Solution: Variable position of cylinder in compliance with <R74>

[sanddrag]

I started reading this, and it seemed so complicated I just gave up. I don't typically give up at understanding things, but this just seems like so complex of a system, that perhaps the design should be reconsidered if it requires all this. Motors anyone?

[DonRotolo]

Originally Posted by sanddrag

I started reading this, and it seemed so complicated I just gave up. I don't typically give up at understanding things, but this just seems like so complex of a system, that perhaps the design should be reconsidered if it requires all this. Motors anyone?

I'm normally a guy who understands stuff, but I'm also lost here. I'd need to see it I guess.

How about a mechanical stop for that 'middle' position? A tiny servo moving a locking pin/bar could manage that.

[sanddrag]

After reading this a second time, I totally get it now. In theory, it's actually a rather nifty idea. Not nearly as complicated as I thought. In practice, I think it would leave a lot to be desired.

[Roboman01]

The valve in the schematic above is a 5-port, 4-way, 3-position valve with the center position blocking both pressure and exhaust ports. This allows the pneumatic cylinder to be controlled similarly to a hydraulic ram, since one can shut off and trap the air inside the cylinder, preventing significant movement.

Of course, <R73> specifically states that this is not allowed, so one must be able to vent the trapped pressure at the same time as the rest of the system, from a single valve. The two check valves allow this. Each check valve allows air to flow (mostly) unobstructed out of the supply to each cylinder, but does not allow the high-pressure air to reach the cylinder supply lines. Since the pressure in the cylinder is lower than that of the accumulator, little air will be lost, due to the natural tendency for the higher pressure air to seal off the check valve.

During normal operation, this will cause the cylinder to act as if it were connected via a normal piece of tubing. However, in the event that we need to vent all of our stored pressure rapidly, the check valve will allow the stored pressure in the cylinder to flow straight out the dump valve.

[DonRotolo]

Oh, I get it - the check valves allow the whole system to vent to atmosphere when high pressure is released, thus making the 3-way valve (center position blocking) legal.

I'd be prepared to explain carefully to the inspector why the high pressure side seems to be connected to a cylinder.

[PAR_WIG1350]

Just to clarify, the system explained in the first post and the schematic in the second are actually 2 very different methods of controlling cylinders. I imagine it would be very difficult to try to match the schematic to the description in the first post, since they don't actually go together.

[Roboman01]

I imagine it would be very difficult to try to match the schematic to the description in the first post, since they don't actually go together.

That was the point. I was trying to describe a simpler system of controlling the cylinder.