How tight should a threaded PVC fitting be?
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Old 10-07-2009, 02:22 PM   #1
Harry Muscle
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How tight should a threaded PVC fitting be?


Does anyone know officially (for example as per the plumbing code) how tight a threaded PVC fitting should be? I'm guessing it's hand tighten + X number of turns.

Thanks,
Harry
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Old 10-07-2009, 03:30 PM   #2
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I dont know the code but I use teflon tape and a wrench.
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Old 10-07-2009, 03:58 PM   #3
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I have no idea what the torque spec on these is, or if it's even specified like that. But I have seen instructions that say "turn until it doesn't leak anymore". You do not want to over tighten a pipe thread...
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Old 10-07-2009, 05:36 PM   #4
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Teflon tape isn't a good idea on PVC threaded fittings, according to the fitting manufacturers. The primary purpose of teflon tape is to lubricate the treads so the fitting can tighten further with less effort, and that leads to breaking the PVC female fittings. Instead, the use of thread joint compound, a paste, which is made for use on PVC pipe, is recommended. Then notice that most PVC pipe thread connections don't have wrench flats or they have minimal wrench flats. That means they are not intended to be tightened with crescent wrenches, for example. Instead, tighten them by hand, plus a little with a wrench or adjustable pliers (not recommended by the manufacturers, but it works.) You have to get a feel for what the right torque is, judging by what you have found makes a non-leaking connection. It doesn't take long to learn what too much torque is, but the fittings are cheap, so replacing the broken ones isn't that big a deal.
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Old 10-07-2009, 06:33 PM   #5
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yea my basic rules, as i stand in the aisles of Home Depot, is just buy 3 of every fitting. One to break, one to test, and one to hopefully finally work. haha.
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Old 10-07-2009, 10:12 PM   #6
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Quote:
Originally Posted by Hoppy View Post
Teflon tape isn't a good idea on PVC threaded fittings, according to the fitting manufacturers. The primary purpose of teflon tape is to lubricate the treads so the fitting can tighten further with less effort, and that leads to breaking the PVC female fittings. Instead, the use of thread joint compound, a paste, which is made for use on PVC pipe, is recommended.
That's correct.

You have to be especially careful with female PVC fittings. Since U.S. pipe fittings are tapered, the male fitting can act like a wedge, and split the female fitting. BTDT.

As a general rule, I never use a metal male fitting with a PVC female fitting, and like to avoid PVC female fittings. When I do use one (with a plastic male fitting), I use paste, and about one turn past hand-tight.
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Old 10-07-2009, 11:11 PM   #7
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Hoppy is right. It just has to be water tight. With 'pipe dope' you can get this. You also have to remember that you're working with maybe a 10 lbs. psi max with pumps, filters,etc.
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Old 10-08-2009, 04:02 PM   #8
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Also, the fittings use National Pipe Thread standard. This thread type tapers, so that the joint gets tighter the more revolutions. It should not require more than a 1/4 to 1/2 turn past the hand tight point to seal a pipe for aquarium use.

EDIT -- I found this on LASCOs site. They say no more than 2 turns past finger tight.

http://www.lascofittings.com/support...dedPlastic.asp

Last edited by BG1772; 10-08-2009 at 04:09 PM.. Reason: more information
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Old 10-08-2009, 04:33 PM   #9
Harry Muscle
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Quote:
Originally Posted by BG1772 View Post
Also, the fittings use National Pipe Thread standard. This thread type tapers, so that the joint gets tighter the more revolutions. It should not require more than a 1/4 to 1/2 turn past the hand tight point to seal a pipe for aquarium use.

EDIT -- I found this on LASCOs site. They say no more than 2 turns past finger tight.

http://www.lascofittings.com/support...dedPlastic.asp
Very interesting link.

Thanks,
Harry
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