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.