Connecting 1/2" NPTF

Oldtoad · Feb 28, 2022

Got some hydraulic hoses in the mail with fittings.
Is there goo needed? Just crank 'em down?
Teflon tape can get into the system so care has to be taken with that.

Roadworthy · Feb 28, 2022

NPT is generally tapered to ensure leak prevention. A small amount of thread tape will smooth the tightening of the fittings. Of course you could use "goo" to help by lubricating and sealing the threads.

lpakiz · Feb 28, 2022

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.

Farmer495 · Feb 28, 2022

I've used tape...but VERY careful with it making sure it is uniform and a thread or two from the end of the fitting is exposed to prevent tape from coming off into the line.

the old grind · Feb 28, 2022

'Dopes/tapes' are lubes to allow tightening tapered threads to an interference fit. They are not meant to be stand-alone sealants.

My choice for NPT hydro lines is Permatex #2 non-hardening. It is fuel-proof & approved for high temps and steam fittings. Anything that leaks/weeps wasn't tightened enough.

Root Cause · Feb 28, 2022

+1 on dope

lpakiz · Feb 28, 2022

To add a bit more to my "no tape" policy, most times, with careful application of tape, the first assembly is just fine.
It is the subsequent disassembly and reassembly that pushes used tape ahead of the male part and into the oil-stream.

WranglerX · Feb 28, 2022

Use this on water, fuel, oils, and anything with tapered threads...

etpm · Mar 1, 2022

oldtoad said:
Got some hydraulic hoses in the mail with fittings.
Is there goo needed? Just crank 'em down?
Teflon tape can get into the system so care has to be taken with that.

NPTF is made to be used without any type of lube or sealant. It is also known as Dryseal. The thread has sharp crests that bite into the mating fitting which helps with the sealing. So thread goo isn't needed. If you later take it apart you may find that the thread is galled badly.
Eric

LouNY · Mar 1, 2022

And to really kick off the discussion teflon tape is not a sealant it is a thread lubricant.
A good thread lubricant will allow NPT threads to distort and seal with no damage,
so they can be broken apart and reassembled without leaks.

Username Taken · Mar 1, 2022

Oldtoad · Mar 1, 2022

LouNY said:
And to really kick off the discussion teflon tape is not a sealant it is a thread lubricant.
A good thread lubricant will allow NPT threads to distort and seal with no damage,
so they can be broken apart and reassembled without leaks.

How much do we put on the threads?
Put a call in to the vender, Discount Hydraulic Hose, they agreed.

LouNY · Mar 1, 2022

oldtoad said:
How much do we put on the threads?
Put a call in to the vender, Discount Hydraulic Hose, they agreed.

The old standard was 3 wraps

ericm979 · Mar 1, 2022

LocTite 545. My NPT hydraulic fittings leaked when I used teflon dope no matter how hard I tightened them. 545 and a day to cure and they are dry.

NPT is made for 60 psi water pipes, not 2500 psi hydraulics. It needs something like 545 to work.

dstig1 · Mar 1, 2022

ericm979 said:
LocTite 545. My NPT hydraulic fittings leaked when I used teflon dope no matter how hard I tightened them. 545 and a day to cure and they are dry.

NPT is made for 60 psi water pipes, not 2500 psi hydraulics. It needs something like 545 to work.

+1 on the 545 Loctite

MF RED in MT · Mar 1, 2022

+2 for Loctite 545

KC

LD1 · Mar 1, 2022

+3 loctite 545

jdmeth · Mar 4, 2022

Farmed for 25 years. I found out that, at least for me, only Teflon tape would seal NPT hydraulic hose fittings. Any thing else leaked.

ssmewing · Mar 4, 2022

etpm said:
NPTF is made to be used without any type of lube or sealant. It is also known as Dryseal. The thread has sharp crests that bite into the mating fitting which helps with the sealing. So thread goo isn't needed. If you later take it apart you may find that the thread is galled badly.
Eric

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.

ericm979 · Mar 4, 2022

NPT is tapered thread. The threads deform to form the seal. That's true for NPT water pipe and hydraulic fittings. You may be thinking of one of the 20 or so other hydraulic fitting types, most of which do not use the threads to form the seal. For example JIC. It uses conical mating surfaces to seal. No thread sealant needed. It is very common and is far superior to NPT. But they make a lot of fittings with NPT. I use it as little as possible and use adapters to get to JIC.

An excellent hydraulic fitting guide:

https://www.discounthydraulichose.com/v/vspfiles/downloadables/thread_guide.pdf

The first type of fitting they discuss is NPT, and they write:

"National Pipe Tapered Fuel (NPTF) This connection is still widely used in ﬂuid power systems, even though it is
not recommended by the National Fluid Power Association (NFPA) for use
in hydraulic applications. The thread is tapered and the seal takes place by deformation of the threads"