threaded pvc question

[Peeley]

I have a newbie question that hopefully has an easy answer. I heard it was nigh impossible to hand tighten threaded pvc that was 1+". I have 3/4" pvc and i still cant close the gap... I have teflon tape, maybe im using it wrong (wrapped it once around the male threads)? Is there a trick? Can I trim off the end?

 

[Anonymous]

The threads are tapered.

There's two spec's for threads, one is tapered, and one is straight. (too lazy to go find the actual names right now.) Most PVC is tapered, so you can't close the gap.

When trying to make a 1/2" PVC outlet for an overflow box, I had to make 'washers' from a scrap piece of acrylic.


HTH
B

 

[Peeley]

Thanks Bingo.
i ended up doing something like that. I glued another piece of acrylic to the bottom of the box so it would be thicker and redrilled my holes.
In the time since my post i learned that the grey pipes (not sure what the term is) fit together more loosely. maybe those are the untapered ones you are referring to?

 

[Anonymous]

The grey pipe is for landscaping usage. They are identical to common pipe thread (NPT-National Pipe Thread) in that it is tapered. Non-tapered thread does not have NPT designation.

If the thread is too long, and the female end is not deep enough, cutting off the male end (sorry about the wording.... ) may helps. But since it is taper, most likely, it won't make it goes in any deeper, unless you want to burst the female side.

 

[jcurry@wesketch]

Just wrap the teflon tape around the male threads 4 or 5 times or more as needed. But make sure you wrap the tape in the opposite direction that you need to screw in the MPT.

J

 

[Anonymous]

I thought one should wrap the teflon tape in the same direction as the thread on the pipe? :?

 

[jcurry@wesketch]

I guess it depends on how you look at it, "opposite the screw in direction" or "with the threads" is the same thing.

 

[jdieck]

If by closing the gap you mean thread in the whole threded lenght it will not happen as mentioned before the thread is tapered to improve the sealing.

The threads on PVC fittings are not cut but molded so a hairline on the thread forms due to the mold and sometimes this make it difficult for the thread to seal or it get's stuck bfore the thread reaches the sealing point.
To improve the ease of threading in addition to the teflon tape I use teflon paste, this improves the seal and lubricates the thread. You just need to use a little.
With the threaded end pointing towards you, wrap the tape clockwise starting from the outer thread and overlaping half the width with each turn until about 3/4 of the threadd is covered. Use your nail to drive the tape into the threads and then apply a small coat of TFE paste on top of the tape and thread by hand as far as it goes. Use a band (belt) wrench (You may need two wrenches) to tighten 1/2 a turn more. No leaks this way.