Connecting 1/2" NPTF

[LD1]

Hydraulic NPT fittings are not the same as normal NPT fittings. Only hydraulic NPT fittings should be used, not hardware NPT fittings.

If you examine a female fitting you will see there is an inner mating surface. Then on the male fittings you will see that the end is perfectly machined.

There is easy to find information on the difference with a simple Google search.

What you are describing is a npsm fitting. And those need no sealer (or lubrication as some say).

But there ARE hydraulic npt fittings that seal by the threads....not the inner cone

 

[jdmeth]

Hydraulic NPT fittings are not the same as normal NPT fittings. Only hydraulic NPT fittings should be used, not hardware NPT fittings.

If you examine a female fitting you will see there is an inner mating surface. Then on the male fittings you will see that the end is perfectly machined.

There is easy to find information on the difference with a simple Google search.

All I know is if we got hyfraulic hoses made up and put John Deere threaded plug in fittings on without tape they would leak. I got out of farming 25 years ago, things may be different now. Many implements we had used galvanized water pipe for runs to the cylinders. Never had one burst.

 

[WranglerX]

Obviously through this discussion there is a lot on misunderstanding about NPT fittings... Back to NPT VS NPTF

Understanding NPT, NPTF & NPS Thread Connections

Understanding NPT, NPTF & NPS Thread Connections - Learn more about various pipe fitting thread connections to ensure proper selection to create leak free seals.

www.buyfittingsonline.com

 

[rScotty]

I will catch some flack over this, but I never use tape. Too much chance of a bit coming loose and causing problems.
I only use the Teflon "dope" that comes in a tube and is available in most every big-box store.

You won't catch flack from me. After some 50 years of working on mechanical things I've gone to the dope over the tape. BTW, there are different types of dopes. Some of the fuel-resistant types of non-hardening dope are even better yet.
rScotty

 

[Oldtoad]

All I know is that teflon tape sure can gum up the works after being run through the pump, bypass controls, around the mulberry bush and back to the muffler bearings.
Thanks all.

 

[jdmeth]

All I know is that teflon tape sure can gum up the works after being run through the pump, bypass controls, around the mulberry bush and back to the muffler bearings.
Thanks all.

All my John Deeres had over 10,000 hours on them, not a minutes trouble with the hydraulic pump. Probably because Deere put a fine mesh screen on the suction pump located in the transmission. My 81 model 510 backhoe lost hydraulic pressure two yeas ago. The screen is removed by removing a plug in the lower side of the transmission. Yes, 10 gals of hydraulic oil comes out with it. 20 years of slime and gunk had it stopped up. My brother said he cleaned it once. Sprayed some brake cleaner through it, wiped it off with some paper towels and we were back in business.

 

[etpm]

All I know is that teflon tape sure can gum up the works after being run through the pump, bypass controls, around the mulberry bush and back to the muffler bearings.
Thanks all.

I replied to your original post with info about NPTF threads. Others posted with recommendations about different products for sealing. I mentioned that you might find galled threads after disassembling NPTF threads.
For sure teflon tape can gum up the works if applied incorrectly. I have found myself that Loctite paste and liquid thread sealing products are less likely to be applied incorrectly than teflon tape. It is a generic issue. I believe this is because it is so easy to get the tape too close to the end of the threads. People feel that they need to have that teflon tape applied right to the end of the thread. This tape then extrudes past the end of the threads when tightened and can then end up in the fluid. But when folks use some sort of paste or liquid thread sealant they seem to understand that it should not be applied so that it flows past the threads. Also, the paste and liquid sealants are not like pieces of tape that can clog stuff or prevent valves from sealing etc. because the tape is a solid.
My personal opinion is that whenever a tapered thread is used it should be used with either a thread with teflon tape or some sort of thread sealant. I like Loctite products the best but there others available that are just as good. And maybe better.
I use thread sealants and thread tape because it helps with preventing galling. This can affect sealing the first time the threaded components are assembled as well as any subsequent disassembling and reassembling. Galling is a serious issue and is a reason for many sealing failures of tapered threads.
The only drawback to anything that lubricates the threads is that the lubrication makes it easier to turn the threaded parts and can result in parts being over torqued.
Eric

 

[WranglerX]

The thing is one can prevent pieces of PTFE tape from coming lose and clogging system if you start the tape wrap leaving 1-2 thread bare at beginning of fitting....

 

[etpm]

The thing is one can prevent pieces of PTFE tape from coming lose and clogging system if you start the tape wrap leaving 1-2 thread bare at beginning of fitting....

You are correct. But you forgot to mention that the other thing is people often don't do that, leave the first one or two threads bare. Even though it is "common knowledge".
Eric

 

[lpakiz]

DL,
If you disassemble a teflon taped fitting, you need to be really careful to remove ALL the scraps of tape left in the female part before reassembling. Some of those scraps are really small and hidden in the female threads but get pushed out of the thread by the male being advanced into the fitting--the second time.

On a related subject:
Once I helped a friend in the maple syrup equipment manufacturing business set up for a trade show. I screwed a DRY 1/2" SS nipple into a DRY SS female device, HAND TIGHT (for demo purposes only) and it galled the threads so bad it ruined both pieces.