how do I get my NPT connections to not leak

[Mace Canute]

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).

This! Some people seem to think the contamination happens when it's assembled with the tape being wrapped over the end of the male fitting but it's far more likely to happen when a bit of tape gets left behind in the female portion of the fitting when it's disassembled and then pushed in when the male fitting is reassembled.

There's some good information about tightening pipe threads in this site:

Pipe Thread Installation Torque Table Chart | Engineers Edge | www.engineersedge.com

 

[ericm979]

The Loctite 242 worked on the last leaky connection. Thanks!

Also thanks for the torque table. The torque values sound really low though.

 

[Tractor Seabee]

Note in that torque table there are two threads left showing. That is the point when the two tapered surfaces are at the optimum point. That means that both the male and female threads are made proper length/depth. That's why threading with a die you go two threads past

Ron

 

[Texasmark]

I thought this was Teflon Tape was for or am I on the wrong page again.

Teflon tape is NOT recommended for hydraulic fittings as if improperly applied, it can circulate through the system and may wind up in a valve preventing it from closing properly.

Liquids and pastes are recommended. I have found high pressure pipe dopes online. I use a plumbers all purpose semi-liquid that's grey and is applied with a brush, local hardware store carries it that does the job for me.

I think Permatex #2 (remains flexible) would be an alternative; #1 (becomes rigid) if I knew I'd never want to open the joint....available at auto parts stores should work too as was indicated by Tom. I also have an Aviation adhesive/gasket sealer that a local AP store carries that would work real well.

On how tight, I can only get them so tight with 2 suitable wrenches and my strength. That's how tight I get mine.

 

[dougtrr2]

When I was in the service I went on many dispatched for leaking diesel fuel systems, primarily in the day tank and transfer pump area. Only once did a part actually need to be replaced. All the rest of the time I just took it apart, cleaned off all the miswrapped Teflon tape, put on a new layer and put in back together. One time I had to replace a fitting. I did my trick of putting on the Teflon properly, but the more I tightened it the worse it leaked. Then a close inspection of the back side of the fitting revealed a crack from over tightening. The more you tightened the wider the crack.


Doug in SW IA

 

[LD1]

Lots of opinions so I'll give mine.

Throw the tape away.

Use loctite 545. It's what it's made for.

How many threads do we see about valve or coupler issues.

Just one now about a possible load check sticking j. A yanmar.

People complain about leaky couplers when unhooked.

Not saying that Teflon is the cause.......but if you get shards of tape in the system.....those problems are exactly what happens.

 

[downsizingnow48]

Never seen a thread that says "I used loctite 545 and it leaked". !!!

 

[Ford850]

LOCTITE 545
(Known as Loctite 545 Thread Sealant Hydraulic/Pneumatic Sealant )
High lubricity thread sealant for locking and sealing metal pipes and small fittings with fine threads.
LOCTITE® 545 is a pipe thread sealant designed for locking and sealing of metal pipes and fittings. It is specially formulated to offer high lubricity for easy assembly and removal. Recommended for fine threaded fittings as used in hydraulic and pneumatic installations and small fittings in general. Suitable for fittings up to 50 mm in diameter including pneumatic and hydraulic fittings.
Your benefits:
Excellent solvent resistance
ABSSM approved
CFIA approved
Contains no fillers or particles that could contaminate system fluids, foul valves, or clog fine filters and screens

 

[downsizingnow48]

TBN has so many threads on valve related problems. Have to wonder how many caused by those nearly invisible teflon filaments.

 

[PILOON]

I have observed that many offshore pneumatic and hydraulic devices seem to use an epoxy of some sort.
Guess once cured no leakage can occur but disassembly is almost impossible. (heat does help)

My 'go to' that has worked for me is a urethane caulking* product generally used in construction to seal widows etc.
It very much resembles automotive windshield adhesive in most characteristics.
While it makes a great seal It also can be wrenched free.

*The brand that I know (may be regional) is Flextra.

 

[Mace Canute]

This! Some people seem to think the contamination happens when it's assembled with the tape being wrapped over the end of the male fitting but it's far more likely to happen when a bit of tape gets left behind in the female portion of the fitting when it's disassembled and then pushed in when the male fitting is reassembled.

There's some good information about tightening pipe threads in this site:

Pipe Thread Installation Torque Table Chart | Engineers Edge | www.engineersedge.com

Please ignore the information in the link I provided. It's bogus!

 

[Oldpath05]

LOCTITE 545
(Known as Loctite 545 Thread Sealant Hydraulic/Pneumatic Sealant )
High lubricity thread sealant for locking and sealing metal pipes and small fittings with fine threads.
LOCTITEｮ 545 is a pipe thread sealant designed for locking and sealing of metal pipes and fittings. It is specially formulated to offer high lubricity for easy assembly and removal. Recommended for fine threaded fittings as used in hydraulic and pneumatic installations and small fittings in general. Suitable for fittings up to 50 mm in diameter including pneumatic and hydraulic fittings.
Your benefits:
Excellent solvent resistance
ABSSM approved
CFIA approved
Contains no fillers or particles that could contaminate system fluids, foul valves, or clog fine filters and screens

("easy assembly and removal")<<<That's important, but ouch for the price this stuff better work and what about self life, does it go bad in 5 years, Teflon tape can stay on the shelf for 50 years>>> Loctite 54531 545 Pneumatic/Hydraulic Sealant, Size 5 Ml: Amazon.com: Industrial & Scientific

 

[ray66v]

A friend who is a retired pipe fitter, gave me go-no-go thread gauges to test my fittings before use.

As he predicted, they almost always are very marginal, and quite often fail.

The problem is, it's pretty much all junk out there anymore.

 

[downsizingnow48]

I don't know if it goes bad, I buy it in a tiny little bottle and use it up.

 

[CincyFlyer]

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

All well and good, unless you happen to need a hose or fitting on a Sunday.

 

[downsizingnow48]

As far as I know, all quick disconnects are female NPT. That is my only use for NPT in hydraulics.

 

[LD1]

Sometimes just no other choice. Valves, cylinders, QD's, etc as others have mentioned.

Hoses and fittings....no brainier. Design around npsm or jic.

Sometimes valves and.cylinders can be had with sae ORB ports. But not always. Especially if you are a bargain shopper like me.

I wish the industry as a whole would move away from npt. That's about the only way things will change

 

[ericm979]

I bought some of the Loctite 545. I've had bottles of other grades of Loctite for 10 years or more and they still work. Performance may have fallen some but I didn't notice it.

 

[bob 59912]

Parker 1/2" body ISO 5675 Quick Disconnects of the 4200 series come in 3/4"-16 ORB for both the nipples and couplers. The connect under pressure 8200 couplers and the 8010 nipples also come in both 3/4"-16 and 7/8"-14 ORB

 

[Deere Dude]

have a couple bottles of 242 sitting in the toolbox with caps not sealed just sitting on top of container. It has been 14 years already. A little bit goes a log ways.
I do have half a dozen rolls of tape and a bottle of Teflon paste there also. But for the sure to not leak joint I use 242, but will use any of the above except tape in hydraulics.