Posts Tagged ‘jelly filling’

The Depositor’s Scotch Yoke

Monday, July 9th, 2018

    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

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

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

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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The Depositor’s Pneumatically Actuated Pump

Monday, July 2nd, 2018

    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 Pneumatic Actuator Empties the Pump

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

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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