Archive for July, 2018
Monday, July 30th, 2018
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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: 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
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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Tags: air flow path, compressed air, depositor, engineering, magnetic field, plunger, pneumatic actuator, ports, solenoid, solenoid valve, spool, valve body
Posted in Engineering and Science, Expert Witness, Forensic Engineering, Innovation and Intellectual Property, Personal Injury, Product Liability | Comments Off on The Solenoid Valve’s Operation
Monday, July 23rd, 2018
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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
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
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
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
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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Tags: coil, compressed air, depositor, engineers, food manufacturing, jelly filling, magnetic field, pastry line, plunger, port, solenoid, solenoid valve, spool, switch, valve body, voltage source
Posted in Engineering and Science, Expert Witness, Forensic Engineering, Innovation and Intellectual Property, Personal Injury, Product Liability, Professional Malpractice | Comments Off on The Solenoid Valve’s Components
Monday, July 16th, 2018
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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 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
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
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
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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Tags: depositor, depositor diverter valve, engineering, linear motion, pastry production line, piston, pneumatic actuator, rotary motion, Scotch Yoke, slider, solenoid valve, yoke mechanism
Posted in Engineering and Science, Expert Witness, Forensic Engineering, Innovation and Intellectual Property, Personal Injury, Product Liability | Comments Off on The Depositor’s Scotch Yoke Motion
Monday, July 9th, 2018
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Last time, we learned how a pneumatic actuator was connected to a depositor’s positive displacement piston pump so that it could extract jelly filling from a hopper, and deposit it through a nozzle onto a passing pastry. The pneumatic actuator imparted linear motion to the pump during this process. Since the pistons in the actuator and pump both move in a straight line, it was very easy and straightforward to connect the actuator to the pump.
For the depositing process to work, we must have an additional actuator to rotate the diverter valve as the pump operates. The valve changes the flow path of the jelly between the hopper and the nozzle. More specifically, the valve must rotate clockwise to create a flow path between the hopper and the pump while the pump extracts jelly from the hopper.
The Diverter Valve Rotated Clockwise
When the pump is full of jelly, the diverter valve must rotate counter-clockwise to create a flow path between the pump and the nozzle. This path allows the pump to empty its contents trough the nozzle.
The Diverter Valve Rotated Counter-Clockwise
Although the diverter valve’s motion is rotary, it can be operated with the linear motion of a pneumatic actuator. To convert the linear motion of the actuator to the rotary motion needed to operate the valve, we can employ a device known to engineers as a Scotch Yoke.
The Depositor’s Scotch Yoke
In the Scotch Yoke, the pneumatic actuator’s piston rod is connected to a slider. As the piston moves back and forth in the pneumatic actuator, the slider is free to move back and forth along a fixed guide rod. A pin is located on the slider. The pin loosely engages a slot in the yoke mechanism. As the slider moves, the pin can move freely in the slot. The yoke mechanism is rigidly attached to the rotating diverter valve shaft.
Next time, we’ll look at the rotary motion of the Scotch Yoke as the pneumatic actuator piston moves to the right and then to the left during the jelly depositing process.
Copyright 2018 – Philip J. O’Keefe, PE
Engineering Expert Witness Blog
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Tags: depositor, diverter valve, engineering, guide rod, hopper, jelly filling, linear motion, nozzle, piston, piston rod, pneumatic actuator, positive displacement pump, rotary motion, Scotch Yoke, slider, yoke mechanism
Posted in Engineering and Science, Expert Witness, Forensic Engineering, Innovation and Intellectual Property, Personal Injury, Product Liability | Comments Off on The Depositor’s Scotch Yoke
Monday, July 2nd, 2018
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Last time we learned how pneumatic actuators impart linear motion to machines. Now, let’s see how the pneumatic actuator is connected to the depositor’s pump. The connection imparts linear motion to the pump so it draws in jelly filling from the supply hopper and sends it streaming out of the nozzle onto a passing pastry.
On the depositor, the pneumatic actuator’s piston rod is connected to the pump’s piston. As such, the pistons in the actuator and pump move together. When compressed air is admitted to the right side of the pneumatic actuator, the pistons in actuator and pump move to the left. As the pump’s piston moves to the left, a vacuum is formed in the pump. This vacuum sucks the jelly out of the hopper, through the diverter valve, and into the pump as shown below.
The Depositor’s Pneumatically Actuated Pump
Once the pump is full of jelly, compressed air is admitted to the left side of the actuator piston. The pistons in actuator and pump move to the right as the compressed air expands and presses against the piston in the actuator. As the pump’s piston moves to the right, pressure builds up on the jelly in the pump. The pressure empties the jelly from the pump. The jelly is forced from the pump, back through the diverter valve, and it streams out of the nozzle as shown below.
The Depositor’s Pneumatic Actuator Empties the Pump
For the pumping process to take place, the diverter valve must be rotated to first allow jelly to flow from the hopper. The diverter valve must be rotated again to allow jelly to flow through the nozzle. Next time, we’ll see how a pneumatic actuator is attached to a mechanical linkage that rotates the diverter valve.
Copyright 2018 – Philip J. O’Keefe, PE
Engineering Expert Witness Blog
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Tags: compressed air, depositor, jelly filling, linear motion, pastry, piston, piston rod, pneumatic actuator, pump, pump vacuum
Posted in Engineering and Science, Expert Witness, Forensic Engineering, Innovation and Intellectual Property, Personal Injury, Product Liability | Comments Off on The Depositor’s Pneumatically Actuated Pump
