Another pneumatics question

[DPPT1717]

Is it legal to run a piston off a compressor without running it through a tank?

[eshteyn]

i dont see why not as long as you follow all regulations stated in rules <r99> to <r106>, also you really dont want to run the bimba off of just the compressor, the tank would give u fast movement for the bimba as well as repeated movement on a full tank

[DanDon]

Originally Posted by DPPT1717

Is it legal to run a piston off a compressor without running it through a tank?

Let's start with this: why do you want to run the piston straight off of the compressor? Maybe we can help with your implementation of the pneumatic system.

[eshteyn]

Originally Posted by dhoizner

Let's start with this: why do you want to run the piston straight off of the compressor? Maybe we can help with your implementation of the pneumatic system.

He is right, we would love to help you build your system.

[Kevin Sevcik]

It is legal. The minimum system is a set of gauges to show stored and working air pressure, and a relief valve to vent any stored pressure to atmosphere. You would also have to put the 60psi main regulator between the compressor and the pressure switch to turn off the compressor at 115 psi.

As eshteyn said, you'd really want a volume tank in there, though, or you'd have to wait for the compressor to fill up the piston each time you moved it. If you're worried about weight and you're only using a few small pistons, you might consider only using 4 volume tanks and keeping the compressor off your robot. You'd have a limited amount of air and number of piston firings to work with, but if you know how much you need precisely enough, you could make it work.

[SuperBK]

Shouldn't the pressure switch be before the regulator, in other words "put the pressure switch between the compressor and the regulator to cut the compressor off"
Brian

[Mike Hendricks]

At the very least, I would reccommend using one tank. It isn't going to add THAT much weight (as much as, say .. 4 tanks), and your cylinder movement is going to be much smoother.

As for 4 tanks vs the compressor, I would take the compressor and one tank. Depending on the application of course. If you're using this just to shift a pair of transmissions with a .75" bore 1" stroke piston .. then go with the tanks. If you're moving a 1.5" bore 18" stroke piston on an arm .. then maybe you should consider the compressor.

And the pressure switch needs to go before the main regulator. If it wasn't, you'd never get past 60psi, and the compressor would run until the relief blew. Not smart.

[Joobacca]

it is not to your advantage to not use a reservoir coming from your compressor. it allows for more pressure to be store before going out to your actuators and stores air in the system for when you aren't using the pneumatics. it's sort of standard to use tanks. you're thinking though!

[kmcclary]

Originally Posted by Joobacca

it is not to your advantage to not use a reservoir coming from your compressor. it allows for more pressure to be store before going out to your actuators and stores air in the system for when you aren't using the pneumatics. it's sort of standard to use tanks. you're thinking though!

There's another reason to use as many tanks as is allowed: You can precharge the tanks before the round.

Consider: The total amount of work (in the physics sense) allowed in a FIRST pneumatics system equals (A) whatever you can compress during the round, PLUS (B) whatever energy was stored in the tanks before the round.

Therefore, to maximize this value you want to go into the round with the largest storage volume allowed, prefilled with compressed air stored at the maximum PSI allowed!

Now OTOH, the compressor, its spike, the control hardware (et al) all cost you in weight. Therefore, IF you are using only a tiny amount of air during the round (such as the only pneumatic device is your "end of round release trigger widget", or "pneumatic gear shifting" with tiny cylinders and little work will be done), then by all means delete the compressor and drive the pneumatic load with just the storage tanks precharged to their max pressure.

A few caveats though:

1) All FIRST supplied valves are 'piloted'. They use air to either maintain their state (every 'spring return type' of valve in the kit), or require a minimum pressure to exist to switch state (such as the SMC dual coil type valve).

Example - Try this out: Build up the compressor component. Attach the "grey" (Festo) valve as directed with any cylinder as a "load". Turn it on by putting 12VDC onto its contacts. NOW, slowly reduce the input air regulator's setting... You'll quickly discover that although the coil to the valve is still "on", once the pressure drops low enough (somewhere in the 20-35 PSI range) it WILL suddenly switch to the "off" state! The spring return "becomes stronger" than the "hold" pressure, and it switches off although the light is still on! With the dual coil SMC valves, you may find that you can no longer switch state once the tank pressure has dropped too far.

(I do this demo with every incoming rookie class to our team, to impress upon them the need to tinker and try things out, as some devices in the kit may not act as you think!)

FYI, if you check the specs, most of the valves in this contest state they they need somewhere around 35 PSI minimum input pressure to operate. So, if you're contemplating a "tank only" system, your total consumption should never allow the tank pressure to drop below that value at any time during the round, or else unpredictable behavior may occur.

2) Avoid using the vaccum generator with a tank-only system! The unit continuously consumes air to generate and maintain vacuum. That means you'll only have a VERY limited number of "grip-on" seconds in total. (I think it would be mighty embarassing to drop your Ringer while you're still jockeying for position, and not be able to pick it up again!)

3) To maximize total actuations possible, minimize the total cylinder volume of your loads, by picking the absolute minimum bore and stroke required to get the job done. After all, every time you actuate a cylinder (in either direction), you "throw away" it's total displacement volume of air. In an air-limited application, that could become important.

I hope this helps!

- Keith