Plumbing parts: tapered or not?

[puks]

I was told the NA standard is tapered threads and local plumbing stores sell such parts.

BRS parts are not tapered. When using such parts it's easier to predict a final size when everything is connected.

Does it matter which parts to use?

 

[lingwendil]

No, it doesn't, so long as they don't leak

Use some teflon tape on threads (sparingly and don't over tighten.

 

[laverda]

Threaded PVC should not use teflon tape as your more likly tp split the fittings and not get a leak proof joint. Teflon past is the proper sealer for threaded PVC joints per the manufacturers.

 

[fishyguy7]

Exactly what Laverda said

 

[oreo57]

I was told the NA standard is tapered threads and local plumbing stores sell such parts.

BRS parts are not tapered. When using such parts it's easier to predict a final size when everything is connected.

Does it matter which parts to use?

Sorry that is a bit confusing to me..
Tapered threads are used internationally.. well UK and the US for sure.
NPT BSPT
Boring article on thread type and ID:
https://trimantec.com/thread-identification-guide/

The purpose was to get a metal to metal seal.
Technically no "sealant" was needed.
Sloppy manuf of threads and assembly have created the need for a bit more.
Also helps in dis-assembly..

Straight threads are usually accompanied by an o ring or some sort of gasket.
Sealing straight threads w/ tape/dope is not recommended.

https://www.homedepot.com/p/RectorSeal-T-Plus-2-in-4-oz-Teflon-Pipe-Thread-Sealant-23631/100201204



"Teflon" tape was developed as a lubricant and aid in disassembly. Not a sealant.. though I guess in a sense it has exceeded its expectations..
https://www.plantengineering.com/articles/guidelines-for-choosing-a-pipe-thread-sealant/

 

[laverda]

Electrical fittings have straight threads and as stated above use an o-ring. The threads have the same pitch and nominal so they will screw together.

 

[puks]

Well, after several calls to BRS I realized they don't know for sure if the threads are tapered or straight (unless it's directly mentioned in the description on the site).

From Understanding NPT, NPTF & NPS Thread Connections
NPS = National Pipe Straight
NPT = National Pipe Thread
NPTF = Nation Pipe Thread Fuel

Both NPT and NPS have the same thread angle, shape, and pitch (threads per inch). However, NPT threads are tapered and NPS threads are straight (parallel). Both threads have a 60° included angle and have flat peaks and valleys. Tapered Pipe Thread is commonly found on ends of pipe, nipples and fittings (ex: couplings, elbows, tees, etc.).

Sharply angled threads are very critical to joint being tight with no leaks. Thread sealant or tape is typically required to complete the seal. Straight Pipe Threads need a gasket or O-ring to create a seal. While NPT and NPS threads will engage, they do not seal properly with each other.

 

[oreo57]

Well, after several calls to BRS I realized they don't know for sure if the threads are tapered or straight (unless it's directly mentioned in the description on the site).

From Understanding NPT, NPTF & NPS Thread Connections
NPS = National Pipe Straight
NPT = National Pipe Thread
NPTF = Nation Pipe Thread Fuel

Both NPT and NPS have the same thread angle, shape, and pitch (threads per inch). However, NPT threads are tapered and NPS threads are straight (parallel). Both threads have a 60° included angle and have flat peaks and valleys. Tapered Pipe Thread is commonly found on ends of pipe, nipples and fittings (ex: couplings, elbows, tees, etc.).

Sharply angled threads are very critical to joint being tight with no leaks. Thread sealant or tape is typically required to complete the seal. Straight Pipe Threads need a gasket or O-ring to create a seal. While NPT and NPS threads will engage, they do not seal properly with each other.

NPT National pipe taper American National Standard Taper Pipe Thread Tapered for sealing, often without any thread sealant; for connections in nearly every type of service

https://en.wikipedia.org/wiki/National_pipe_thread

If you ever disassembled the CGA side of gas regulators you will find most use nothing to seal the NPT threads..Metal to metal.
That said, it is sort of arguable both ways.
I use pipe dope on all NPT threads.. mostly because of cheap Chinese cutting and being an amateur..

Dig into the taper pipe thread lore and you will find all sorts of information and misinformation. If you want sealing without dope you are supposed to use NPTF. The F is for fuel, and also known as dryseal.

you usually can see the taper..

anyways measure the diameter on the front and the back of the threaded part..


It's complicated though..
https://www.cpcworldwide.com/Downloads/NPT.pdf

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

https://finishlinefactory.com/technical-info/npt-technical-information/

 

[puks]

It's complicated though..
https://www.cpcworldwide.com/Downloads/NPT.pdf

It's a great doc. Thanks oreo57