pipe thread?

[kenmac]

Pipe compound, etc, is only a lubrciate for the threads. Threads actually make the seal to keep a joint from leaking

 

[J_J]

You now have to ask yourselves. Is NPT and NPTF used interchangeably?

If the answer is yes, then should one use a lubricant/sealer?

Excerpts:

A number of variations of the NPT thread has been introduced to overcome the problem of spiral leakage and they are generally known as Dryseal threads. (Covered by the SAE standard J476). The best known is the NPTF (the F standing for fuel). In this thread design, the root diameter has been increased so that when the internal and external threads are screwed together, there is an interference fit between the crest of one thread and the root of the other so as to seal against spiral leakage.

Many quick disconnect couplers for example have the NPSF thread and are recommended by the manufacturer for use with NPT (!) and NPTF.

Excerpts:

Contact at the crest and root prevents spiral leakage and insures pressure-tight joints without the use of a lubricant or sealer.

However,

Lubricants, if not functionally objectionable, may be used to minimize the possibility of galling in assembly.

So, is there any one person that knows it all for sure? Surely not me. One can only do what one thinks is right.

A certificate or license that says one is smarter than another, I doubt that.

 

[Tractor Seabee]

Teflon tape is bad news on any pipe thread unless you are very careful to leave the first two threads bare so nothing gets carried inside the system. As said before it can ruin a pump or clog small orfices if no filter is ahead of that item. There are many liquid and paste lube/sealants on the market; make sure what you use is not disolved by petroleum products and does not get hard over time. Permatex is one I use often. If pipe threads were a precision machined/polished connection you would only need a lubricant; but the nature of the beast is you need to seal around the minor imperfections. W/o lubricant in the joint compound you would make the imperfections worse. Any thing you use, keep it off the first threads and the end of the fitting. After removing a fitting use a small tool like a dental pick to remove any loose pieces of sealant left as when the new fitting is installed it will push that stuff right into the system. Loc-Tite makes some good stuff also.

Ron

 

[Errol]

In Australia nptf is a parallel thread and should use a dowty seal which is a metal ring with a rubber seal built in to the inside and no matter what type of sealant you use if you use to much it still hardens and travels around your system if you use a sealant which I always have working on industrial hydraulic systems for 30 years and never had any problems or leaks just make sure everything is clean before applying the sealant of your choice and do not use excessive amounts and all hose swivel hose fittings do not use any sealant as they have tapered seats to do the job and i have never heard of a dry fitting joint as all threads have clearance and will leak no mater how tight

 

[Discount Hydraulic Hose]

In Australia nptf is a parallel thread and should use a dowty seal which is a metal ring with a rubber seal built in to the inside...

I think you're referring to British Standard Pipe (B.S.P.), which is available with tapered (B.S.P.T.) or parallel (B.S.P.P.) threads. The Parallel version uses a washer and O-ring or a bonded seal when it's mated with a port or solid female fitting.

Metric fittings, also parallel thread, commonly use the same sealing method.

N.P.T.F. stands for National Pipe Taper Fuel. It would be highly confusing to use that designation for a parallel thread.

 

[5030]

Some of your information is good and some not so good. The OP asked a simple question about sealing so why mention a fitting (NPTF Dryseal) that there is a 99.99% chance he doesn't have? Or mention it for his knowledge and move on to what he probably has and include your thoughts on sealing.

NPT threads are not expected to seal dry and need a sealant.[/QUOTE]

Not always. Depends entirely on the joining materials. In maleable that's true. In say Delrin, it's not.

 

[5030]

I think you're referring to British Standard Pipe (B.S.P.), which is available with tapered (B.S.P.T.) or parallel (B.S.P.P.) threads. The Parallel version uses a washer and O-ring or a bonded seal when it's mated with a port or solid female fitting.

Metric fittings, also parallel thread, commonly use the same sealing method.

N.P.T.F. stands for National Pipe Taper Fuel. It would be highly confusing to use that designation for a parallel thread.

Ken...

I bought a couple dozen WOG valves from you a couple months ago. Good valves and a great price plus fast delivery.

 

[wdchyd]

Loctite 592 PST.

Tape SHOULDNT be used, especially on any of the pressure or supply lines...

HOWEVER, lately ive been seeing major issues with chinese sched 40 pipe and fittings being basically crap, and leaking like a sieve no matter what dope was used or tightness achieved.

A trick i learned from an old timer was to smear dope on the threads first, then a wrap or 2 of tape 2-4 threads back from the opening (so you dont contaminate the fluid), then cover that with a layer of dope. You WONT have any leaks after this, even on poorly made fittings. But you muat take extreme care to keep the tape well back from the opening, especially on supply lines to the pump.

Another oldtimers trick was to wrap the threads of the pipe in silk thread along with dope. I havent done the latter, but have had great luck with the above trick on problematic fittings.

I like and use the Loctite PST also.....

a few years ago I replaced my FHW boiler and had troubles getting chinsy black-iron fittings to seal (from Cheapo Depot).....ended up doing exactly that trick with putting dope on threads first, then couple wraps with teflon tape.....it worked...

I wouldn't do it on hyds though......Loctite PST is for that

 

[Scooby074]

I like and use the Loctite PST also.....

a few years ago I replaced my FHW boiler and had troubles getting chinsy black-iron fittings to seal (from Cheapo Depot).....ended up doing exactly that trick with putting dope on threads first, then couple wraps with teflon tape.....it worked...

I wouldn't do it on hyds though......Loctite PST is for that

Good trick isnt it:thumbsup:

I learned it from an old mechanic i apprenticed under. Its a last ditch on hydraulics (due to the risk of contamination) but it can be used if very careful (and stingy) with the tape.

Maybe some others will use this trick someday... particularly with the crappy fittings from china. I dont think you can even get NA made fittings anymore. Even the supply houses have chinese junk now.

Something else, even genuine hydraulic fittings are out of china now. Just bought a bunch of Gates and Aeroquip fittings NPT and JIC ... All china. But at least the quality of the threads is decent (no leaks), but i hate paying NA prices for items made in china.

 

[wdchyd]

It's a good trick Scooby, I learned it from a union-pipefitter friend......

The only thing was you had to tighten, wait 5 minutes, tighten, wait, tighten, wait......for each connection.....it was a PIA but it gave a leakproof connection for junky/new BI pipe elbows and fittings....the teflon/paste would slowly ooze out and loosen the fitting if you didn't stay with it

Also agree with you regarding the hyd adapters made in asia......I sell Gates and they didn't go down in price when the "Made in China" stuff showed up....IIRC I had two price increases this past year.....