Standard Grade Technological Studies

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Standard Grade Technological Studies

• OR control

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OR control

• Sometimes we need to control a pneumatic circuit
  from more than one position
• To do this we use or control.
• Although simple, these circuits require another
  component called a shuttle valve.

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Shuttle Valve

• A shuttle valve is used to change the direction
  of air in a circuit.
• It has a small ball inside that gets blown from
  side to side.
• The symbol for a shuttle valve is shown.

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Shuttle Valve

• A picture of the inside of the shuttle valve is
  shown below.

• When air is supplied from valve A.
• The ball gets blown across.
• Air is directed towards the cylinder.

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Shuttle Valve

• When air is supplied from valve B.
• The ball gets blown across.
• Air is directed towards the cylinder.

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OR control

• OR control involves connecting 3/2 valves in
  parallel.
• This means that pressing either valve will
  outstroke the cylinder.
• Below is a typical OR control circuit

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OR control

• The operation of an OR control circuit can be
  summarised in a truth table.

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Assignment 10
1. Part of a production line involves a quality
check. If goods are found to be faulty then they
are pushed of the conveyor by a single acting
cylinder.
Two people are employed to make sure that no
faulty good leave the factory. They each operate
the cylinder by pressing a button.
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Assignment 10

• Design a circuit that will solve the problem.
• Using a computer simulation, build and test your
  solution.
• Construct your circuit using pneumatic
  components.
• Explain how the circuit works.
• Some one has suggested changing the shuttle valve
  to a T-piece. Why is this not a good idea?
• (You may want to build this circuit to
  investigate)

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Assignment 10
2. A bus door is operated by pneumatics. The
door is opened by a single acting cylinder and is
controlled by a 3/2 valve. In an emergency,
there should be a second valve that allows
passengers to open the doors.
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Assignment 10

• Design a circuit to solve the problem with the
  bus doors.
• Using a computer simulation, build and test your
  solution.
• Construct your circuit using pneumatic
  components.
• Explain how your circuit works.
• Explain your choice of actuators.