Hello everyone, I have an electric hydraulic press that Im looking to work with. It works in the following manner; two buttons must be pressed at the same time on either side of the machine, and once they are, power is supplied via a single wire to an air switch, which then lets our shop air supply activate a pneumatic cylinder that moves the "transmission" valve on the hydraulic unit. Thus, the ram moves down while the buttons are pressed. When the buttons are released, the air switch goes back, pressure releases from the air cylinder, and the ram returns to its home (up) position and stops.

What we are trying to do is add two proximity switches to this circuit so that the ram can be automatically stopped when the lower proximity switch is tripped, but not allow the buttons to work again until the upper proximity switch is tripped.

Basically, I need a circuit to cut the button feed when the lower switch is tripped (it would be just like letting go of the buttons), but the buttons must stay disabled until the upper switch is tripped. What I foresee happening if I dont do it this way is, the lower switch will trip and cut power to the buttons so the ram starts its travel up, but as soon as it clears the lower proximity switch, it will start back down if the buttons arent released. The ram moves very quickly and at a distance of only a few inches, so that isnt really an option.

What I think I need is a type of latching relay system so that once the lower switch is tripped, the relay continues to cut power from the buttons until the upper switch is tripped. Id like to keep this as simple and easy to do as possible, with repair parts readily available as this is a production machine.

The proximity switches I have been tasked to use for this project are (1) normally open switch, and (1) normally closed switch. Both have 110 VAC input (like the rest of the controls on the machine), one output, and ground. They do have tags on them to warn to use series load resistors even when bench testing to limit current to 0.3 amps. Im sure the air switch (which is what Im ultimately trying to control) is less than that easily, do I still need to worry about the load resistors?

Thanks in advance!