Legal Pneumatic Fittings - Nipples & Elbows?
 

R77 of the 2014 game manual states "Pressure transducers, pressure gauges, flow control valves, and connecting fittings" are legal. Can I assume that means any connecting fittings (which are rated for the pressure)?

We're looking to use 1/4" nipples and elbows to connect a tank to a nearby (stationary) cylinder, rather than 0.16" ID tubing for better flow rate. It looks legal to me, (especially as many teams use manifolds and cylinders with 1/4" npt ports).

Re: Legal Pneumatic Fittings - Nipples & Elbows?
 

Also according to R77 (e), any tubing used has to have an ID of 0.16". So I don't think using 1/4" NPT would be any more useful since you're still limited by the tubing.

Are you sure it isn't ports with 1/4" OD that you're thinking of? Because the 1/8" NPT ports we have fit 1/4" OD tubing. The 1/8" NPT ports have an ID of 1/8". It can be a bit confusing that the 1/8" NPT ports have labels on them saying 1/4.

Re: Legal Pneumatic Fittings - Nipples & Elbows?
 

We've done it in the past with no issue. You can always set it up with the fittings you want and fix it if it is not legal provided it is something you design to be easily changeable

Re: Legal Pneumatic Fittings - Nipples & Elbows?
 

That's just it. Elbows and nipples are *not* tubing, so I am thinking that rule doesn't apply. We are planning to use 1/4" (nominal ID) pipe nipple to go into a 1/4" NPT port.

Re: Legal Pneumatic Fittings - Nipples & Elbows?
 

I see. I would be careful though, perhaps someone should ask about this on the q&a.

Re: Legal Pneumatic Fittings - Nipples & Elbows?
 

Guys,
Can we agree that "we used it in the past" is not a response.
Thanks.

Re: Legal Pneumatic Fittings - Nipples & Elbows?
 

There are very few restrictions on the use of "fittings", just be careful in defining a fitting. For example;

A quick exhaust valve is not a fitting, Nor is a check valve, but a 1/4" NPT close nipple is.

Also keep in mind that the 1/8" NPT restriction is for valves, not fittings. It is allowable to use fittings larger than 1/8" NPT, just not valves that have ports larger than 1/8" NPT.

Re: Legal Pneumatic Fittings - Nipples & Elbows?
 

The question is do you consider a nipple a fitting or a tube. I would tend to consider a close (short) nipple a fitting (legal). At some point it would transition into a pipe, which it really is, which be closer to tubing (not legal)

Keep in mind I am not the one inspecting your robot.

Re: Legal Pneumatic Fittings - Nipples & Elbows?
 

Thanks for the input. I'm glad to get some backing on my interpretation.

Personally I'm not worried about a "pipe" being mistaken for "tubing". In this area, "tubing" usually means flexible (or at least, bendable). I'm guessing the rule is there to minimize damage if the vulnerable plastic tubing is cut or disengaged, which isn't a risk with hard pipe. I agree the question is probably worth a Q&A (I don't know how to do that though - I'm a first year mentor).

Re: Legal Pneumatic Fittings - Nipples & Elbows?
 

In that case "pipe" is not a fitting & not on the list of approved items. You probably OK with short nipples, without a Q&A only your inspector knows for sure.

Re: Legal Pneumatic Fittings - Nipples & Elbows?
 

The rule was simplified this year as 0.160 ID tubing has the same flow restrictions as saying Cv of 0.32 or about the same flow as 1/8" NPT port diameter.

Re: Legal Pneumatic Fittings - Nipples & Elbows?
 

If 1/8" NPT port diameter has a Cv of 0.32, then why would a solenoid with 1/8" NPT output advertise a Cv of 0.75? (mcmaster 6124K511)

Re: Legal Pneumatic Fittings - Nipples & Elbows?
 

The CV of a valve is a calculated number that includes the fitting size and the internal restriction of the valve and is basically just used for valves.

I think what Al was saying that using port size and hose ID is just a way of restricting flow like quoting a CV value.

Using CV can be pretty confusing because some valves give flow rate and some give CV which is not the same number. Eliminating the CV restriction and just using port size and hose ID is much easier to understand and inspect.

Re: Legal Pneumatic Fittings - Nipples & Elbows?
 

(emphasis mine)

right, so if a solenoid has a 1/8 NPT port, and the Cv of the 1/8 NPT is 0.32, then how can the Cv of the solenoid which includes said port and internal restriction be 0.75?

Re: Legal Pneumatic Fittings - Nipples & Elbows?
 

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.

Any way no matter how free flowing a valve is, the restrictions in the 1/4 OD tube restrict the flow to something acceptable to the GDC. I think that was what Al was saying. You would have to know the length of tube to calculate the exact Cv for it.