PVC valve + 1/2" FIP sink hose = leaks?

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Akagis_white_comet

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Hello All,

I'm Travis and this is my first post here. Coming from the world of Rotary Engines (3-rotor RX-7 owner here... ;)), I'm pretty well-versed in electrical, mechanical and plumbing when it comes to oil/coolant/fuel/etc. Since our cars use NPT connections here and there, I know how to teflon tape metal pipe connections correctly. But what is troubling are the nonmetallic NPT connections.

My fiancee and I bought a mobile home built in the early 70s on the cheap. No surprise, the plumbing was in abysmal condition due to prior owners' "repairs", a combination of copper, galvanized, brass and anything else found at the big box stores' clearance aisle. between this and a scary number of fittings applied to every junction, the writing was on the wall.

After having three different lines fail in two weeks, plus the hot water heater (from 2006) due to incorrect practices, I determined that ALL of the supply plumbing was suspect and we decided to start completely fresh on it. The plan was to run fresh CPVC pipe inside the house, eliminating all of the old stuff from the house as a whole.

I know how to correctly handle CPVC and opted to go this route to keep the project cost as manageable as reasonably possible. I extracted the old Umbilical line, disassembled it and found that it was cobbled together and in rather poor condition. Removed the copper from it, then cleaned it up and reassembled it. Re-routed it to the Kitchen in place of the bathroom to eliminate as much plumbing exposed to cold as possible. Put a Main Shutoff Valve (sillcock with flange mount, Lowes# 21508) inside where it enters the house. This works fine and has no issues.

With all of the external plumbing resolved, I started on the inside. As our hot water tank was on its last legs, we opted to go with two smaller tankless water heaters. One for Kitchen and one for Bathroom, in order to cut the plumbing effort in half. Did the whole kitchen in CPVC, adding a branch line for the refrigerator (planning for a newer one with ice maker later) and dishwasher. The way I did this was with a 1/2" CPVC Male Adapter at each device's connection, and a 1/2" PVC quarter turn Ball Valve to shut off the supply for servicing. These were cheaper than regular shutoff valves and far easier to mount solidly on 1x4s

Did a test on it, no leaks where the valves meet the CPVC male adapters. So I continued onward to the bathroom, using the same logic as the kitchen. All is good so far. The only exception to this are the washer's lines. CPVC male adapter meets 1/2" braided stainless steel sink hose (IPS/NPS thread, with the gaskets in both ends). Then a 1/2" brass hex nipple, 1/2" PVC street elbow and finally a flange mount sillcock (Lowes# 21508 again).

All of the aforementioned washer plumbing is housed inside a removable panel, with the sillcocks protruding through.

So here's the problem:
#1: Female Brass threads (Sillcock) + PVC Male Thread (on street elbow)
#2: PVC female thread (street elbow) + brass male thread (nipple)
#3: Brass Male thread (nipple) + Female Stainless thread (sink hose)
#4: Female Stainless thread (sink hose) + CPVC male adapter (supply line)

#2 leaks despite having 2 turns of regular white Teflon tape and being tightened to the point that 3-4 threads are still visible.

There are similar connections I've had to make which also leak. For example, the Kitchen sink's cold supply line has a 1/2" PVC valve, brass nipple and then the braided stainless hose running up to the faucet. It leaks where the nipple meets the valve.

Did I do something wrong or miss an important step?
 

Terry

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You can't use plastic female threads. They often split. I know they sell them, but plumbers don't use them.

cpvc-male-adapter-terrylove.jpg
 
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Akagis_white_comet

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You can't use plastic female threads. They often split. I know they sell them, but plumbers don't use them.

Before putting the brass nipple(s) in place, I attempted to use Polyethylene Riser nipples (https://www.lowes.com/pd/Orbit-6-in-Cut-Off-Riser/1063721) as a test subject. They are NPT on both ends and have a wrench hex, but the sink hoses did not want to thread on consistently straight. As far as material selection in this case, I know it was incorrect due to it being labeled for outdoor cold water use only.

With the polyethylene nipples, it leaked at connections #2 & #3. At the same time, I went rather light on torquing them for fear of shearing the threads off, so this may contribute to the leaks. Strangely, #4 is dry as a bone so it is only adding to my confusion in this case. Could you please shed some light on this?
 

Reach4

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With cheap white PTFE tape, think 6 to 8 turns plus CPVC-safe pipe compound, such as Rectorseal T plus 2. Three turns of the better PTFE tape is OK.

I think cutting the tape is better than tearing, but others may differ.

There is more than one good leakproof way. I like yellow or Oatey pink with 3 turns. I like the pipe compound too. I am not a pro, so I want margin to make up for any shortcomings.
 

