Help with simple plumbing question - how tight should it be?

February 4, 2013 11:20 PM

Installing a new dishwasher, and the elbow fitting that connects the hot water hose to the dishwasher ends up facing the wrong direction when tightened as far as it will go by hand. How many more times should I turn it with a wrench?

I'm installing a new Bosch dishwasher to replace our old leaky one, and I'm feeling good about all of it except for this one part. The 90 degree fitting which connects the hot water line to the dishwasher only turns about 2 times around when screwed in by hand, and then ends up facing the wrong direction for the water hose. It needs to turn another 180 degrees to face the right way. I haven't taken a wrench to it yet, because in reading online, some people are saying that once it is finger tight, it should go another 2 rotations with a wrench. This seems like an awful lot to me. Initially I thought that turning it the 180 degrees with a wrench seemed like it might be too much, but now I'm not so sure. My main concern is that I don't want it to leak, since that was the problem before which caused me a lot of time and money to fix.

The part says it is an NPT fitting, and I believe they are brass.

So, am I OK to turn it the 180 degrees with a wrench? Should I be giving it an additional rotation? I don't want to break the dishwasher, but I also don't want any leaks. I will be using several rotations of teflon tape.

posted by markblasco to home & garden (6 answers total)

1/2 turn on an NPT fitting is fine, usually with black pipe you can do more, but I'm wary of stress corrision cracking with brass fittings as I see that failure mode a lot at work.
posted by sanka at 12:00 AM on February 5

I always go by feel rather than counting rotations. Using an appropriately sized wrench for the fitting, (in your case probably something 4-6" long), you'll feel the resistance increase as the fitting goes around -- gradually at first, then more sharply. It isn't easy to overtighten unless you're using a much bigger wrench than is needed.

I agree with Sanka; your 180 degrees past finger-tight will be no problem at all. It wouldn't surprise me at all if you have to then go another full rotation before the connection really firms up.

My main concern is that I don't want it to leak, since that was the problem before which caused me a lot of time and money to fix.

It would be very unusual for this connection to leak; usually it's the hose itself that fails. If it's not leaking within a few minutes after you turn the water back on, you're almost certainly fine.

Don't go crazy with the Teflon tape; it's not chocolate, and more than enough is not better. For small fittings like this I usually go around twice, with a bit extra for overlap.
posted by jon1270 at 1:29 AM on February 5

Also, it sounds like you've been test-fitting things without the Teflon tape. If that's so, then you don't yet know where finger-tight will be, because the tape both acts as a lubricant and takes up space in the threads.

I suggest you turn it to finger tight, then use the wrench to move it around to the direction you need it to point in. If it's still turning easily when you get to that position, go around again.

Note: if you go a smidge too far, take it completely apart, apply new tape and start over. You can't adjust the position of NPT connections by going backwards.
posted by jon1270 at 1:56 AM on February 5

one thing that might help is to provide color on finger tight. this does NOT mean "as tight as you can get it with your fingers" from my experience. it means lightly tightened with your fingers. meaning. if you used all your might to get it to that position then CAREFULLY turn it the extra 180 if you can without forcing it and you'd be fine. the 2 turns thing is a GUIDE not a rule.

also, seconding the comment about teflon tape. if you dont have the tape on right now while you test fit this will make the overall fit a little tighter.

a little my personal experience (just installed a dishawasher a few months ago) was that the 90 degree elbow turner several times before finger tight, not just 2x so PLEASE BE CAREFUL that you don't have it cross threaded. Just get it turned to how common sense suggests (IE dont crank it down) and turn the water on. if it leaks you can tighten a little more (even 1/8 turn can often seal a leak) but if you have OVERTIGHTENED it you can go LOOSER to fix the leak. if you don't have it quite tight enough you will see a drible or a tiny stream, not a gushing torrent (if there IS a gushing torrent then its likely crossthreaded) so experimentation is ok. when i did mine, i basically got it how i thought it was right, turned the water on and then tightened it a bit more to fix a weap. then i laid a single flat sheet of newspaper under it and checked the paper for a week which showed no signs of a leak.

good luck.
posted by chasles at 4:45 AM on February 5

One of the best ways to avoid cross threading is to turn the nut backwards until it fits, and then turn it the right.

Teflon tape. You are using that too I hope.
posted by mearls at 7:10 AM on February 5

Thanks for the comments. I did use tape when I tested the fit. I don't think it's cross threaded, since it went on easily and looked straight, and I put it on several times without the tape when test fitting things, and it always turned exactly the same amount. I never had to force anything to get it to turn.

I'll turn it the 180 degrees when I do the full install tonight, and if it seems loose I'll try going further.
posted by markblasco at 7:25 AM on February 5