Leaking NPT swivel connections

I assume my problem is because the seal of an NPT swivel connection depends on the machine fit between the chamfer in the female fitting and the "cone" in the male fitting.

I've got four NPT swivel elbows and two NPT straight swivels on my joystick valve and they ALL leak. No matter how tight I tighten them. They are TIGHT, no wiggle or swivel whatsoever, but they still leak.

Took them apart, can't see anything wrong, no burrs or anything like that. Tried teflon tape on the threads even though it's not leaking around the threads. Obviously that didn't work.

Before I go and spend another two hundred dollars on JIC adapters, are there any tricks to getting these to seal?

They make special copper washers to seal inside flare. I have also used leak lock sealant on flare fitting with good success..

The male NPT has to have the 30 degree seat to seal, not all of them are 30 degree but the fitting might be stamped 30
degree or may have a tag on it when purchased new. If no markings on the existing fittings or if in doubt you could buy one
male fitting that is for sure 30 degree seat and if it does not leak that should tell the tale.

(quoted from post at 10:25:10 03/27/23) I assume my problem is because the seal of an NPT swivel connection depends on the machine fit between the chamfer in the female fitting and the "cone" in the male fitting.

I've got four NPT swivel elbows and two NPT straight swivels on my joystick valve and they ALL leak. No matter how tight I tighten them. They are TIGHT, no wiggle or swivel whatsoever, but they still leak.

Took them apart, can't see anything wrong, no burrs or anything like that. Tried teflon tape on the threads even though it's not leaking around the threads. Obviously that didn't work.

Before I go and spend another two hundred dollars on JIC adapters, are there any tricks to getting these to seal?

Click to expand...

I am thinking these are adapters threaded into the valve body to connect the hoses to. I would agree with your assumption that the mating tapered area, of the hoses you are connecting into the swivels, do not match the taper of the swivel adapter. I have encountered that, most often when mating to older hoses. They look ok, but won't seal. I either replaced the hose or added a new rigid adapter to the hose that sealed on the threads, with the right chamfer to match the swivel adapter seat. Likely not your issue, unless somewhere fittings got mixed up, but some BSPT and BSPP will thread into NPT, and vice versa, but not seal.

(quoted from post at 10:25:10 03/27/23) I assume my problem is because the seal of an NPT swivel connection depends on the machine fit between the chamfer in the female fitting and the "cone" in the male fitting.

I've got four NPT swivel elbows and two NPT straight swivels on my joystick valve and they ALL leak. No matter how tight I tighten them. They are TIGHT, no wiggle or swivel whatsoever, but they still leak.

Took them apart, can't see anything wrong, no burrs or anything like that. Tried teflon tape on the threads even though it's not leaking around the threads. Obviously that didn't work.

Before I go and spend another two hundred dollars on JIC adapters, are there any tricks to getting these to seal?

Click to expand...

There are no "tricks" to getting hydraulic NPT fittings to seal, unless you are dealing with "black pipe" style NPT fittings, such as straight connectors, bushing, couplings, etc, as most of these don't have the taper incorporated in them. In these cases a sealant such as pipe dope must be used. These type of NPT connections are not leakproof without pipe dope. As you had said, the seal on other hydraulic NPT fitting is on the taper. Both male and female must be "hydraulic" NPT with the tapers. If one fitting is standard "black pipe" NPT, they won't seal no matter what, as a lot of these don't have the proper taper. Obviously "black pipe" NPT should not be used on the high pressure side of hydraulics, as they are not rated for the pressure. As you mentioned, once the fitting stops swiveling, (unless a "live" swivel), the connection is tight and should not leak.

You mention:

.... machine fit between the chamfer in the female fitting and the "cone" in the male fitting

Click to expand...

A typical connection on a hydraulic NPT swivel 90 or straight, is a hydraulic hose male npt to the female NPT fitting. In this case the male NPT hose has the "chamfer" and the female fitting has the "cone". If this is what you have, and they leak, one part or the other is faulty.
Note that some "older" NPT hydraulic hoses, are "black pipe" style, that is no chamfer. As said previously those won't seal no matter what.

they are leaking at the swivel not the connection. at least thats where i have always had them leak. there is no fix.

These are all new modern hoses and fittings all purchased from the same hydraulic shop, they are NPT with tapered thread, and yes, they are leaking around the swivel not through the threads.

might want to find out what make yours are then look for another supplier. same sort of deal with a cheap open end wrench as compared to a
high quality one.

So, just to be clear... The fittings are not leaking around the thread area? If this is correct, your issue is not NPT sealing.
Sounds a bit like the swivel joints are leaking. Is there any way the assembly can be put together without swivel joints? We have
a remote on a Ford that had leaking swivels. I figured out how to assemble it without swivels, and the problem is gone. Still NPT
though. I use the yellow teflon tape on oil and fuel NPT connections. Just be certain to keep the tape backed off the front nose
of the male connection a bit, so none of it can get into the system.

If these are the fittings with swivels that come tight when tightened up and leak the swivel is defective. If new hoses I would take them back and have them redo them under a warranty if they have any. If they are the swivel that still swivels after they are tight they are bad in the swivel and need new hoses. IF they are new hoses agin I would take them back and have them redo the job with different swivels. I don't have much problem with the swivels that comes tight when tightened up. Usually get a cracked or bent fitting that lets it leak.

Correctly mated swivel fittings will not leak unless cracked or badly gouged. Note the note... you can use a regular NPT male but it MUST have the 30 degree chamfer.




This post was edited by WilBury on 03/28/2023 at 04:50 am.

(quoted from post at 10:14:22 03/27/23) So, just to be clear... The fittings are not leaking around the thread area? If this is correct, your issue is not NPT sealing.
Sounds a bit like the swivel joints are leaking. Is there any way the assembly can be put together without swivel joints? We have
a remote on a Ford that had leaking swivels. I figured out how to assemble it without swivels, and the problem is gone. Still NPT
though. I use the yellow teflon tape on oil and fuel NPT connections. Just be certain to keep the tape backed off the front nose
of the male connection a bit, so none of it can get into the system.

Click to expand...

Correct. The fittings are leaking around the swivel.

There is no way they can be put together without swivels. This is on the body of a joystick valve with the 4 work ports all in a cluster. There is no way to spin more than one elbow in without swivels.

My mistake was going from BSPP to NPT instead of BSPP to JIC, then a JIC to NPT elbow for the coupler.

I figured the fittings were all new from the same supplier, so what could go wrong?

If you have a non swivel npt fitting crimped to your hose, then
use a M-F npt swivel adapter it should last a whole lot better
than a swivel end crimped to the hose.