The Alma Piston Digital Control Valve basically consists of a spring loaded piston, sliding in the guide liner, and two solenoid valves. Piston chamber formed between the liner and the piston top, is connected to the upstream and downstream pressures by normally open (NO) and normally closed (NC) solenoid valves respectively.
When the Piston Digital Control Valve is used with an electronic batch controller, it can be digitally controlled by operating the solenoid valves through any of these three stages :