestor_Kelebay 08-05-2009 09:33 PM


Originally Posted by kok328 (Post 32985)
A slight deviation to Nestor's approach would be to remove the shutoff valve, prime & glue on the male threaded pvc nipple and wrap those threads with teflon tape and then reinstall the brass shutoff valve.

Kok didn't mean to say that you could put that same valve back in. He meant to say that you could screw a similar kind of valve onto the male pipe thread adapter; one meant to screw onto the end of a pipe and provide a 3/8 inch compression outlet just like your existing valve does.

You can't use your existing valve because it's the wrong style. It's not meant to screw onto a pipe thread. It uses a compression fitting to seal around the perimeter of a copper (and presumably PVC) pipe. You'll need to buy a new valve that screws on to a 1/2 inch NPT pipe thread.

wallix 08-06-2009 01:39 PM

Thanks for all the suggestions. Would the easier and cheapest way be just to get another brass compression valve like the one that's one there (assuming it will probably fail, too, as the years go by) and replace it?

Nestor_Kelebay 08-06-2009 04:07 PM

No. What you have there is a valve intended to be put on COPPER pipe. Someone has stuck it on plastic pipe, and that's prolly a big hunk of the reason why it's leaking. I think it would be best to use fittings appropriate for the kind of piping you have.

That kind of plastic pipe you have in your house might not be PVC. I just happened to be in my local plumbing wholesalers today and the guy next to me had the same white plastic pipe like you have, and he said it was "PEX piping". This is a new kind of piping system that a lot of houses are being built with.

I've never worked with PEX piping either, but my understanding is that the fittings for PEX plastic piping come in several different formats.

From what I can see, the most common type of PEX format looks like this:

The above is a PEX ball valve.

You push the fitting INTO your plastic tubing and then use a crimping tool to crimp a ferrule onto the OD of the tubing. This is what the crimping tool looks like:

A tool like this costs about $100 or more, but you can rent them at home centers like Home Depot.

Here's what the complete installation looks like, only with different kinds of valves:

So, can you go in your basement and see if you see those kinds of connections on the exposed piping? If your exposed piping has connections like you see in this picture instead:

(Note the cemented PVC fittings in bottom right corner of picture.) Then it's PVC (actually chlorinated-PVC, or CPVC) piping. CPVC stands up to higher temperatures better than PVC.

If you have CPVC pipe, then you can get PVC valves to replace that leaking brass valve you have now. Here's a picture of such a PVC valve:

I found it here:

Nestor_Kelebay 08-06-2009 06:10 PM

The valve shown in the above picture is made by Genova Products. It's sold online by Aubuchon Hardware:

Find Water Supply Line Valves and other Valves at Aubuchon Hardware

Or, contact Genova at:

and find out who their distributor is in your area. Then contact the distributor and find out who retails Genova products in your area. That store will either stock that valve or will be able to order it for you.

If you have CPVC plumbing, THAT'S what I would replace what you have with.

Redwood 08-06-2009 07:48 PM

Whoa There! Let's not get all Crazy!
Whoa there lets not get all crazy about this...:eek:
That pipe is CPVC and not PVC! There is a difference!

There are 3 options 2 of which I would consider to be good ones and the third while it would work I would consider it to be less attractive.

Option 1: Would be to replace the valve with another compression valve. I would recommend using a 1/4 turn angle stop valve like a Brasscraft # KTCR19 C or, G2CR19 C

Option 2: Would be to replace the valve with a valve that is designed to solvent weld to CPVC using CPVC Cement. Again I would recommend a 1/4 turn angle stop valve but this time the valve would be a Brasscraft # KTPR19 C or, G2PR19 C

Option 3: While it would work is one that I do not care as much for but it will work. It involves the use of a valve that simply pushes on and locks in place on the pipe. The thing I don't care for is these valves will rotate on the pipe even when properly secured. The valve would be a Brasscraft # G2PC19 C

Link to Brasscraft Catalog PDF

Whatever path you choose the CPVC will have to be trimmed back past where the compression fitting marked the cpvc pipe to get a proper seal. The whole house will have to have the water shut off while doing this work. No Teflon tape should be used on this repair job!

I would also plan on replacing the supply line up to the faucet with new braided stainless steel supply line.

Nestor_Kelebay 08-06-2009 09:34 PM

But Redwood, wouldn't all of those options involve having to cut the pipe again should he ever need to replace that valve again? As the owner of the house, one of the thing's Wallix is going to be concerned about is that eventuality.

If you're suggesting he put in a brass valve, then wouldn't it be ultimately better to cut the existing valve off, cement on a PVC male pipe thread adapter and screw on a standard Brasscraft stop intended for threaded pipe? That way replacing that valve in future doesn't involve cutting the pipe any shorter.

Also, I know that a quarter turn ball valve is "slicker" than the regular compression style, but the advantage of the regular compression style is that if there's ever any problem with the valve, it could usually be solved simply by taking the old cartridge out and putting the cartridge from a new valve in. Wallix says he/she's got very little plumbing experience, so that might be a feature that would be attractive to him/her.

I'm not sure if the PVC valve I was suggesting would crimp anything onto the pipe or not. Specifically, anything that would require cutting the pipe if the same kind of PVC valve were no longer available in future.

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