Re: Parallel or Series, which is better?
 

My answer is correct.

No valve in the KOP will flow gas faster than the tubes supplied, thus the tubes are not the controlling restrictor.

No valve will flow anywhere near the flow capacity of the regulator, thus again, the controlling restrictor is the valve.

Putting tanks in parallel will do nothing if the controlling restrictor is not the flow orifice from the tanks.

My explaination was to show how he could get higher flow and to point him in the proper direction as to why the flow through his pneumatic system is what it is.

His question was trying to flow gas faster, thus my suggestion to parallel the controlling restrictor, not the tanks or the regulators.

It's not splitting hairs ... it's the physics of gasses and I'm trying to get him to understand the answer, not give the answer to him.

Re: Parallel or Series, which is better?
 

I see 2 specific questions here. To which one is yours the correct answer?

His question was not about how to get air to flow faster. That was the question you answered, but that was not the question he asked. He has 2 tanks in his kit of parts and wants to know if it makes a difference how they are hooked up. Your information, although all very true and all very nice, didn't answer the question. And in fact, your answer "it depends", was wrong; whether to hook the tanks up in series or in parallel doesn't depend on anything. Hooking the tank up either in series or in parallel doesn't affect the force or make the pressure last longer. Period.

Re: Parallel or Series, which is better?
 

I think you're right about two regulators on a common 60 psi circuit.

I'm asking whether it's legal two have two independent 60 psi paths, each with its own regulator, valve and piston, operating off of a common 120 psi source.

Re: Parallel or Series, which is better?
 

Whatever the original question was about, this has resulted in a very good discussion of flow rates and bottlenecks in the pneumatics system to which I would like to contribute.

FIRST contends in the Q&A that the diameter of the tubing has been specifically chosen to restrict flow rates in the system, but Daniel's comments have encouraged me to look at some of the specs.

The FESTO valve, for instance, is rated at 14 "cfm"... I presume they mean scfm, which is about the same as the flow rate of the main system regulator. This means that if you are trying to fill a large cylinder quickly, putting two valves in parallel to that cylinder might speed things up a bit, but would mostly transfer the bottleneck right back to the main regulator. You're stuck with a 14 scfm bottleneck either way... which at 60psi works out to something like 100 cubic inches of compressed air per second.

Now let me add a generous quantity of "IMHOs" around here... my thermo and fluids marks at university weren't that great to begin with, and that was 20 years ago, but it seems to me that if the tubing is not the bottleneck that the way to fill a cylinder most quickly would be to put two or three of the clippard tanks downstream of the regulator (and thus only at 60 psi, but past one bottleneck) and use two or three valves in parallel to control the motion of the cylinder. This reduces the total amount of stored energy in the system, but may allow for higher flow rates, albeit for a briefer period of time.

If the tubing was the bottleneck (and my only evidence for that is the GDC's comments in the Q&A... which contradicts both my "gut feeling" and Daniel's assertions, but comes from a usually reliable source) then rather than using say, a 2"x8" cylinder, you could use two 1.5x8" cylinders to get similar force at a higher flow rate.

Or, as others have suggested, you could preload a cylinder by using a longer cylinder than needed, latching it in position, pressurizing it, and then allowing the gas to expand completely free of bottlenecks.

And if you're thinking of doing that, you probably want to make sure you read team update #5 about trackball launcher safety!

Jason

Re: Parallel or Series, which is better?
 

For the answer to that question, you may want to look at this Q&A answer.

-dave



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Re: Parallel or Series, which is better?
 

I couldn't ask for a more clearly stated answer to my question. Obviously, I should have consulted the official source FIRST!:o

Re: Parallel or Series, which is better?
 

Thank you for pointing me to the spec sheets. I was quite shocked to see the Norgren regulator only has a max flow rate of 14 SCFM, thats very low for a regulator. I guess that teaches me to look for the specs before making assumptions.

We ran tests running 2 festo valves in parallel with the 4 clippard volumes behind the regulator and it actually slowed down our cylinder. This makes sense with the regulator and Valve being series orifices and the "T"s creating non-laminar flow. We then changed back to 1 Festo valve and moved 2 of the clippard volumes to downstream of the regulator and this greatly increased our cylinder speed.

Again, thanks Jason. I hate it when I'm being a dolt :p