The document discusses directional control valves and their components. It describes common types of directional valves like spool valves, poppet valves, and unidirectional valves. It also discusses solenoids and pneumatic and hydraulic systems that use directional control valves to direct fluid flow. Standard symbols for different valve types are presented along with examples of their use in diagrams.

1. ICE 3015: CONTROL SYSTEM
COMPONENTS
Class 18: Directional Valves and
Symbols
Dr. S. Meenatchisundaram
Email: meenasundar@gmail.com
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

2. Directional Control Valves:
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018
• Pneumatic and hydraulic systems use directional control valves to
direct the flow of fluid through a system
• Its ON/OFF devices either completely open or closed
• They might be activated to switch the fluid flow direction by means
of mechanical, electrical or fluid pressure signal
Common Types:
1. Spool Valve
2. Rotary Spool Valve
3. Poppet Valve
4. Unidirectional Valve

3. Spool Valves:
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018
• Spool Valve: Move horizontally within the valve body to control flow
• Rotary Spool Valve: when rotates opens and closes ports

4. Poppet Valves:
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018
• This valve is normally in closed
condition.
• In this valve, balls, discs or
cones are used in conjunction
with valve seats to control the
flow.
• When the push-button is
depressed, the ball is pushed
out of its seat and flow occurs
as a result of port 1 being
connected to port 2.

5. Unidirectional Valves:
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018
• Free flow can only occur in one direction through the valve, flow in
the other direction is blocked by spring.

6. Solenoids:
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018
• A solenoid is a coil wound into a tightly packed helix.
• In physics, the term solenoid refers to a long, thin loop of wire, and
wrapped around a metallic core.
• Which produces a magnetic field when an electric current is passed
through it.

7. Valve Symbols:
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018
• The valve symbol consists of square for each of its switching
positions.
• Thus for the shown poppet valve there are two positions, one with
the button not pressed and one with it pressed.
• Thus two positions valve will have two squares, a three positions
valve have three squares.

8. Valve Symbols:
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

9. Valve Symbols:
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018
• 1 (or P) for pressure supply
• 3 (or T) for hydraulic return port
• 3 or 5 (or R or S) for pneumatic exhaust ports
• 2 or 5 (B or A) for output ports

10. Solenoid operated spool valve:
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

11. Solenoid operated spool valve:
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018
• Figure in last slide shows the symbol for a 3/2 valve, the connection
is shown for initial state
• i.e. 1(P) is connected to 2(A); 3(R) is closed.
• When the solenoid is activated, it gives the state indicated by the
symbols used in the square to which it is attached,
• i.e 1(P) closed and 2(A) connected to 3(R).
• When current through the solenoid ceases the spring pushes the
valve back to its initial position.

12. Working of Hydraulic Actuators:
• Α directional control valve controls the direction of oil flow in the
system and, therefore, the direction of motion of the cylinder piston.
• The valve has four ports, labelled Ρ, Τ, Α, and Β. Ρ and Τ stand for
pressure and tank (or reservoir), and Α and Β are output ports. The
valve can be operated in three different positions.
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

13. Working of Hydraulic Actuators:
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2015
• The oil from the pump flows through path Ρ-Α of the valve to the
upper end of the cylinder.
• The oil pushes the piston downward, which lowers the attached load.
At the same time, the oil at the lower end of the cylinder flows back to
the reservoir through path Β-Τ of the directional control valve.

14. Working of Hydraulic Actuators:
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2015
• When the directional control valve lever is released, the valve
automatically returns to the center (neutral) position.
• In this position, all four ports are blocked and oil cannot escape from
either side of the cylinder. This stops the movement of the piston and
causes oil to flow from the pump back to the reservoir through the
pressure relief valve.

15. Rotary Hydraulic Actuators:
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2015

16. Hydraulic & pneumatic actuators: Cylinders
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2015

17. References:
• http://web.itu.edu.tr/yalcinme/files/courses/MMG/ch5%20Hydraulic
%20and%20pneumatic%20actuators.pdf
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018