Parallel Tanks

[AdamC]

Is there a way to hook up your air tanks in parallel, as opposed to series? I understand that the benefits of wiring circuits in parallel, but I doubt it applies to air systems. I would think that the moment a failure occurs in a line that is not cut off by a solenoid, the system would immediately decompress. Any elaboration on this would be very welcome.

[Richard Wallace]

The 2007 FRC Pneumatics Manual shows a typical air circuit diagram on p. 11 and photograph on p. 12.

Since all air upstream of the Norgren regulator is at the same pressure, I'm not sure what you mean by "series" and "parallel" tank connection.

[Daniel_LaFleur]

Originally Posted by AdamC

Is there a way to hook up your air tanks in parallel, as opposed to series? I understand that the benefits of wiring circuits in parallel, but I doubt it applies to air systems. I would think that the moment a failure occurs in a line that is not cut off by a solenoid, the system would immediately decompress. Any elaboration on this would be very welcome.

Because gas expands to fill the area, any leak will cause a (nearly) uniform drop in the entire system, barring restrictions within the system. Thus you are correct that any failure in the integrity of the system would depressurize the entire system.

The only advantage to a parallel tank setup could be in flow rate as there is a larger effective orifice (2 tubes rather than 1). But that would require a double setup all the way through the (2) regulators (which may be against FIRST robot rules).

[tseres]

ya, unless you want to use larger tube throughout your entire air system, series is fine. as stated above, if there is any leak, the entire system is done for. with series tanks, all the pressure flows through the same 1/4" tubing. With parallel, you would have the same pressure, but twice the volume flowing through the same narrow tubing.

i'm probably wrong, but my point is that you shouldn't worry about it. with our robot, we just connected the tanks up before the pressure regulator. one tank just flowed into another. it worked fine. forget the series and parellel. just connect them in whatever order you want...the point is that it's still going to hold the same volume of air anyways. besides, like stated above, you'd need a 2 pressure regulators (at least) before the parallel air could make it to the pleumatics.

[Pat Fairbank]

Originally Posted by AdamC

Is there a way to hook up your air tanks in parallel, as opposed to series? I understand that the benefits of wiring circuits in parallel, but I doubt it applies to air systems. I would think that the moment a failure occurs in a line that is not cut off by a solenoid, the system would immediately decompress. Any elaboration on this would be very welcome.

To answer your question, yes. There are "T"-shaped connectors which allow you to connect three lengths of pneumatic tubing together.

The only advantage over a "series" connection that this could potentially offer, depending on the layout of your pneumatic components, is a simpler tubing path.

[DonRotolo]

A parallel connection offers lower resistance to flow, meaning higher potential flow rates with less pressure drop in the lines. Although the regulator's single connection is a restriction, unlike hydraulics the gas (air) is sompressible and so the restriction is a point resistance rather than a system resistance. So, you do gain a small advantage in flow rate and available pressure with parallel 'plumbing', at the expense of weight and a little complexity.

To illustrate the restriction issue:

In water pipes, you can run 50 feet of 1" pipe, a foot of 1/2" pipe, and another 50 feet of 1" pipe. The maximum flow is dictated entirely* by the 1/2" pipe.

With Air, using the same setup, the flow is more dictated by overall air velocity, the 1/2" pipe is not much of a restriction at all. (Higher velocities cause more drag in the pipe, which restricts flow).

Don

*the effects of drag in such a case is negligible.

[dtengineering]

While having your high pressure storage tanks in series or parallell doesn't really matter, there are a number of ways to hook up the tanks, some of which may offer advantages. (Note that vent valves and pressure gauges need to be included, too, but aren't shown in the diagrams.)

1) Compressor------tank----tank-----regulator

2) compressor------tank-----regulator
                 |        |
                 ---tank---

3) compressor-----------------regulator
                      |
                       -----tank----tank

4) compressor-----------------regulator
                        |
                        |-----tank
                        |
                        |------tank

These should all work about the same, but methods #3 and #4 offer a reduced amount of tubing should your storage tanks be located somewhere other than in close proximity to the compressor and regulator. Note, of course, that longer runs do mean reduced flow... whether this is significant varies on your system's air demands and tubing lengths and diameters, of course.

You may also want to consider the potential for putting a storage tank downstream of the regulator

compressor-----tank----regulator-----(long tubing)----tank--valve---piston
                                                             |-------|

This may be useful if you need a lot of flow at the piston, but are worried about flow restrictions in the tubing. The air stored in the tank downstream of the regulator would only be at 60psi, but it would be right there, where you need it.

Keep in mind that the valves should be reasonably close to the pneumatic cylinders so that you do not have to vent the tubing as well as the cylinder when you change its position.

Jason

P.S. Hmmm... pardon the dots in the ascii "art" above... but CD seems to keep ignoring the space characters... any tips on how to keep the leading spaces without resorting to dots would be appreciated.

[Daniel_LaFleur]

Originally Posted by dtengineering

While having your high pressure storage tanks in series or parallell doesn't really matter, there are a number of ways to hook up the tanks, some of which may offer advantages. (Note that vent valves and pressure gauges need to be included, too, but aren't shown in the diagrams.)

1) Compressor------tank----tank-----regulator

2) compressor------tank-----regulator
.....................| |
.....................---tank---

3) compressor-----------------regulator
.......................|
.......................-----tank----tank

4) compressor-----------------regulator
........................|
........................ -----tank
........................|
.........................------tank


These should all work about the same, but methods #3 and #4 offer a reduced amount of tubing should your storage tanks be located somewhere other than in close proximity to the compressor and regulator. Note, of course, that longer runs do mean reduced flow... whether this is significant varies on your system's air demands and tubing lengths and diameters, of course.