Akagis_white_comet

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You can't use plastic female threads. They often split. I know they sell them, but plumbers don't use them.

Since the valves are PVC female thread, I consulted with a friend and came to the same conclusion that you did. Female threads need to match the male threads' material or be harder. Ideally, they should be the same material to prevent shearing. So...

PVC female fitting + PVC male fitting = Good
Brass female fitting + PVC male fitting = OK, not ideal (male threads can be sheared if overtorqued)
Brass female fitting + Brass male fitting = Good
PVC female fitting + Brass male fitting = Bad

So I hit the store, got some transition male adapters and made some transition nipples. 1/2" NPT male CPVC on one end, 1/2" NPT male stainless steel on the other.

With that said Terry, how does one seal PVC/CPVC threads correctly with teflon tape such as this? https://www.harborfreight.com/12-in-x-43-12-ft-plumbers-thread-seal-tape-10-pk-61377.html
With all of the misinformation running rampant about how to do so correctly, it would be a BIG help to those new to plumbing to have the forum admin weigh in with his knowledge on a time-tested and proven method that produces consistent results.

If this were a Mazda RX-7 and someone asked about charging problems, I would refer them to the article I wrote years ago, detailing the first three mods all new owners need to do.
A: Alternator (92-95 Ford Taurus 3.8L one)
B: Battery Terminals (Marine Battery Terminals)
C: Cables (DIY soldered 4awg welding cable)

They're all cheap to do and it makes a world of difference.

Reach4, while I'm not one for taking shortcuts to save time/money, 6-8 turns of teflon tape PLUS pipe joint compound (Rectorseal T plus 2). sounds like an excessive amount from a newb's perspective, especially for an interference fit junction with plastic threads like this. Could you please clarify the reasoning for this?
 

Reach4

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PVC female fitting + PVC male fitting = Good
Not so good. This can work if the female is extra strong. The female couplers for well work should be schedule 120, which is extra heavy. Plus the people using them will be experienced enough to get the torque right.

Brass female fitting + PVC male fitting = OK, not ideal (male threads can be sheared if overtorqued)
Good... IMO, overtorquing is no less likely to break a pvc male thread into pvc than into brass, unless we presume that the female thread breaking first would save the male. I think that is not what you are thinking.
 

Akagis_white_comet

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On today's adventure in plumbing, here we are back at the house. I got some transition male adapters and another bag of regular CPVC male adapters to make some nipples with CPVC threads on one end, stainless steel on the other. Nipple to Sink hose leaks all solved :)

Now comes Phase 2: fixing all the ****ing leaks. While swapping the brass nipples out for the CPVC to Stainless ones, each of the affected joints were wrapped with 3-4 turns of white teflon tape from Harbor freight and threaded in 6-7 turns total. This worked on every joint throughout the bathroom, with exception to the water heater. Since those leaks could be associated with the brass nipples being overtorqued, I just tagged them for later and moved forward to the kitchen.

Now onto the kitchen. Repeated the same process...and it leaks.

While waiting for answers, I found a handy chart from www.surpluscenter.com for torque (finger tight plus turns AND Ft.lbs), thread engagement and proper number of wraps of teflon tape.

Please note that the teflon tape I have is oddly not transparent as one would expect from a discount retailer. I had a roll from an unknown source and could see my fingers through it. It went into the trash as a precaution. The stuff from HF is the good stuff.

I'm getting VERY tired of leaks randomly sprouting up for no reason that i can discern. For example, a NEW faucet worked fine yesterday and now it leaks from its outlet...:confused::confused::mad::mad:

help
 

Terry

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I often do three wraps of tape and then coat over that with thread sealant. (pipe dope)
There is no formula for how many turns they go in. All threads are a little different.
If there is a rubber washer making the seal, then tape should not be used, as a little strand can lay over the washer and allow a gap for water to get through. Tape is only for tapered joints with an interference fit.
 

Jadnashua

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If the male and female threads were perfect, you might get by with a prescribed number of turns, but in reality, that almost never happens. Some fittings aren't made to specs, or the tap or die was not sharp and tore things, or was out of specs.
 

Akagis_white_comet

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Here is the chart I was referring to: https://www.surpluscenter.com/images/techhelp/NPT.pdf

I'm well aware of how manufacturing variances can affect the end result of number of turns or final torque. What I'm looking for is a baseline set of values to start with, and THEN add in the variables. It's more conducive to learning this way.

Terry, thank you or clarifying about the Teflon tape meeting Sink Hose end seal. I had a feeling about this and played it safe by leaving the first couple threads untaped. No leaks :)
 
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