Pinch valve question?

[Bill Baer]

Originally Posted by Adger Smith

I have always wondered if you use a pinch that is open to atmosphere if it is subject to Baro changes.

Well considering that the air pressure on the pressurized side is 80 psi and a change of 1" in the barometer is 0.486 psi it would take a barometer change of 2" to change the pressure differential 1% so while barometric pressure does make a difference it's not a significant one.

[Adger Smith]

Bill,
That is about the same conclusion I had when dealing with % of air pressure, but the actual air pressure coming out of the pinch is not the same as the 80 psi in the cylinder.
Also: How do you account for time and vol. as variables?
Or do you/should you?
Is this something that causes a quicker dump to be more consistant than a slow one?
I'm thinking it would be more consistant to pressure feed on both sides of the cylinder with regulated pressure differences.

[Bill Baer]

Originally Posted by Adger Smith

Bill,
That is about the same conclusion I had when dealing with % of air pressure, but the actual air pressure coming out of the pinch is not the same as the 80 psi in the cylinder.
Also: How do you account for time and vol. as variables?
Or do you/should you?
Is this something that causes a quicker dump to be more consistant than a slow one?
I'm thinking it would be more consistant to pressure feed on both sides of the cylinder with regulated pressure differences.

Adger
Actually the pressure coming out of the pinch valve is the same as the cylinger but the restriction provided by the pinch valve increases the amount of time it takes to fill the volume on that side of the cylinder and slows the throttle opening. There is little or no restriction in the throttle closing (Dumping) side.
The volume is fixed by the diameter and stroke of the air cylinder and the time to fill that volume thru a restriction should also be fixed if the pressure remains constant but, the data frm my throttle position sensor incicates that that latter time of strokeis not fixed and does vary somewhat.
I'm starting to question if the opening side might work more consistently if it had litle or no restriction.
I suppose you could try to feed different pressures to different sides of the cylinder but you have to keep the pressure high enough to work solidly So I don't think a lower pressure would do the mechanical work properly.