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Old 04-18-2019, 01:37 PM   #21
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Originally Posted by Bytesponge View Post
The yellow tape or sealant designed for Gas lines can be used on the threaded portion of the flare fitting but not required on the flare which is designed to be self-sealing. Probably over kill but will not affect sealing as long as the sealant or tape doesn't obstruct I.D. of plumbing and plug regulator or orifices further down the line.
IMHO
The only purpose of PTFE tape in plumbing is as a sealant for tapered threads. Thatís it. PTFE tape serves no purpose on the threads of a flared fitting or any other fitting with straight threads. With plumbing, if you run across anything that uses straight threads, there is something else, such as a gasket, flare, ferrule or washer to serve the purpose of sealing the joint ó just as with a flared fitting ó the straight threads are there to get the flared nut up to the flare to tighten the flare to make the seal. The straight threads on a compression fitting are there to get the nut up to the compression fitting and compress the ferrule which makes the seal. Putting PTFE tape on straight threads can stress the threads and cause them to expand the joint resulting in failure. The more PTFE tape used, the higher the chances are of causing a problem.

Many handymen and homeowners are under the impression that ďif itís got threads, it needs Teflon tape. What can it hurt?Ē

Again...with plumbing, the only place you are supposed to use PTFE tape is on tapered threads.

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Old 04-18-2019, 03:57 PM   #22
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PTFE tape

Nomad, glad you set them straight. Iíve seem folks that put tape on the ground joint threads of a union. Bad, bad, bad. Still wonít end it being done though. Again, good answer!
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Old 04-18-2019, 07:07 PM   #23
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Do you also know why the gas lines nut is plastic.
Because when you have a fire it melts and shuts off the flow of gas.
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Old 04-19-2019, 05:10 AM   #24
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Originally Posted by Waterops1 View Post
Nomad, glad you set them straight. Iíve seem folks that put tape on the ground joint threads of a union. Bad, bad, bad. Still wonít end it being done though. Again, good answer!
I have seen this, too. I have also seen pipe dope used on union ground joints and flares. I have seen this done by plumbers as well as those who donít know any better. Plumbers will use tape and dope on a union or flare that wonít seal, no matter how much they tighten it, just so they can be done with the problem...for now. Tape and dope will very often stop that pesky little leak long enough to hold a test for an inspection or to give a customer the perception that everything is good, but the leak will usually return later ó who knows when? Maybe in a couple of hours, or maybe after a couple of years ó but it will return, and it could be disastrous. Itís not worth doing things the wrong way, especially when you could be putting othersí property and lives at risk.

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Old 04-20-2019, 06:32 AM   #25
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The stoppage of flow is actually caused by a device inside the big green nut.
It has TWO protection devices built into it.

One... you sorta touched on and that is the plunger that pushes open the recessed valve in the OPD. (on the tank) There is a thermal sensitive bushing inside the green nut which will melt at about +-240ļ. When the bushing melts, (due to a fire) the plunger springs back and closes the valve in the OPD (on the tank) even if the service valve is in the open position.

The second safety device in the big green nut is the "flow-limiting-device."
Every time the cylinder valve is opened, a small ball in the center of the brass nipple (inside the green nut) is pushed forward into a brass seat. This seat doesnít totally shut off the gas.

By design, it allows a small amount of gas (by-pass flow) to go into the RVís gas system. If everything in the gas system is closed and in the off position AND if there are no leaks, the by-pass flow builds up a back pressure that equalizes the pressure which then allows unrestricted flow through the system.

If the cylinder valve is opened when the propane lines are completely empty or there is a severed line, the ball can't equalize and the system shuts down. The by-pass flow will not equalize until some propane gets into the system or a leak is found and fixed.

To rectify, turn the valve off at the tank, make sure everything is closed and at the off position, wait about 15 seconds. If the system is closed and tight, (no leaks, nothing left on) the back pressure builds up, equalizes the pressure and feeds unrestricted gas flow for normal operation.

OK, that makes sense then. I didn't know that the excess flow limiter was in the big green nut. Learn something new every day!



Thanks for the info!! I stand corrected Also learned why the RV pigtails are green... they allow higher flow than the black nuts.
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Old 04-20-2019, 07:06 PM   #26
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Originally Posted by 5picker View Post
The stoppage of flow is actually caused by a device inside the big green nut.
It has TWO protection devices built into it.

One... you sorta touched on and that is the plunger that pushes open the recessed valve in the OPD. (on the tank) There is a thermal sensitive bushing inside the green nut which will melt at about +-240ļ. When the bushing melts, (due to a fire) the plunger springs back and closes the valve in the OPD (on the tank) even if the service valve is in the open position.

The second safety device in the big green nut is the "flow-limiting-device."
Every time the cylinder valve is opened, a small ball in the center of the brass nipple (inside the green nut) is pushed forward into a brass seat. This seat doesnít totally shut off the gas.

By design, it allows a small amount of gas (by-pass flow) to go into the RVís gas system. If everything in the gas system is closed and in the off position AND if there are no leaks, the by-pass flow builds up a back pressure that equalizes the pressure which then allows unrestricted flow through the system.

If the cylinder valve is opened when the propane lines are completely empty or there is a severed line, the ball can't equalize and the system shuts down. The by-pass flow will not equalize until some propane gets into the system or a leak is found and fixed.

To rectify, turn the valve off at the tank, make sure everything is closed and at the off position, wait about 15 seconds. If the system is closed and tight, (no leaks, nothing left on) the back pressure builds up, equalizes the pressure and feeds unrestricted gas flow for normal operation.
Good explanation 5picker.
How about the ones with a big red nut? Are there any safety features with those?
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Old 04-22-2019, 12:44 PM   #27
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Good explanation 5picker.
How about the ones with a big red nut? Are there any safety features with those?
Sorry, I missed this question.

Yes, the red ACME nuts have flow and thermal protection but are rated for full flow over 400,000 BTUs/hour.

The dark green around 400,000 BTU/hour, the light green around 200,000 BTU/hour and the black 100,000 BTU/hour and less. Flow rates seem to vary between manufacturers.
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