You may also want to consider the potential for putting a storage tank downstream of the regulator

compressor-----tank----regulator-----(long tubing)----tank--valve---piston
.................................................. ....................................|-------|

This may be useful if you need a lot of flow at the piston, but are worried about flow restrictions in the tubing. The air stored in the tank downstream of the regulator would only be at 60psi, but it would be right there, where you need it.

Keep in mind that the valves should be reasonably close to the pneumatic cylinders so that you do not have to vent the tubing as well as the cylinder when you change its position.

Jason

P.S. Hmmm... pardon the dots in the ascii "art" above... but CD seems to keep ignoring the space characters... any tips on how to keep the leading spaces without resorting to dots would be appreciated.

Each of these setups has advantages and disadvantages, I'll go through each one:

1> This setup allows the highest volume of air to be held, since FIRST rules allow 120 PSI between the compressor and regulator but only 60 PSI beyond the regulator. This setup is best when used in a system where restriction is not an issue but rapid use (continuous cycling) of the pneumatics may deplete the air supply faster than the compressor can supply.

2> This setup sacrifices a little volume for the wider flowpath and moving a volume closer to the application. This setup us good for pneumatics that require short burst / medium volume with a medium cycletime in between uses. This is generally considered the best tradeoff.

3> This setup gives you the least volume of air but puts the volumes right at the application and is good for very short burst / very high volume use applications such as air cannons and such.

4> This is similar to #3 but allows for the volumes to be split between applications, thus allowing 2 very short burst / medium to high volume applications.

Oh, and about long tubing. 1> It's against the rules to add tubing just to add volume (at least it was last year) and 2> adding tubing adds restriction and will actually lower flow rates, unless you run parallel tubing. By the way, when running parallel tubing I recommend using 'Y' fittings rather than 'T' fittings as they restrict less.

For ascii art, you may want to try the 'code' tags.

[dtengineering]

Thanks for the tip on the code tags for the ascii art, Daniel.

I do have a couple of clarifications to make, however. Each of the diagrams numbered 1-4 should have effectively the same volume of stored air, two tanks at 120 psi each. Note that each system can be expanded up to the number of storage tanks allowed, I have just shown two tanks here as an example, and have not accounted for any "extra" high pressure air stored in the longer tubing runs.

Secondly while theory may predict different flow rates downstream of the regulator, I have not done any tests to show whether there is a practical difference in flow and pressure downstream of the regulator between setups #1-4. Perhaps others have? There is probably at least as much difference in flow rates due to tubing lengths and connectors (Y vs. T, as pointed out) and bends in the tubing as there is due to tank arrangement, but even then I don't know just "how much" it takes in order to be significant. I just posted the sketches to show different ways of hooking up the storage tanks on the high pressure side of the system.

The fifth (un-numbered) diagram will store less air, as one tank will be at 120 psi and the other, downstream of the regulator, will be at 60 psi.

Jason

[tseres]

then again, our tem's philosophy is more of "hold as much air as possible and pray it works"

[Daniel_LaFleur]

Originally Posted by dtengineering

Thanks for the tip on the code tags for the ascii art, Daniel.

I do have a couple of clarifications to make, however. Each of the diagrams numbered 1-4 should have effectively the same volume of stored air, two tanks at 120 psi each. Note that each system can be expanded up to the number of storage tanks allowed, I have just shown two tanks here as an example, and have not accounted for any "extra" high pressure air stored in the longer tubing runs.

Secondly while theory may predict different flow rates downstream of the regulator, I have not done any tests to show whether there is a practical difference in flow and pressure downstream of the regulator between setups #1-4. Perhaps others have? There is probably at least as much difference in flow rates due to tubing lengths and connectors (Y vs. T, as pointed out) and bends in the tubing as there is due to tank arrangement, but even then I don't know just "how much" it takes in order to be significant. I just posted the sketches to show different ways of hooking up the storage tanks on the high pressure side of the system.

The fifth (un-numbered) diagram will store less air, as one tank will be at 120 psi and the other, downstream of the regulator, will be at 60 psi.

Jason

I may have misinterpreted your ascii art. I assumed (I know ) that the tank(s) in figures 2-4 were downstream of the regulator.

The small regulators that FIRST has used in the past give ~ 50-60 SLPM flow at 60 PSI output and 120 PSI input. Most applications in FIRST do not need anywhere near that, and if you did (for a short burst) then moving 1 tank downstream of the regulator would give you the added flow (for a very short burst) with the total volume being lower.

[dtengineering]

Originally Posted by Daniel_LaFleur

I may have misinterpreted your ascii art. I assumed (I know ) that the tank(s) in figures 2-4 were downstream of the regulator.

It would have been easy to misinterpret. Thanks to your tip, and Kevin's, I've gone back and tidied it up a bit.

Jason

[FourPenguins]

Unfortunately, your electrical analogy doesn't work, and the reason is this:
In electricity, the force (emf/voltage) is being "pulled" by the difference in charge. It has a bias, one terminal to the other, and it cannot leak (generally, anyway). In pneumatic systems, force is applied equally in all directions, so when one direction is open, this is the path of least resistance. If a leak opens, this path has very little resistance and the air follows this path. The only way your series design would work would be if there were some way to isolate the ruptured tubing once a leak was detected.
Sorry