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I've been ripping out the PB water line throughout my house and replacing with PEX and a bit of copper piping. However, the few threaded fittings each have very slow leaks.

Above the water tank I used 3/4 copper adapters. Above the water meter I used a 3/4 brass PEX adapter. Each were wrapped with two layers of white teflon tape clockwise. Then tightened as tight as possible with a crescent wrench (maybe 2 turns after hand tight). The washing machine adapters were wrench tightened at least 1 turn but stopped when they were properly aligned.

Looking around the web, I see many different opinions about why these type of connections get slow leaks.

  • Too much or too little tape (I've seen 2 to 20 wraps suggested)
  • Use joint compound instead of tape or use a compound with tape
  • Tighten so that only 1-2 threads are visible or tighten 1-2 turns after finger tight

So are there any standards for joining these connections?

Is it possible to over-tighten the fittings? (I'm worried about deforming the copper or cracking the brass)

The tape and compound seem to be for lubrication and not so much sealing, but many posts online suggest otherwise. This seems to affect the question of how much tape to use. Who's right?

Thanks!

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2 Answers 2

up vote 3 down vote accepted

See this thread about how much to tape to wrap. Two wraps might be too little while 20 seems pretty extreme.

Some people like tape, some like compound and some like both. I gave up on reading about which is better because it just seems to be a matter of opinion.

Both are for lubricating and sealing. The "Pipe Dope" has a substance in it (sometimes hemp) that expands with moisture to further help prevent leaks.

Regarding how tight, you can definitely over tighten but if they are leaking I wouldn't hesitate to give another bit of a turn. You need to be particularly careful with compression fittings since they can be more easily over-tightened.

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Most plumbers I work with use similar methods. On threaded connections with flair compression fittings, usually 3 to 4 wraps of teflon tape is good. Much more than that and it will bunch up and not work into the threads as tightened. On larger pipes, say 1" and larger, they often use tape on the male threads and a bit of joint compound on the female threads.

On sleeved tubing compression fittings and neoprene gasketed fittings (like for faucets, toilets etc.) no sealants are needed as all the sealing is done by the sleeves, not the threads.

As far as how tight a fitting needs to be: hand tight is never enough. On small compression fittings, hand tight then snug with a wrench, usually 1/2 to one turn. You can snug them up more after the water is turned on til any leaking stops. Do not overtighten any fitting before checking for leakage. You can always snug up a fitting, but you can't let off any tension without starting from the beginning or replacing a damaged fitting or pipe/tubing end. This is really important on small tubing and 1/2" copper.

After you do it right a few times, you will get a feel for it.

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