Plumbing Parts - Pipe Threads

[FearTheTerps]

So I'm working on the plumbing for my fuge and cant get my pieces to fit together( See Pic Below). I am attaching a hose barb fitting to a pvc fitting. The pieces start to thread together, but after a full turn or 2 it gets so tight that I cant tighten the pieces anymore. This is just a dry fit, I havent used any silicone grease or teflon tape yet. If I cant even get it to dry fit I dont see how I can tighten it with the tape wraped around. The hose barb fitting is national pipe thread, and the the pvc piece say just female pipe thread. Im pretty sure I am correct, but isnt female NPT the same as FPT????

 

I've used these fittings before, but mostly for water change pumps where a small leak is a big a deal. I've also used them in one of my sumps before, but the fitting was inside the tank so I didnt care if it leaked either. On my new installation the hose barb fitting will be in a place where a leak would be a very bad bad thing.

 

 

Is the threading different? If I use silicone grease will it make a difference? Something I am missing?

 

[L8 2 RISE]

This is normal, get new parts or use a vice and a pipe wrench.

[Noobalicious]

is that a schedule 80 being screwed into a schedule 40?

[Origami]

The "T" in NPT is for "tapered" and will typically get tighter as you tighten it (rather than bottoming out). This helps to seal the connection more quickly and is, as Sam observed, normal. If you get some pipe joint compound (search for it at Lowe's), it should tighten smoothly and seal very nicely. While tape is cleaner, I've never had a joint leak where I've properly applied joint compound.

[FearTheTerps]

I used the joint compound before and did have a small leak, but I only used a pair of pliers to tighten it. It didnt help with making the threading any easier if I recall correctly. Thats why I was planning on using the tape this time, plus I was using tape for my bulkhead threads.

 

Hey Steve, long time no see, welcome back. I wouldnt think the schedule would have anything to do with the thread size. The white piece is sch 40, not sure if the hose barb even has a schedule rating.

Edited March 15, 2011 by FearTheTerps

[OUsnakebyte]

Be careful tightening those fittings down too far with a wrench. I've had the female fittings that you have pictured spilt before and cause a leak. It didn't happen right away - took a few weeks but it eventually spilt.

 

Cheers

Mike

[Integral9]

Whatever you use (tape or compound) I think as long as you get a few turns on the connection it should seal properly. Hardly anything fits perfectly these days and over tightening could make it never seal properly. So I would just hand tighten it as best you can and then put an extra turn on it with a wrench. Beyond that and you could bust the connection, like OUsnakebyte said.

[FearTheTerps]

Using the teflon tape really helped. I was able to put the hose barb in much farther then I could when I did the dry fit.

 

Leak test will probably come tomorrow, got some vball to play tonite.