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.....

 

[Scooby074]

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.....

Gotta love it... Price goes up as their cost goes down

 

[Tractor Seabee]

Not sure what you all are doing based on some of the comments.

If you need pipe nipples or fittings on hydraulics, DO NOT USE PLUMBING FITTINGS. Even EX heavy nipples are only rated at 1000 PSI and standard plumbers fittings, black or galvanized are only rated for 150 PSI. Hydraulics are working at 1000-3000 PSI depending on your tractor. Minimum is forged steel fittings and Schd 80 seamless nipples. You get a better quality thread. Buy at your hydraulic supply house as they will have in stock. You are not going to find this stuff at the big box stores or auto supply stores. If you need many nipples and fittings you are better off to use hydraulic tubing and steel hydraulic flatre fittings. One good thing is if the cheap stuff does burst pieces will not fly around like stuff holding air, gases, or steam. But the hot oil sraying around can give some nasty burns.

Old pipefitter talking.

Ron

 

[Soundguy]

Buy at your hydraulic supply house as they will have in stock. You are not going to find this stuff at the big box stores or auto supply stores. Ron

napa carries a good selection of REAL hyd fittings.. they can order parker.. etc.. I believe napa qua;lifies as an auto supply store no?

soundguy

 

[wdchyd]

Not sure what you all are doing based on some of the comments.



Old pipefitter talking.

Ron

Ron, If you read my comments I used the black iron fittings on a FHW (forced hot water) boiler......at no time have I suggested anything other than "Real" hydraulic fittings for hyd systems........the hydraulic fittings that I referenced made in china are from Gates, Aeroquip and Parker.....

Old Hydraulic Technician Talking

Bill

 

[wdchyd]

napa carries a good selection of REAL hyd fittings.. they can order parker.. etc.. I believe napa qua;lifies as an auto supply store no?

soundguy

My local Napa uses Weatherhead (ie: Eaton/Aeroquip)......Yes, an auto supply store

 

[Errol]

Our intials stand for bspt british standard pipe taper bspf british standard pie fine meaning parallel the same with nptt national pipe thread taper and nptf national pipe thread fine meaning parallel and the pipe thread diameter is slightly smaller to allow for no taper so a parallel thread would be loose in a taper fitting and not be able to seal as you said parallel are usually in valve bodies

 

[Scooby074]

Not sure what you all are doing based on some of the comments.

If you need pipe nipples or fittings on hydraulics, DO NOT USE PLUMBING FITTINGS. Even EX heavy nipples are only rated at 1000 PSI and standard plumbers fittings, black or galvanized are only rated for 150 PSI. Hydraulics are working at 1000-3000 PSI depending on your tractor. Minimum is forged steel fittings and Schd 80 seamless nipples. You get a better quality thread. Buy at your hydraulic supply house as they will have in stock. You are not going to find this stuff at the big box stores or auto supply stores. If you need many nipples and fittings you are better off to use hydraulic tubing and steel hydraulic flatre fittings. One good thing is if the cheap stuff does burst pieces will not fly around like stuff holding air, gases, or steam. But the hot oil sraying around can give some nasty burns.

Old pipefitter talking.

Ron

sched 40 on suction side only. no galv. watch for loose flash

 

[Tractor Seabee]

Ron, If you read my comments I used the black iron fittings on a FHW (forced hot water) boiler......at no time have I suggested anything other than "Real" hydraulic fittings for hyd systems........the hydraulic fittings that I referenced made in china are from Gates, Aeroquip and Parker.....

Old Hydraulic Technician Talking

Bill

Sorry Bill, these threads sometimes wander around the subject so that it is hard to track unless you go back to the beginning which I did not do here. I had added a comment on this a long way back and did not follow that close. I was only pointing out the pitfalls of using some info not related to the base subject. Unfortunanetly due to a lack of knowledge folks get to thinking price and make these type mistakes. Back when I was plying the trade it was amazing what you found general handyman mechanics in small plants would do to keep things running. Then they called us to fix it when they got into trouble. I am with you on the china thing. It is a mixed bag. Seems some of the name brands do have a good handle on Quality Control overseas. I think that is probably the key, stay with known old time US brand names. For industrial hydraulic piping we almost always used Parker tube/hose fittings, forged steel fittings and seamless pipe and nipples. Some stuff had to be schd 160 even when getting up towards pressures higher than tractors are. We never used malleable fittings on hot water or steam boilers; either cast iron or steel depending on pressure. Hot water and LP steam heating hasen't used threaded pipe much since the 1960's. Either welded or copper tube.

Ron

 

[MHarryE]

From the OEM standpoint, leaks equal mechanic visits and warranty claims. Number 1 way to avoid hydraulic line leaks is to avoid pipe threads and instead use ORB (o-ring boss) ports and ORFS (o-ring face seal) connectors. If, however, you are forced to use pipe threads because nobody makes what you need with the preferred, always use a thread sealant. The 3 large OEMs for whom I worked all used the same thing for pipe threads - whichever Loctite hydraulic sealant was best at the time. At one time we had a rash of hydraulic motor shaft seal leaks from 1 plant (identical machine built at 3 plants worldwide and only the US built machines leaked). We had a bunch of the leaky motors returned - bits of teflon in the seals causing the leaks. Investigate the assembly line - someone had decided to change from sealant to Teflon tape on the sole pipe fitting used on the machine and the teflon tape chemically matched the bits found in the seal. Change from tape back to the specified sealant and problem resolved.

 

[crazyal]

From the OEM standpoint, leaks equal mechanic visits and warranty claims. Number 1 way to avoid hydraulic line leaks is to avoid pipe threads and instead use ORB (o-ring boss) ports and ORFS (o-ring face seal) connectors. If, however, you are forced to use pipe threads because nobody makes what you need with the preferred, always use a thread sealant. The 3 large OEMs for whom I worked all used the same thing for pipe threads - whichever Loctite hydraulic sealant was best at the time. At one time we had a rash of hydraulic motor shaft seal leaks from 1 plant (identical machine built at 3 plants worldwide and only the US built machines leaked). We had a bunch of the leaky motors returned - bits of teflon in the seals causing the leaks. Investigate the assembly line - someone had decided to change from sealant to Teflon tape on the sole pipe fitting used on the machine and the teflon tape chemically matched the bits found in the seal. Change from tape back to the specified sealant and problem resolved.

You would be surprised just how many times someone somewhere decides to make a change because they don't think it will make a difference. That's one of the biggest challenges to large companies.