Parallel or Series, which is better?

[diesel]

Sorry for not being clear.

Yes, I am talking about pnuematic tanks.
We have one piston on our robot.
Will putting the tanks in parallel provide more force?
Will putting them in series make the pressure last longer?
And any other facts would be great.

Thanks.

[MrForbes]

The air from the tanks all has to go through one regulator, so it really does not matter how you connect the tanks....things will be moving slowly if the cylinder is large diameter.

[Gary Dillard]

Originally Posted by diesel

Sorry for not being clear.

Yes, I am talking about pnuematic tanks.
We have one piston on our robot.
Will putting the tanks in parallel provide more force?
Will putting them in series make the pressure last longer?
And any other facts would be great.

Thanks.

1) Putting the tanks in parallel does not provide more force. Force in your piston is generated by the area of the piston times the pressure downstream of the regulator, which is the lesser of the regulator setting (60 psi default, lower if you dial it down or use a second regulator) or the pressure in the tanks (when the regulator no longer has to "regulate" a higher pressure down to its setting). The pressure is the same in both tanks (and all the tubing up to the regulator) regardless of whether it is a series or parallel connection because it is really just one big volume of air connected by tubing. Since you are drawing air out of this volume through the same size tubing, the remaining air is able to stabilize/equalize to the same pressure regardless of where you remove air from the storage volume.

2) By similar reasoning, the pressure will last the same amount of time for series and parallel, because you are storing the same volume of air either way, and removing the air at the same rate either way.

[David Brinza]

Speaking of parallel:

Is it legal to use two regulators in parallel to provide 60 psi to pistons from the 120 psi tanks? Twice the flow would be available...

[Mr. Freeman]

Originally Posted by David Brinza

Speaking of parallel:

Is it legal to use two regulators in parallel to provide 60 psi to pistons from the 120 psi tanks? Twice the flow would be available...

I thought about doing that on our robot, but I don't think it's legal.

<R98> “Working” air pressure on the ROBOT must be no greater than 60psi. All working air must
be provided through the Norgen adjustable pressure regulator, and all other pneumatic
components must be downstream from this regulator. A pressure gauge must be placed
adjacent to the pressure regulator and display the downstream pressure.

[Daniel_LaFleur]

Originally Posted by diesel

Sorry for not being clear.

Yes, I am talking about pnuematic tanks.
We have one piston on our robot.
Will putting the tanks in parallel provide more force?
Will putting them in series make the pressure last longer?
And any other facts would be great.

Thanks.

OK, the simple answer is ... it depends.

It depends on what is the controlling orifice (what has the most restriction or lowest CV) as to whether series or parallel is better. squirrels' answer assumes that the regulator is the controlling orifice, which is generally not true. Usually the valve has the controlling orifice.

Changing the path at the controlling orifice (IE splitting the flow path and having it run through 2 valves) will garner you the biggest bang for the buck.

Originally Posted by David Brinza

Speaking of parallel:

Is it legal to use two regulators in parallel to provide 60 psi to pistons from the 120 psi tanks? Twice the flow would be available...

I believe that the regulators are a 'bleed' type which means that when the output overpressurizes (goes over the setpoint pressure of the diaphram) the regulator bleeds off the excess pressure through a pressure relief vent. This would mean that if both regulators weren't set EXACTLY at the same pressure (no easy feat) then one would continue to supply air while the other would be venting it, and that would tax your on-board compressor.

[Gary Dillard]

Originally Posted by Daniel_LaFleur

OK, the simple answer is ... it depends.

It depends on what is the controlling orifice (what has the most restriction or lowest CV) as to whether series or parallel is better. squirrels' answer assumes that the regulator is the controlling orifice, which is generally not true. Usually the valve has the controlling orifice.

We're splitting hairs here, but in reference to his question - should the tanks be in series or in parallel, the fact that the valve is the controlling orifice has nothing to do with the answer to that question. By the rules, all the flow from the tanks has to go through a single tube into a single regulator and then out to the system. Regardless of whether you put one valve or 10 valves downstream, the rate at which air will go through that one tube and one regulator is not dependant on whether the tanks are in series or parallel. The storage volume will discharge at the same rate.

[Los Frijoles]

All that tanks really are is very large diameter tubing. Since Air is a gas, it will flow freely to fill up the entire space that it is given, so placement of the tanks does not have a serious effect on the way the air flows. Only in applications where the movement of air is critical and at high velocity like pneumatic potato guns does tank placement matter.

[Daniel_LaFleur]

Originally Posted by Gary Dillard

We're splitting hairs here, but in reference to his question - should the tanks be in series or in parallel, the fact that the valve is the controlling orifice has nothing to do with the answer to that question. By the rules, all the flow from the tanks has to go through a single tube into a single regulator and then out to the system. Regardless of whether you put one valve or 10 valves downstream, the rate at which air will go through that one tube and one regulator is not dependant on whether the tanks are in series or parallel. The storage volume will discharge at the same rate.

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.

[David Brinza]

Originally Posted by Daniel_LaFleur

I believe that the regulators are a 'bleed' type which means that when the output overpressurizes (goes over the setpoint pressure of the diaphram) the regulator bleeds off the excess pressure through a pressure relief vent. This would mean that if both regulators weren't set EXACTLY at the same pressure (no easy feat) then one would continue to supply air while the other would be venting it, and that would tax your on-board compressor.

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.

[dlavery]

Originally Posted by David Brinza

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.

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

-dave



.

[David Brinza]

Originally Posted by dlavery

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

-dave



.

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

[Gary Dillard]

Originally Posted by diesel

Sorry for not being clear.

Yes, I am talking about pnuematic tanks.
We have one piston on our robot.
Will putting the tanks in parallel provide more force?
Will putting them in series make the pressure last longer? And any other facts would be great.

Thanks.

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.

[dtengineering]

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

[Daniel_LaFleur]

Originally Posted by dtengineering

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

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