Posts Tagged ‘solenoid valve’

The Solenoid Valve Operates a Pneumatic Actuator

Monday, August 6th, 2018

    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

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

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

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The Solenoid Valve’s Operation

Monday, July 30th, 2018

    Previously, we looked at the components of a solenoid valve, which is an electro-mechanical device that is commonly used by engineers to operate pneumatic actuators with compressed air.   These solenoid valve components include a solenoid and a valve body.   We also looked at an illustration of an example solenoid valve.   Its valve body had five ports for connections to compressed air pipes.   Now, let’s see how the example solenoid valve operates to create different compressed air flow paths between its ports.

    When the solenoid valve’s electrical switch is opened, the flow of electrical current from its 120 Volt supply is interrupted.  This results in the solenoid’s wire coil being de-energized.   As such, the coil generates no magnetic field.   Without the magnetic field, there is no downward force exerted on the solenoid’s plunger and the valve body’s spool.   A spring at the bottom of the valve body acts upon the spool to force it upward in the valve body and hold it there.   With the spool in the upward position, two compressed air flow paths are created in the valve body.   One path extends through a passageway connecting Ports D and B, and the other extends through a passageway connecting Ports A and E.   The spool seals off the passageway leading to Port C.

 The Solenoid Valve’s Operation: Energized

The Solenoid Valve’s Operation: De-energized

    When the electrical switch is closed, the 120 Volt supply is connected to the valve’s solenoid.   This results in the solenoid’s coil becoming energized.   When that happens, the electrical current flowing through the coil generates a magnetic field.   The magnetic field forces the plunger and spool in the downward direction.   The spool overcomes the spring force and moves into a downward position within the valve body.   In this position, the spool creates a new pair of compressed air flow paths.   These paths remain as long as the current flows through the solenoid’s coil.  One compressed air flow path extends between Ports A and D.   The other path extends between Ports E and C.   The spool seals off the passageway leading to Port B.

 The Solenoid Valve’s Operation: Energized

The Solenoid Valve’s Operation: Energized

    When the electrical switch opens, the solenoid’ coil again becomes de-energized.   The magnetic field collapses, and no downward force remains on the plunger and spool.   The spring forces the spool back up in the valve body.   Once again, a pair of compressed air flow paths is created between Ports D and B, and between Ports A and E.   The passageway to Port C is sealed off by the spool.

    Next time, we’ll see how the example solenoid valve’s operation is applied to move the piston back and forth in a depositor’s pneumatic actuator.

 

Copyright 2018 – Philip J. O’Keefe, PE

Engineering Expert Witness Blog

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The Solenoid Valve’s Components

Monday, July 23rd, 2018

    So far in this series of articles, we have talked about pneumatic actuators that move jelly filling through a depositor on a pastry production line in a food manufacturing plant.   These actuators have pistons with piston rods that create linear motion.   The direction of this motion depends on which side compressed air is admitted to the piston inside the actuator.   Now, let’s begin discussing a device known to engineers as a solenoid valve.   These valves are used to selectively admit compressed air to either side of the pneumatic actuator’s piston, and thus, change the direction of the actuator’s linear motion.

    As a solenoid valve’s name implies, a key component is a solenoid.   A solenoid consists of a tube, having a coil of wire wrapped around its exterior.   Electrical wires extend from the coil to an electrical switch and a voltage supply of, for example, 120 Volts.   Inside the tube, there is a steel plunger that is free to move.    When the switch is open, the coil is de-energized.   That is, no electric current flows from the voltage supply through the coil of wire.

 A De-Energized Solenoid

A De-Energized Solenoid

   

    When the electrical switch is closed, the coil becomes energized. As electrical current flows through the coil, a magnetic field is created in the tube.   This field forces the steel plunger out of the tube.  The magnetic field and force on the plunger remain as long as the switch is closed.

An Energized Solenoid

An Energized Solenoid

   

    A solenoid valve consists of a solenoid that is attached to a metal valve body.   The solenoid is typically enclosed in a plastic or metal housing.   The valve body contains various ports.   The ports are threaded holes for the connection of compressed air pipes.

A Solenoid Valve

A Solenoid Valve

   

    The solenoid’s plunger is attached to spool in the valve body.   The spool is free to move within the valve body past passage ways extending from the ports.   In the following illustration, the solenoid valve contains five ports, designated A through E.

 

The Solenoid Valve’s Components

The Solenoid Valve’s Components

   

    Next time we’ll see how the five port solenoid valve operates to create different compressed air flow paths between its ports.

 

Copyright 2018 – Philip J. O’Keefe, PE

Engineering Expert Witness Blog

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The Depositor’s Scotch Yoke Motion

Monday, July 16th, 2018

    In my previous article, I introduced a mechanism known to engineers as a Scotch Yoke.   It converts linear motion of a pneumatic actuator into rotary motion.   With regard to the jelly filling depositor on a pastry production line, the Scotch Yoke converts the pneumatic actuator’s linear motion into the rotary motion needed to operate the depositor’s diverter valve.   Now, let’s follow the Scotch Yoke’s motion in this application.

    When the pneumatic actuator’s piston is all the way to the left, the Scotch Yoke’s slider is all the way to the left on the guide rod.   The slider pin is at the top of the slot in the yoke mechanism.   The diverter valve is positioned to create a path for the jelly so it can be emptied from the pump through the nozzle.

 The Depositor’s Scotch Yoke

The Depositor’s Scotch Yoke Slider Is Full Left

   

    As compressed air is introduced to the left side of the actuator’s piston, the piston moves to the right, and the slider also moves to the right.   As this happens, the slider pin begins to move in the yoke mechanism’s slot, and the diverter valve shaft begins to rotate clockwise.

The Depositor’s Scotch Yoke Clockwise Rotation

The Depositor’s Scotch Yoke Clockwise Rotation

   

    After the piston moves all the way to the right, and the diverter valve shaft stops its clockwise rotation.   The diverter valve is positioned to create a path between the pump and hopper so the pump can suck in jelly from the hopper.   When the pump is full of jelly, compressed air is introduced to the right side of the piston.

 The Depositor’s Scotch Yoke Slider Is Full Right

The Depositor’s Scotch Yoke Slider Is Full Right

   

    As compressed air is introduced to the right side of the actuator’s piston, the piston moves to the left, and the Scotch Yoke’s slider also moves to the left.   As this happens, the slider pin begins to move in the yoke mechanism’s slot, and the diverter valve shaft begins to rotate counterclockwise.

 The Depositor’s Scotch Yoke Counterclockwise Rotation

The Depositor’s Scotch Yoke Counterclockwise Rotation

   

    After the piston moves all the way to the left, the diverter shaft stops its counterclockwise rotation.   The diverter valve is once again positioned to create a path so the jelly can flow from the pump through the nozzle.   After all the jelly is emptied from the pump, compressed air is introduced to the left side of the piston to repeat the previously described motion.

    But what selectively admits compressed air to either the right or left of the pneumatic actuator’s piston?   Next time, we’ll find out when we discuss a device called a solenoid valve.

Copyright 2018 – Philip J. O’Keefe, PE

Engineering Expert Witness Blog

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