If we do not not need to it to push out, and just need the returning motion, can we leave the air input hole open. We are wondering if we can leave the piston disconnected from the resevoir to absorb air from the outside using some things (such as rubber bands and a lever) to push out. We have questions mainly if this would work, and especially if it is legal.
As Kevin said, this is perfectly legal and lots of teams do it. If you have a double acting cylinder, then you probably also have a double acting solenoid…you’ll have to plug the extra port on the solenoid…unfortunitely the push-to-connect plugs we use in industry for this purpose are not legal vex parts, so you have to use some tubing and tie a knot in it, or connect it to a closed valve, or to a tee fitting and add another loop to plug the other two sides of the tee off, or some other creative way that you’ll think of.
I usually suggest to teams to double back the tubing along itself and then putting a zip tie as tight as possible holding it closed. Remember any tubing after the soleniod is air volume you lose every stroke.
You would leave the hole on the pneumatic cylinder open, but not on the solenoid valve. If you did, you would empty your air supply out the hole! When the cylinder is retracted by your rubber bands, air will enter the cylinder through the open hole as the piston moves within the cylinder. When you actuate the cylinder, the air will blow out that same hole.