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Last time, we learned how a solenoid valve operates to create different compressed air flow paths through passageways within its valve body. These different air flow paths are created by opening and closing an electrical switch to de-energize and energize a solenoid mounted on the valve body. Now let’s see how engineers use a solenoid valve in a food manufacturing plant to move a depositor’s pneumatic actuator piston back and forth with compressed air pressure. Consider the pneumatic actuator on the depositor’s scotch yoke. With the solenoid valve’s electrical switch opened, the valve’s spool is pushed up in the valve body by a spring to create air flow paths between Ports A and E and Ports D and B. If compressed air is fed into Port A and the left side of the pneumatic actuator’s cylinder is connected to Port E, then the air pressure moves the actuator’s piston to the right. But, for the actuator piston to move freely to the right, the right side of the cylinder is connected to Port D on the valve body. As the piston moves to the right, it forces air out of the right side of the cylinder, through Port D, through the valve body, and out through Port B to be vented to the atmosphere.
The De-energized Solenoid Valve Operates a Pneumatic Actuator With the solenoid valve’s electrical switch closed, the spool is pushed down in the valve body by the solenoid, to create air flow paths between Ports A and D and Ports E and C. If compressed air is fed into Port A and the right side of the pneumatic actuator’s cylinder is connected to Port D, then the air pressure moves the actuator’s piston to the left. But, for the actuator piston to move freely to the left, the left side of the cylinder is connected to Port E. As the piston moves left, air is forced out of the left side of the cylinder, through Port E, and vented to the atmosphere through Port C. The Energized Solenoid Valve Operates a Pneumatic Actuator So, in review, opening the solenoid valve’s electrical switch causes the pneumatic actuator piston to move right. Closing the switch causes the piston to move left. But there is a problem with this setup. Operating an electrical switch by hand to deposit jelly filling on thousands of pastries can get tiring after a while. Next time, we’ll see how the valve’s solenoid can be automatically turned on and off by an industrial control system. Copyright 2018 – Philip J. O’Keefe, PE Engineering Expert Witness Blog ____________________________________ |
