[AT] pipe threads

[Ken Knierim]

Excellent post, Steve. Very good information I can use!

Thanks!

Ken in AZ

On 6/25/06, Steve W. <falcon at telenet.net> wrote:
> NPT   American Standard Pipe Taper Thread
>
> NPSC   American Standard Straight Coupling Pipe Thread
>
> NPTR   American Standard Taper Railing Pipe Thread
>
> NPSM   American Standard Straight Mechanical Pipe Thread
>
> NPSL   American Standard Straight Locknut Pipe Thread
>
> NPTF   American Standard Pipe Thread Tapered (Dryseal)
>
> BSPP   British Standard Pipe Thread Parallel
>
> BSPT   British Standard Pipe Thread Tapered
>
> The best known and most widely used connection where the pipe thread
> provides both the mechanical joint and the hydraulic seal is the
> American National Pipe Tapered Thread, or NPT. NPT has a tapered male
> and female thread which seals with Teflon tape or jointing compound.
> Pipe threads used in hydraulic circuits can be divided into two types:
> a) Jointing threads - are pipe threads for joints made pressure tight by
> sealing on
> the threads and are taper external and parallel or taper internal
> threads. The
> sealing effect is improved by using a jointing compound.
> b) Fastening threads - are pipe threads where pressure tight joints are
> not made on
> the threads. Both threads are parallel and sealing is affected by
> compression of a
> soft material onto the external thread, or a flat gasket.
>
> Plastic injection molded thread forms are manufactured to ANSI B2.1 and
> SAE J476 standards.
> The word "tapered" in several of the above names points to the big
> difference between many pipe threads and
> those on bolts and screws. Many pipe threads must make not only a
> mechanical joint but also a leakproof
> hydraulic seal. This is accomplished by the tapered thread form of the
> male matching the thread form of the
> female tapered thread and the use of pipe sealant to fill any voids
> between the two threads which could cause a
> spiral leak. The bottoms of the threads aren't on a cylinder, but a
> cone; they taper. The taper is 1?16 inch in an
> inch, which is the same as 3/4 inch in a foot.
> Because of the taper, a pipe thread can only screw into a fitting a
> certain distance before it jams. The standard
> specifies this distance as the length of hand tight engagement, the
> distance the pipe thread can be screwed in by
> hand. It also specifies another distance - the effective thread, this is
> the length of the thread which makes the seal
> on a conventional machined pipe thread. For workers, instead of these
> distances, it is more convenient to know
> how many turns to make by hand and how many with a wrench. A simple rule
> of thumb for installing tapered
> pipe threads, both metal and plastic, is finger tight plus one to two
> turns with a wrench. Torque installation values
> can be determined per application, but due to the variations involved in
> pipe joints such as dissimilar materials of
> male and female threads, type of sealants used, and internal variations
> in product wall thickness, a standard torque
> specification cannot be generically applied .
>
> A number of variations of the NPT thread have been introduced to
> overcome the problem of spiral leakage and are known as Dryseal threads
> (See SAE standard J476). The best known is the NPTF (F for Fuel). With
> this thread design, there are controls on the crests and roots of both
> the
> male and the female threads to ensure the crest crushes or displaces
> material into the root of the mating thread. The interference fit
> between the
> crest of one thread and the root of the other, along with the thread
> flanks matching, seals against spiral leakage.
> A variation of the Dryseal thread is the NPSF (National Pipe Straight
> Fuel). It is used for internal threads and a NPTF external thread can
> be screwed into it to provide a satisfactory mechanical connection and a
> hydraulic seal. The combination of a parallel and tapered thread is
> not regarded as ideal but is widely used. High quality plastic quick
> disconnect couplings typically use NPT threads.
>
>
> Steve Williams
> Near Cooperstown, New York
>
>
> ----- Original Message -----
> From: "David Myers" <walking_tractor at yahoo.com>
> To: "Antique tractor email discussion group"
> <at at lists.antique-tractor.com>
> Sent: Sunday, June 25, 2006 7:04 AM
> Subject: RE: [AT] pipe threads
>
>
> > Mike, that is my thinking on the letter designation
> > also (just a kinda made sense thing to me).  And to
> > add to my confusion is 'MTP' and 'FTP', I assume
> > meaning male and female taper pipe? (I have seen these
> > but are not sure if they're even a proper
> > designation).
> > JIC is a straight thread 37deg. taper SEAT fitting,
> > used for medium presssure hydraulics.  JIC is being
> > phased out in favor of the flat face O'ring fittings
> > (FFOR, For-Seal, and other trade names).  There is
> > also straight thread O'ring fittings, more commonly
> > used to mate to valve blocks etc.  Of course, I have
> > come across the dreaded 'Proprietary Fitting' WAY to
> > many times!  Hope this isn't the case.
> >
> > Dave Myers
> > Paw Paw, MI
> >
> >
> > --- Mike Reggie <mrreg_99 at hotmail.com> wrote:
> >
> > >
> > >   This is just a guess, but I always thought the "F"
> > > after the NPT stood for
> > > female, I've also seen it following the designation
> > > NPS, which is generally
> > > just used for electrical fittings and is the same
> > > thread without the sealing
> > > capability of the tapered thread. Again just a
> > > guess, but could the thread
> > > you are looking for be a JIC thread?? I don't know
> > > how long that thread has
> > > been in use, but it seems to be a finer thread than
> > > the standard pipe
> > > thread, and I think it tapers.
> >
> >
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