Hydraulic fittings leaking, what am I doing wrong?

[Nicfin36]

OK, I have two hydraulic elbow fittings that leak. They are 3/8 NPSM female with the o-ring inside going to a 3/8 NPT male. I have the same configuration on another line with no leaks. I tightened them twice, but still leaking. I understand/read that sealant is not needed on the NPSM due to the O-ring seal and did not use any on these or the other two not leaking. Should I try sealant on the threads? Arrow is the NPSM nut where the fluid is leaking.

 

[eserv]

OK, I have two hydraulic elbow fittings that leak. They are 3/8 NPSM female with the o-ring inside going to a 3/8 NPT male. I have the same configuration on another line with no leaks. I tightened them twice, but still leaking. I understand/read that sealant is not needed on the NPSM due to the O-ring seal and did not use any on these or the other two not leaking. Should I try sealant on the threads? Arrow is the NPSM nut where the fluid is leaking.




View attachment 64365

Do the male fittings have a taper to fit up to the npsm fitting?

 

[Nicfin36]

Do the male fittings have a taper to fit up to the npsm fitting?

The male fitting came with the cylinder and is an adapter that converts from 3/8 BSSP (British) The website just says 3/8 NPT male. You think it is straight walled?

 

[eserv]

The male fitting came with the cylinder and is an adapter that converts from 3/8 BSSP (British) The website just says 3/8 NPT male. You think it is straight walled?

Look at the end of the male pipe fitting, it should have a taper that fits the taper inside the female swivel. If it is flat the chances of it sealing no matter what you do are really poor

 

[MOOTS]

OK, I have two hydraulic elbow fittings that leak. They are 3/8 NPSM female with the o-ring inside going to a 3/8 NPT male. I have the same configuration on another line with no leaks. I tightened them twice, but still leaking. I understand/read that sealant is not needed on the NPSM due to the O-ring seal and did not use any on these or the other two not leaking. Should I try sealant on the threads? Arrow is the NPSM nut where the fluid is leaking.




View attachment 64365

Are the adapters installed the right way?

 

[TheOldHokie]

OK, I have two hydraulic elbow fittings that leak. They are 3/8 NPSM female with the o-ring inside going to a 3/8 NPT male. I have the same configuration on another line with no leaks. I tightened them twice, but still leaking. I understand/read that sealant is not needed on the NPSM due to the O-ring seal and did not use any on these or the other two not leaking. Should I try sealant on the threads? Arrow is the NPSM nut where the fluid is leaking.




View attachment 64365

An NPSM swivel will not have an oring.

Dan

 

[eserv]

Look at the end of the male pipe fitting, it should have a taper that fits the taper inside the female swivel. If it is flat the chances of it sealing no matter what you do are really poor

NPSM (NATIONAL PIPE STRAIGHT MECHANICAL) Fittings

NPSM (NATIONAL PIPE STRAIGHT MECHANICAL) Female Pipe Swivel was designed to eliminate hose stress from twisting during assembly and reduce the number of different hose fittings required.

www.fittings.space

 

[Nicfin36]

Are the adapters installed the right way?

Probably not.

I can flip the elbow and try it that way,

An NPSM swivel will not have an oring.

Dan

I thought it had an o-ring down in there. Thanks for correcting that.

As, you can tell, I am very much a novice on hydraulic fittings.

Thanks for the help.

 

[TheOldHokie]

Probably not.

I can flip the elbow and try it that way,



I thought it had an o-ring down in there. Thanks for correcting that.

As, you can will tell, I am very much a novice on hydraulic fittings.

Thanks for the help.

A female NPSM swivel will have a male cone in the center. That will mate with a female conical seat on the end of the male fitting. The swivel simply clamps the conical surfaces together to effect the seal.

Dan

 

[Nicfin36]

OK, so I looked at the male end and it appeared to have a taper on the end. So, I decided to tighten the heck out of it, which I thought I had done, but I got down on both pretty good. I hooked it up to the tractor and ran it a bit. No leaks that I can see.

Thanks for all the help.

 

[Nicfin36]

Well, I checked later and saw some oil on the fitting threads, so I don't think I got it. I'm not hopeful, but I took the fittings off and put some thread sealant on the threads. I will see what happens later.

 

[DustyRusty]

NPT threads need some sealant on the threads, and be careful not to contaminate the inside of the fitting. On the thread itself, it will do no harm. When dealing with any fitting that uses an "O" ring, you should lubricate it with the hydraulic oil to avoid tearing the "O" ring when you tighten it.

 

[TheOldHokie]

Well, I checked later and saw some oil on the fitting threads, so I don't think I got it. I'm not hopeful, but I took the fittings off and put some thread sealant on the threads. I will see what happens later.

Here is a picture of the inside of a female pipe swivel and the end of a male NPT hydraulic fitting. Is this what you have? If so and it leaks there is something wrong with one or both fittings.

The raised conical seat in the center of the swivel matches the internal chamfer on the end of the pipe and is what makes the seal. If it leaks one or both of the sealing surfaces is damaged or improperly machined and the offending fitting(s) need to be replaced.

The swivel nut has NPSM (National Pipe Straight Mechanical) threads which are a very loose straight thread in the same pitch and nominal diameter as the NPT taper threads on the male component. The sole purpose of the threads in a pipe swivel connection is to facilitate assembly and clamp those two machined surfaces together to form a pressure tight joint. Putting thread sealant on a pipe swivel connection is never needed, and will not stop a hydraulic pressure leak.

Dan

 

[Nicfin36]

I haven't been ignoring y'all, just other stuff going on right now. I was planning to replace the elbow fittings with just straight ones from Tractor Supply and tilt the fitting assembly on the cyliner slightly, but both stores in my area are out of fittings. So, things will have to wait until I can buy some. Hokie, I will check the insides of the elbows. I think that is what they look like though. The culprit could be the adapter fitting on the cylinder that adapts the 3/8 British to 3/8 NPT.