Standard Grade Technological Studies

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Standard Grade Technological Studies

• Flow control valves

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Flow control valves

• Normally pneumatic pistons move very quickly.
• This can be dangerous.
• To slow the speed of a piston down we can use a
  flow control valve.
• There are generally two types available to us.

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The Restrictor

• Often referred to as a throttle valve.
• Works by reducing the amount of space the air can
  flow through.
• Can be adjusted by turning the small screw on top
  of the valve.
• The symbol for a restrictor is shown.

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The Restrictor

• The restrictor slows the flow of air in both
  directions.
• In the circuit shown, a restrictor is used to
  slow the speed of the single acting cylinder.

• The problem with this type of restrictor is that
  it slows the piston in both directions.

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The Unidirectional Restrictor

• This restrictor slows the flow of air in one
  direction only.
• The symbol for a unidirectional restrictor is as
  follows...

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The Unidirectional Restrictor

• Air flows into port 1...

• Some of the air takes the bypass route...

• This blows a small ball against a valve and
  blocks this path...

• The air is forced through the restriction,
  slowing down the airflow.

By-pass
Air flow
Restriction
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The Unidirectional Restrictor

• Air flows into port 2...

• Again, some of the air takes the bypass route...

• The ball is blown away from the valve...

• The air is flows through the bypass unrestricted.

By-pass
Air flow
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Restrictor circuits

• Unidirectional restrictors are more useful to us.
• We must ensure that they are inserted into a
  circuit in the correct orientation.
• We always restrict the exhaust air coming from
  the cylinder.
• This makes the piston operate much more smoothly.

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Assignment 8

• 1. Back to the car park barrier. Some one
  suggests further modifying the circuit...

• Build and test the circuit shown to raise the
  barrier slowly
• Describe how the system operates.
• Why do we restrict the exhaust air when slowing
  down the speed of the piston?

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Assignment 8
2. For safety reasons, the entrance door to a
store room must open and close slowly. A double
acting cylinder is used to slide the door.
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Assignment 8
2. The circuit diagram for the door mechanism is
shown, with some of the piping missing.

• Copy and complete the circuit diagram.
• Build and test the door opening circuit.
• Describe how the circuit operates and why two
  restrictors are needed in this circuit.

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Assignment 8
3. Part of a manufacturing process involves
dipping components in a chemical solution to
prepare them before they are painted.
A double acting cylinder controls the
process. For safety reasons the cylinder must
outstroke and instroke slowly.
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Assignment 8

• Design a circuit that will solve this problem.
• Using computer simulation, build and test your
  solution.
• Construct your circuit using the pneumatic
  components.
• Describe how your circuit operates to solve the
  problem.
• Why is it important that the cylinder operates
  slowly in both directions?