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Join Date: May 2010
Posts: 1

Fast Switching Cv=>2.5 Pneumatic Valve

09/17/2010 8:27 AM

I am looking for a very fast acting Cv=>2.5 pneumatic valve in a 5/2 configuration and 100 psig line operation. I am operating a double acting cylinder and could use other valve configurations to accomplish an effective 5/2 operation. I have been looking at dual solenoid (internal or external pilot) spool valves as well as direct acting small valves to pilot poppet or spool main valves. Bottom line is that with pressure sensor screwed directly into the valve ports, my best directional switching time is about 28msec (regardless of manufacturer's spec.) to 90% pressure. Any suggestions on valve type or manufacturer welcome. Thanks

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Anonymous Poster
#1

Re: Fast Switching Cv=>2.5 Pneumatic Valve

09/17/2010 8:46 AM

Hi, John

consult your local supplier, Fisher / Masonielan / James Burry / Foxboro / etc.

Regard's

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#2

Re: Fast Switching Cv=>2.5 Pneumatic Valve

09/17/2010 9:17 AM

It sounds like you need a dump valve :http://www.peterpaul.com/valve_info.php4?valve_type=HF#series70

If that is not enough you could parallel them.

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Anonymous Poster
#3

Re: Fast Switching Cv=>2.5 Pneumatic Valve

09/17/2010 10:07 AM

Did you try QRVs (Quick release valves?) You may Check up with Rexroth Bosch website

UD15

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Commentator

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#4

Re: Fast Switching Cv=>2.5 Pneumatic Valve

09/17/2010 11:31 AM

You're looking for a directional control valve, try Norgren, they specialize in pneumatic control solutions and these types of valves are a well known product of theirs.

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#5

Re: Fast Switching Cv=>2.5 Pneumatic Valve

09/17/2010 11:49 AM

The shortest time is obtained with single acting valves since the time to fill up the actuator of the second stage increases the whole commuting time.

There is a trick to obtain higher magnetic forces and thus shorter times.

In general DC solenoids are designed for the thermal load at 100% duty cycle.

The trick is to use a higher supply voltage to push faster the current through the solenoid but for a limited time: use a high voltage pulse long enough to move the spool or the core and then decrease the current to maintain it only in the controlled position. In general the current required to maintain it in actuated position is a lot less than the one required to obtain the movement.

If the thermal load considering this double level cycle does not exceed the nominal design load there is no influence on the duty life of the valve.

Time reductions can be very important. You should use 4x 2/2 Valves normally closed to obtain the control of a double acting cylinder.

The current control via the applied voltage can be either over time or a more complex one via the core position in the solenoid. This can be determined without any stroke sensor by impedance measurements.

You may only consider that higher speeds will generate more important shocks on seats and may be a higher wear rate.

I used this approach many years ago and had > 50% reduction. The valve was delivered with coils for 12V and used with voltage supply 24V and over.

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#6
In reply to #5

Re: Fast Switching Cv=>2.5 Pneumatic Valve

09/18/2010 1:03 PM

G.A...
It may however be possible to obtain higher wattage coils @ the required voltage to replace the originals ...thus negating the need to overvolt.

Regards Woody

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Power-User

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#7

Re: Fast Switching Cv=>2.5 Pneumatic Valve

09/18/2010 3:45 PM

John if we cut to the chase you probably want to operate your cylinder rapidly and are focused on the valve rather than the whole picture.

The exhausting air from a cylinder controls the cylinder speed as evidenced by meter out flow controls. Therefore any attempt to achieve top speed of a cylinder should consider the exhaust path.

Then a pair of 3/2 valves with a generous Cv to exhaust close coupled to the cylinder ports on either end can be helpful. Poppet valves often have higher flow to exhaust than from inlet to cylinder port.

If the cylinder does not hold a load once extended or retracted use position sensors and exhaust or reduce the supply driving the cylinder when it completes the stroke. The retract pressure will drive the piston against zero or low resisting pressure. A 5/3 valve with cylinder ports exhausted in center position works well for this. The Norgren ISO Star, on ISO #3 base with direct acting Solenoids would be my choice.

Be prepared for a cylinder that may travel so rapidly that it may break.

If you must use a 5/2 valve:

Increase the Cv, especially for exhaust flow.

Keep plumbing generously sized, (Cv greater that the valve), short and use full flow push to connect fittings. The smallest passage will control the flow so one unfortunately sized item negates all the rest.

Generally DC Solenoids are slightly faster than AC and someone mentioned the advantage of a high watt coil. It takes energy to produce rapid motion.

Tom

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#8
In reply to #7

Re: Fast Switching Cv=>2.5 Pneumatic Valve

09/18/2010 4:21 PM

The advantage of using 4x2/2 valves is that as function of stroke you can open or close as you need either to accelerate or to brake. This can allow a high acceleration and a high speed coupled with an optimal braking at stroke end so that the piston does not hammers at stroke end. This is especially important when the piston moves a mass not only works against a force. The solution which is only based on a low outlet resistance is very good for punchers or riveting or similar operations but not for positioning.

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