Does Max PSI Apply to the vacuum?

[sonofdad123]

Just wondering-
Does the 60psi max apply to the vacuum generator/suction cup also? Dad and I were just puzzling over it and couldn't come to a sound conclusion after discussion and perusing the threads. Help?

[karlcswanson]

I think any pneumatic device on the robot must operate at 60 PSI, 120 psi is allowed just for storage.

<R104> “Working” air pressure on the ROBOT must be no greater than 60psi. All working air must
come from 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.

[Kevin Sevcik]

..... Just out of curiosity, how were you planning on getting more than about -15 gauge psi out of a vacuum? Pressure at sealevel is about 15 psi, so a perfect hard vacuum is going to be -15 gauge psi at best. So, basically, you can't even approach the 60 psi limit, so don't worry about thing on the vacuum side of the equation.

The 60 psi limit does apply to the high pressure side of the vacuum generator, since the 60 psi limit applies to any working air on your robot. Only the air in the storage tanks can be over 60 psi.

[Jeff Rodriguez]

I would say that vaccums are not subject to pneumatic rules:
Section 8.3.10 - R106 - For the purposes of the FIRST competition, a device that creates a vacuum is not considered to be a pneumatic device and is allowed. This includes, but is not limited to, Venturi-type vacuum generators and off-the-shelf vacuum devices (as long as they are powered by one of the Kit-of-Parts motors).

They are however subject to the laws of nature. The maximum pressure you can get from a vaccum is 14.7 PSI, atmophereic pressure.

I think I actually learned something in school.

[dtengineering]

The 60 psi rule certainly applies to the line feeding pressurized air to the vacuum pump.

From my readings of the specs that came attached to the pump, it seems to say that it generates maximum suction (ie minimum pressure) when fed with a 26 psi feed. Our experiences seem to suggest it likes quite a bit more than that, but we may have some tweaking yet to do.

In any case, you may find that regulating your pressure down to 26psi not only provides you with sufficient vacuum, but reduces draw on your compressor and battery.

Jason

[sonofdad123]

thanks everyone :-)
i guess the specs that came with the box got lost somewhere... probably in the same spot as my socks that vanished in the washing machine

[billbo911]

I may be way off my nut here, but I think there is something that needs to be discussed here.
To maintain a vacuum with these vacuum generators, air must be flowing continuously through the generator. Once the airflow stops, the vacuum dissipates and things (like tubes) fall off . If you are feeding the generator through your clippards, I believe you will quickly run out of capacity and be running off a continually running compressor. Does this sound right or am I missing something?

[DonRotolo]

Originally Posted by sonofdad123

thanks everyone :-)
i guess the specs that came with the box got lost somewhere... probably in the same spot as my socks that vanished in the washing machine

Those get turned into coat hangers...

Originally Posted by billbo911

I believe you will quickly run out of capacity and be running off a continually running compressor. Does this sound right or am I missing something?

Almost. The key figure is the air consumption, which is something like 0.38 CFM at 26 PSI. Now, if you find the volume that the compressor can deliver (when brought down to 26 PSI) that'll tell you how hard the compressor will have to work. (Hint: it's not 100%).

If you use the vacuum, you can turn it off with a solenoid valve when you don't need it (also, how will you release the tube without a valve??). Vacuum off means no air consumption, right?

On a related note: In 2005 when we used pneumatics, the compressor essentially ran 100% of the match, so count on that. Note that even with 4 small CIMs, a compressor, and more, the batteries have the power.

Don

[kmcclary]

Originally Posted by Don Rotolo

If you use the vacuum, you can turn it off with a solenoid valve when you don't need it (also, how will you release the tube without a valve??). Vacuum off means no air consumption, right?

On a related note: In 2005 when we used pneumatics, the compressor essentially ran 100% of the match, so count on that. Note that even with 4 small CIMs, a compressor, and more, the batteries have the power.

Don

(Vacuum off means no air consumption, right?) Correct. You turn it off with a valve connected to the pressure input port of the vacuum generator. The generator's output is connected directly to the cup.

(How do you release the tube?)

(1) Just turn off the pressure input! The vacuum is generated by the Venturi Effect. Think about when you blow across the top of a straw that is in a drink cup. A vacuum is generated in the straw's column from the rapidly moving airflow across its top opening. But what happens? The fluid rises ONLY as long as you are blowing. When you cut off the pressure, air zips back in along the tube, and the column of fluid drops like a rock. Similarly, without suction, the vacuum in the green tubing bleeds out rapidly (from the generator end). No vacuum, no holding force. Then, the Ringer's weight (or your robot pulling back) separates the cup from the Ringer.

(2) In industry, for faster action you add a "blow off" connection. This injects a bit of air to "eject the held object". That can easily be done here by adding a second valve to provide air in the link between the vacuum generator and the suction cup. BUT, if you keep the vacuum generator to suction cup line short, it probably will NOT be needed.

Now if you don't like the speed and DO decide to add a blow-off connection, be sure to keep the pressure as low as you can that still allows the (piloted) valve to reliably operate. That'll probably be in the 20-35PSI range. After all, you don't need much air at all, just a tiny puff! You may also wish to consider adding a flow regulator to the valve's output, just to reduce the airflow further. BUT REMEMBER, if you quickly change your mind about gripping and try to grab again right away, it MAY take a fraction of a second longer to grab. (After all, you may have to purge the additional blow-off air you just injected.)

BTW... Don't forget to plug the other (normally closed) output side of the blow-off valve! (Failure to do this should become obvious pretty quickly, when all your compressed air escapes... Hee Hee...)

Now I seriously doubt that you'll need a blow-off connection for this application. That's one of the main reasons FIRST provided such a tiny connection tubing for the suction cup. The total volume of air it takes to refill the vacuum line is VERY small. The instant you turn off the air supply to the generator, room air should rush back in along the green line (from the generator's end) in a flash.

Does this answer your question?

- Keith