Pneumatic Valves

1
Pneumatic Valves

• Lesson 4

2
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.

3
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.

4
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 relief and pressure regulation.
• Pressure relief valves are pressure limiting
  devices which keep the system pressure below a
  preset maximum.

5
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 atmosphere.

6
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.

7
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
  valve open.

8
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.

9
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
  equipment.

10
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

11
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.

12
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.

13
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.

14
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.

15
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.

16
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 of concern.

17
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
  pneumatic devices.

18
Directional Control Valves

• To control machine processes and to sense a
  manual or mechanical movement and initiate a
  signal.

19
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.

20
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.

21
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, mechanical, pneumatic and electric.
• Types of returns include
• Manual, Spring, pneumatic, and electric.
• A manual actuator is any actuating device which
  is controlled directly by the operator.

22
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
  information.

23
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

24
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.

25
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.