Disc Rotary Valves are used to operate Pneumatic Cylinders. In the absence of electrical supply, manually operated valves such as Hand Lever Valves are used. The functioning is the same, however, the solenoid coil is replaced by a hand lever, which controls the movement of the spool inside the valve, thereby allowing the air to pass.

3/2-Way Pneumatic Valve – How They Work.

A 3/2-way valve has three ports and two positions that can be driven pneumatically, mechanically, manually or electrically via a solenoid valve. They are used, for example, to control a single-action cylinder, driving pneumatic actuators, blow-off, pressure release and vacuum applications. A valve is used to fill the cylinder, and also to exhaust it afterwards, so that a new working stroke can be realized. Therefore, a valve with two ports would not be adequate. Venting requires a third port. There are two kinds of 3/2 valves: mono-stable and bi-stable. Mono-stable 3/2-way valves can also be normally closed or normally open, just like 2/2-way valves. Link to a video explaining how a 3/2 Hand Lever valve operates.  Click here to get 5/2 or 5/3 way Hand Lever Valve Click here for Airmax RM series 3/2 way Hand Lever Valve Click here for Janatics make Hand lever valve.