Pneumatic Valves
Lesson 4
1
Introduction
 Compressed
air and gases must be controlled to be
useful.
 One of the advantages of pneumatic systems is the
ease and precision with which the system can be
controlled.
 Valves are used to control the pressure of
compressed gases as well as the rate and direction
of flow.
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Introduction
 This
in turn controls the action of the device using
the compressed air or gas.
 Valves are used throughout industry to control
compressed air and gases that industry depends on.
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Pressure Control Valves
 Pressure
control valves are used to maintain a
preset pressure in the entire air system or in just
one part of the air system.
 Pressure control can be achieve through 2
methods:
 Pressure
 Pressure
relief and pressure regulation.
relief valves are pressure limiting devices
which keep the system pressure below a preset
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maximum.
Pressure Control Valves
 They
consist of a housing and a ball or poppet
which is held in position by a spring.
 This spring tension against the ball or poppet holds
it against a seat and prevents air flow through the
valve.
 As the pressure increases, it creates a force against
the ball until it overcomes the spring force and
pushes the ball from its seat.
 This allows the excess pressure to exhaust into the
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atmosphere.
Pressure Control Valves
 A pressure
relief valve should be designed into
every compressed air system
 This should be adjusted to prevent the system
pressure from exceeding the pressure ratings of the
components in the system.
 They are usually used in combination with a
pressure switch which turns the compressor on or
off.
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Pressure Control Valves
 The
pressure regulator is a valve that monitors the
air pressure downstream of it and automatically
opens and closes to maintain that pressure at a
preselected value.
 It consists of a housing, valve and valve stem, a
sensing diaphram, and an adjustment spring.
 The spring maintains force against the diaphram
which pushes against the valve stem and holds the
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valve open.
Pressure Control Valves
 This
allows air to flow through the regulator to
components located downstream.
 As pressure on the downstream side of the
regulator increases, it exerts force against sensing
diaphram.
 As the force increases it overcomes the spring
force and opposes the pressure it spring exerts
against the valve stem.
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Pressure Control Valves
 This
allows the valve to close.
 As downstream pressure decreases the force
against the diaphram diminishes and the spring
reopens the valve which allow air to flow again.
 Pressure regulators should be installed at the points
in the air distribution system where an air operated
device is used.
 This allows the air pressure to be adjusted to meet
the individual requirements of each piece of
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equipment.
Flow Control Valves
 Flow
control valves are used in a pneumatic
system to govern the rate at which air is allowed to
flow.
 They are available in 2 styles:
 Needle
valves and Flow controls
 Needle
valves control flow in both directions.
 Flow controls control flow in 1 direction
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Flow Control Valves
 The
needle valve consists of a tapered needle
which can be adjusted in relation to a fixed orifice
in the housing.
 Moving the needle away from the orifice created
less restriction and allows more flow while moving
the needle closer increases the restriction and
reduces the flow.
 Needle valves are used where the flow needs to be
controlled in both directions through the line. 11
Flow Control Valves
 The
flow control valve combines a needle valve
and a check valve in one housing.
 The needle valve controls the flow in one direction
and the check valve allows free flow in the other
direction.
 The most common application for a flow control
valve is to control the speeds of pneumatic
cylinders and motors.
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Directional Control Valves
 Directional
control valves are used to start, stop,
and direct the flow of air in a pneumatic system.
 By directing the flow of air, these valves control
the action of other pneumatic devices, such as
cylinders, motors, pumps, or other valves.
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Directional Control Valves
 Directional
control valves are constructed in a
variety of ways.
 The main types include ball valves, poppet valves,
and spool valves.
 Each of these valves have specific performance
characteristics that make them adaptable to
particular application.
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Directional Control Valves
 Ball
valves consist of a spherical element encased
in a housing.
 The element is rotated by means of a handle which
extends through the housing.
 As it rotates, passages machined in the ball
connect and disconnect various ports in the
housing to permit or interrupt air flow.
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Directional Control Valves
 Poppet
valves are composed of moving elements
called poppets, which seat against the valve
housing to prevent air flow, or lift from their seat
to allow flow.
 They are inherently a very high flow valve with
rapid response and low maintenance.
 They are often used to control the air supple where
high flow is required and in control circuits where
rapid response time and low maintenance are of16
concern.
Directional Control Valves
 Spool
Valves are the most versatile and extensively
used valve in pneumatic circuit.
 They consist of a cylinder spool which slides
through a cylindrical bore in a housing.
 Recessed areas of the spool connect ports to
provide passage through the valve while larger
areas of the spool seal off other ports.
 They are used to direct air flow for powering
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pneumatic devices.
Directional Control Valves
 To
control machine processes and to sense a
manual or mechanical movement and initiate a
signal.
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Functions of Directional Control
Valves
 Directional
control valves are classified as to the
way they function?
 The 3 main categories of directional control valves
are 2 way, 3 way, and 4 way.
 The 2 way directional control valve contains 2
working ports and 1 flow path between these ports.
 The valve has 2 operating positions and is
sometimes referred as a 2/2 valve.
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Functions of Directional Control
Valves
 The
3 way directional control valve contains 3
working ports and provides 2 flow paths.
 This valve also has operating positions and is
sometimes referred to as a 3/2 valve. (3 way, 2
position)
 4 way directional control valves contain either 4 or
5 working ports.
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Actuators & Returns
 Spool
valves can be actuated in a variety of ways
depending upon what the function of the valve is.
 Types of actuators include:
 Manual,
 Types
mechanical, pneumatic and electric.
of returns include:
 Manual,
 A manual
Spring, pneumatic, and electric.
actuator is any actuating device which is
controlled directly by the operator.
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Actuators & Returns
 It
is usually used to initiate start and stop signals to
the circuit.
 The common manual actuators are palm button,
push button, hand lever, foot pedal, and treadle.
 A mechanical actuator is any actuating device
triggered by another mechanical device.
 They are used to sense the location of a moving
member and initiate a signal to relay this
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information.
Actuators & Returns
 The
common mechanical actuators are roller cam
and cam stem.
 Pneumatic Actuators receive a signal from another
valve to shift the spool.
 These valves are normally used as a power valve
receiving their signals from smaller limit valves.
 They are available in pilot and bleed
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Actuators & Returns
 Electric
solenoid actuators all the combination of
electrical circuitry with pneumatic power devices.
 Electric switches send current to the solenoid to
open the valve which controls the power device.
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Actuators & Returns
 Returns
 Types
of returns vary with the actuator used and the
application.
 The common returns include:
 Manual, detent, spring, pilot, internal pilot, internal
differential pilot, external differential pilot, bleed, and
solenoid.
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