how do I get my NPT connections to not leak

[GC1710]

I use teflon tape and torque the crap out of hydraulic NPT fittings. (now don't use tape nor torque the crap out of SAE o-ring or JIC) but for NPT I find nothing works better than teflon tape (wrapped in the direction of the threads (so when you tighten you don't unravel the tape)).

Just made over a dozen NPT connections and none leaked using this method.

 

[DieselBound]

Locktite 242, that's the response I got when I asked this question of a major hydraulic's vendor (here on this site). Since no threads are perfect (some are, of course, manufactured to a better tolerance than others) a sealer aids in filling in minor distortions.

Dry-thread to test how well the parts mate up (better to find out if you've got some binding [bad threads] before you get parts "gooped" up).
Clean/dry.
Apply sealant.
Tighten well and monitor.
Re-tighten if needed.

And, for hoses, make sure to NOT bend improperly (past allowable radius- resting and throughout operative range), especially right next to a connector/fitting.

 

[Gary Fowler]

It sounds counter intuitive, but it is possible to over tighten these fittings and distort the threads. Its better to tighten them just a little snug, then tighten just a little more at a time if they happen to leak.

You are spot on. Most leaks in threaded pipe occur from overtightening. This is assuming that you have good threads to start with. A good lubricant is essential in either paste or tape form. Either when done correctly will not contaminate your oil (or whatever fluid) upon first use. Subsequent removal will require complete removal of the tape that is embedded in the threads prior to re-installation.

If you are using 1/2"-1.5" pipe, a 12" pipe wrench is large enough to tighten sufficiently using medium strength of a young man or maybe most of the strength of an old man. Anything more is likely damaging the threads. When fully tightened a threaded joint should still be showing about 1-1.5 threads on the male joint. Smaller pipe requires less torque to tighten so be careful not to overtighten.

As KYErik says, you can always tighten a bit more, but you cant untighten a stripped thread.

 

[CCWKen]

It's simple. Don't use NPT for hydraulics.

 

[ericm979]

It's simple. Don't use NPT for hydraulics.

I wish that was an option. But for some reason a lot of hydraulic things come in NPT only, or the largest selection is NPT.

 

[Oldpath05]

Wow, lots of good suggestions. Many conflicting but that's the internet for you.
These connections are to things that only come in NPT, like quick couplers and valves. I've been using NPT to JIC adaptors and then JIC where I'm the one deciding what coupling to use. It's the NPT side of the NPT to JIC adaptors that I'm having trouble with. I replaced one on a quick coupler using a new adaptor and quick coupler and let it sit 24 hours and it's now good. One on a valve still leaks and it'll be the second time I've redone it. I don't have new parts for that one but this time I'll clean it with brake cleaner and let it sit a day before putting pressure on it. I may try loctite.

I agree with the WOW factor. I thought if teflon tape was wrapped around threads right it wont get in to valve bodys, same as if the pipe sealant is not use right, that might also end up in somewhere.

What I like about teflon tape is no special cleaning on the fitting from the oil on the threads and or making sure it's perfectly dry with my helpers shirt, just wrap the tape around the right way and throw it together.

But since I'm open to new ideas I might try this stuff next time the hydraulic hose breaks>>> Amazon.com: Rectorseal 25631 4-Ounce No. 5 Pipe Thread Sealant: Home & Kitchen

 

[DieselBound]

Tape is perfectly fine as long as you know how to apply it (keep it off the end threads- and if disassembling be sure none is inside any female end). The liquid stuff if misapplied won't cause any problems, so it's basically idiot-proof. I seem to struggle with pipe stuff. Took me a long time to get water plumbing down correctly. Had a lot of leaks with hoses to my rear remotes, but am hoping that I've got things taken care of now (I tend to under-tighten, fearing problems from over-tightening).

 

[Billrog]

I agree with using Teflon tape ( keep in mind there are more than 1 type) used keeping from the ends and you don't have to let it set before use . Oldpath keep in mind though I'm sure it will work most of the reviews were for low pressure gas for hydraulic applications I would snug up the joint and let it set for a few hrs.or more.

 

[tcreeley]

A replacement I did back in 2014. I used plain old PTFE teflon tape. I used 21/2 wraps and kept it back up from the first two threads on the male end of the hose, and I screwed on the adapter. Finger tight, grip tight (wrench), and then a little extra. I pulled the new leaky hose off and put this one on - no leaks.
The thread sealer paste did not work for me.
Been 3 years - all is good.

 

[Dave M7040]

How do you make NPT connections that don't leak? Too many of the ones I added recently leak. I have been using permatex liquid PTFE sealer.

First, if we are talking hydraulic systems, DO NOT use plumbing fittings.

Hydraulic fittings are steel not iron and although the plumbing fitting will connect, it can distort, crack and create very dangerous high pressure fluid leaks.

Pipe threads can be tapered or straight. Most people don't know of straight pipe threads.

NPS = National Pipe Straight
NPT = National Pipe Thread

Both NPT and NPS have the same thread angle, shape, and pitch (threads per inch). However, NPT threads are tapered and NPS threads are straight (parallel). Both threads have a 60ｰ included angle and have flat peaks and valleys.

Tapered Pipe Thread is commonly found on ends of pipe, nipples and fittings (i.e. couplings, elbows, tees, etc.). Note: Sharply angled threads are very critical to joint being tight with no leaks. Thread sealant or tape is typically required to complete the seal.
Straight Pipe Threads need a gasket or O-ring to create a seal.

While NPT and NPS threads will engage, they do not seal properly with each other.

Tell us more about the situation(s) were this recurring leak is happening, perhaps even a photo or two.

Properly selected and properly used pipe threads should not be leaking nor hard to get to seal.

Sometimes, owners unfamiliar with serious hydraulic systems, are trying to seal joints using pipe dope or teflon when in reality the joint it meant to be one metal surface seating on another metal surface.

Automotive hydraulic brake lines are an example of this metal to metal design where a double flare is used. Propane lines using flexible copper use a single flare to seat against a metal fitting with a tapered face.

These are all lessons I had to learn the hard way over many years so I understand the confusion that can occur.

Dave M7040