Need help with some Pneumatic Terminology

[Gary Dillard]

Originally Posted by Al Skierkiewicz

Matthew,
NPT=National Pipe Thread.

Actually Al, I always thought that was what it stood for. But just now I was looking up some pipe thread dimensions for a job at work (yes some of us actually have a real job this time of year) and found in Mark's Handbook that the T stands for Taper. NPS would be National Pipe Straight.

[Nate Laverdure]

Originally Posted by Gary Dillard

NPS would be National Pipe Straight.

Nominal Pipe Size

[Gary Dillard]

Originally Posted by Nate Laverdure

Nominal Pipe Size

No, actually in this context it is National Pipe Straight as I said.

From ANSI B1.20.1 "Pipe Threads, General Purpose", Section 1.2 Thread Designations:

1.2.2 Each of these letters in the symbols has a definite significance as follows:
N = National (American) Standard
P = Pipe
T = Taper
c = coupling
S = Straight
M = Mechanical
L = Locknut
H = Hose Coupling
R = Railing Fittings

Not to be confused with nominal pipe size (NPS); pneumatics generally uses tubing, which is specified by OD, not NPS.

[Nate Laverdure]

Originally Posted by Gary Dillard

No, actually in this context it is National Pipe Straight as I said.
...

Ah, I see, thanks.

[Al Skierkiewicz]

Thanks Gary,
It would seem that some vendors are still using old definitions.

[FrankJ]

The problem with TLAs (three letter acronyms) is that they mean different things to different people (Or the same people at different times.)
Pipe terminology is particularly bad because of historical precedent from different regions.

NPS to a lot of people & some standards is nominal pipe size. If you told them you wanted straight pipe thread, they would just look at you funny. (If you doubt that go to your local hardware store an ask them, if you live in the USA)

Cv is the conductance of flow. (inverse of resistance.) It is a handy way of knowing how much a particular valve or fitting flows. The easiest example is with liquid. A valve with a Cv of 1 will flow 1 Gal/Min with a pressure drop of 1 PSI. Note the unit dependance. Cv with pneumatics is more difficult because the flow is referenced to standard conditions. (Cubic feet per min at 14.47 PSI at 32 F, or 60F or 68F or 70F). Lets not get started with metric definitions. Anyway Cvs determined with consistent standards with let you know the relative size without worrying about all the illogic & math behind it. Which is what standards are all about.

General tips.
Go to the rules. Make sure your pneumatics is laid out in the correct way & that you understand well enough to explain it to your inspector.

Use Teflon tape on tapered fittings. Make sure the tape ends before the threads do so that you do not get bits of tape in the system or block the end of the fitting. Do not over torque the fittings.

Do not use teflon tape on straight thread fittings. It will not do anything useful.

Make sure you tubing is cut square. It seals better in the push fittings that way.