Air Tanks

[geo]

Can someone tell me what is the max pressure can an air tank hold??

Thanks

[Joseph F]

dont let the system exceed 120psi. For safety and most purposes 110-115 psi is more than enough.

[f22flyboy]

but hypothetically , what are the tanks rated for?

[Jnadke]

Clippard's website says they are rated for 250psi...

It should say it in the pneumatics manual, read it:
http://www2.usfirst.org/2002comp/pneumatics_manual.pdf

[rbayer]

The tanks may be rated for 250 as are all of Clippards tanks, but I don't believe the cheap plastic hosing is rated that high as most is only rated for 150 at the most. Besides, the compressor has a relief valve at 120psi so you'd never get there anyway.

[hot69z]

when i went to the FESTO pnewmatic workshop last year there was a large discussion on the general parts we would be "most likely to recive" the plastic tubing is rated for 160 PSI. The tanks are most likely can take 250 psi. But FIRST limits us to a meger 60 psi before it gets to the tanks. With any luck it will be bumped up to a much more powerfull PSI this year, that would make a world of differance.

[Jnadke]

FIRST allows 120PSI all the way to the accumulators (air tanks). This is plenty and within the specification of the manufacturer.

Mind you, the maximum pressure he said above is 160PSI for the tubing. Approaching this value is not recommended and is an unnecessary risk.

The working pressure is set at 60PSI for safety reasons. The 2" bore cylinder can pressurize to 188 pounds of force according to the manual. This is plenty for all practical applications, such as lifting a robot (or goals). Any more than that is unnecessary and dangerous.

[f22flyboy]

FIRST rules limit us to 120psi to the accumulator and 60psi at working circuits, so that is the setting on the relief valves when we recieve them. However, these components are designed to work at 250psi, so the relief settings can be easily changed. After a little research i have descovered that the weak link in the tubing is the connections, which are rated to work at about 150psi. Usually pnuematic products are rated at less than 1/3 of their limit.

The next question is: Is FIRST paranoid?

they limit all working circuits to 60psi so that if someone managed to "stall" a piston, by somehow providing over a 180lbs of back pressure (for the 2" piston), the pressure in the system could hypothetically double, raising it to 120psi. This is still way under the safe operating range, and the circumstances described would be nearly impossible to create. So why does FIRST restrict us so much?

Also, would increased psi increase the speed of the 3/4" piston?

[Lloyd Burns]

Originally posted by f22flyboy
However, these components are designed to work at 250psi, so the relief settings can be easily changed. Usually pnuematic products are rated at less than 1/3 of their limit.

Don't confuse Working with maximum pressure. In Machine Elemants 101, you learn that Steel has an 'Ultimate Yield Strength', and an 'Elastic Limit' and you learn that prudent design posits a 'Safety Factor' which permits using in your design only a fraction of the limits. The Elastic limit is the max stress at which the steel can still return to its normal dimensions, but many cycles of this would weaken it (another limit!). Ultimate is the strength at which the steel breaks, and an encounter with this much stress is unrecoverable.

In pneumatics, working pressure is akin to the stress allowed after the safety factor is applied. It is the manufacturer telling you what works for millions of cycles, and should not be exceeded lightly.

The next question is: Is FIRST paranoid?
(T)hey limit all working circuits to 60psi so that if someone managed to "stall" a piston, by somehow providing over a 180lbs of back pressure (for the 2" piston), the pressure in the system could hypothetically double, raising it to 120psi.

If you ran your robot at full speed into a wall, with a piston extend forward, the robot would push the cylinder, raising the pressure in the cylinder, the tubing, the valve, more tubing and back to the regulator, at which point, the regulator would open the pressure system and bleed off the excess pressure, perhaps more slowly than need be for a large cylinder. The system pressure would spike, then return to the regulated pressure.

Also, would increased psi increase the speed of the 3/4" piston?

We've found that we can never get pneumatics to move *too fast* on the robot - If your goal grabber takes a xecond to close, that is the second someone else steals the goal ! The speed depends on load and on tank capacity, as well as pathway area for the air. After we had extended our arm using a foot-long 2-in cylinder, on the reservoirs we had last year, our 1.5-in, 5-in long jaw closers were gasping for air, and the pump had to come on. You can use up the air in your tanks, lower pressure, and have your actuators slow down under whatever load.

If the 3/4" cylinder under light load is the only pneumatic actuator on your robot, and you have lotsa reservoir, then yes, more pressure equals more speed, although the increase would be less noticeable with a flow restrictor ("in both ends (!!?!!)") slowing it down.

However, a 3/4" piston can be quite viscious at 60 psi: do you need more pressure, or just a better design ?

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