Standard Grade
Technological Studies
Flow control valves
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.
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.
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.
The Unidirectional
Restrictor
• This restrictor slows the flow of air in
one direction only.
• The symbol for a unidirectional restrictor
is as follows...
1
2
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
1
2
Restriction
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
1
2
Air flow
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.
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?
V alve A
V alve B
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.
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.
V alve A
V alve B
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.
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?