The document presents an overview of various types of directional control valves (DCVs) including solenoid actuated and pilot controlled check valves, detailing their functions, operations, and key components. It explains the differences between solenoid valves and proportional valves, emphasizing the role of current signals in their operation, as well as the importance of servo valves for precise control in hydraulic systems. Additionally, it covers the mechanics of these valves, providing insights into their construction, control mechanisms, and common applications in hydraulics.

2. Presented By :
SRICHANDAN SUBUDHI
GET, CSP MILL – E & A
Bhushan Power And Steel Ltd.

3. After this presentation you will be knowing :
•
What are DCVs, its type and their uses
•
About Check Valves and pilot controlled check
valves
•
What are solenoid actuated valves and their
operation
•
What are proportional solenoid valves and their
operation
•
Servo Valve Operation
•
Servo Valve Connector

4. DIRECTIONAL CONTROL VALVE
•
The primary function of a DC valve is to direct
or prevent fluid flow to specific piping or system
actuator.
•
These valves usually consists of spool inside it
which is electrically/hydraulically controlled.
•
There are two fundamental positions of these
valves :
1. Working Position
2. Normal Position

5. •
According to no. of valve ports and spool position
DC valve can be categorized into following :
1.
2.
3.
4.
2-way,
3-way,
4-way,
4-way,
2-position
2-position
2-position
3-position and many more…

6. Common Abbreviation used in Hydraulics
P = Pressure line
T = Tank Line
A,B = System Actuator line
X = Pilot Line
Y = Drain Line

7. Spool Position

8. 2 - Way, 2 – Position DC Valve

9. 3 – Way, 2 - Position DC Valve

10. 4 – Way, 2 – Position DC Valve

11. 4 – Way, 3 – Position DC Valve

12. •
Electrically actuated DC Valves are actuated
by means of solenoid. They can be single/double
solenoid actuated. When these solenoids are
energized the DC valves are shifted to Working
position.
•
Along with solenoid, there are spring
actuators which are used to shift the spool of a DC
valve to normal position when the solenoid is deenergized.

13. Single solenoid, 2 – position,
Spring Offset

14. Double Solenoid, 2 - Position

15. Double Solenoid, 3 – Position,
Spring Centre

16. Common Hydraulic Symbols
1. Continuous line – Flow line
2. Dashed line – Pilot , drain
3. Spring
4.
Flow Restriction
5.
Single Acting Cylinder
6.
Double Acting Cylinder
7.
2-way, 2-position DC valve (NC)
8.
2-way, 2-position DC valve (NO)
9.
3-way, 2-Position DC valve (NO)
10. 3-way, 2-Position DC valve (NC)

17. 11. 4-Way, 2-position DC valve
12. 4-way, 3-position DC valve
13. Solenoid actuated
14. Hydraulic Actuated
15. Check Valve
16. Pilot operated Check Valve
17. Pressure Relief valve

18. SOLENOID ACTUATED DC
VALVES
It is an electro-mechanical device that take
electrical energy and produces a linear force by the use
of magnetism. It is basically a winding of wire around a
metal core.

19. When the solenoid is energized, the air gap is
closed quickly and a force is developed in the direction
of the valve spool.

20. SOLENOID CONTROLLED, PILOT-OPERATED
DCV
Although a valve could be shifted directly by the
force of a solenoid, large flow DCVs are most often
shifted using fluid at system pressure. Larger flow
valves demand larger shifting forces and it is no longer
practical to use a solenoid there.

21. CHECK VALVE
•
A check valve, non-return valve or one-way
valve is a valve that normally allows fluid to flow
through it in only one direction.
•
Check valves are two-port valves, meaning they
have two openings in the body, one for fluid to enter
and the other for fluid to leave.
•
An important concept in check valves is the
cracking pressure which is the minimum upstream
pressure at which the valve will operate.

23. PILOT OPERATED CHECK VALVE
•
This type of check valves are remotely operated
through any one of the directional valves.
•
This is controlled by a pilot pressure line
which is indeed controlled by a directional control
valve.

24. X : Pilot line
A : I/P line to the check valve
B : O/P line from the check valve
•
The main application of check valves is to hold
the pressure of a load and for safety purposes.

25. PROPORTIONAL VALVE
•
The proportional DCV is actuated by means of
an electrical control signal. The control signal
influences the flow rate and flow direction.
•
It is exactly the same as the solenoid valve
except that solenoid valve acts as ON/OFF switch
whereas this proportional solenoid valve can achieve
each and every point in between thus varying the flow
rate.
•
Different flow rate is achieved by varying the i/p
current signal.

26. DIFFERENCE BETWEEN SOLENOID AND
PROPORTIONAL VALVE
1. Solenoid valve
Normally close position

27. Fully Open position

28. 2. Proportional Valve
Normally close position

29. Intermediate Position ( 30% Open )

30. Intermediate Position ( 60% Open )

31. Fully Open Position

32. • The difference between a solenoid and a proportional
solenoid valve is in the construction of their spool.

33. 
How Signal Flows in It ?
i. Electrical Voltage ( -10V to +10V ) acts upon
an amplifier.
ii. The amplifier converts voltage into current
signal.
iii. The current acts upon the proportional
solenoid, which actuates the valve.

35. 
So, In general a proportional valve is a
combination of both flow control valve and
directional control valve.

36. SERVO VALVE OPERATION
•
A hydraulic servo valve is a servo (spool) with a
flapper nozzle system used to position the servo. The
term electro-hydraulic servo valve is often used because
servo valves are controlled through an electrical signal.
•
The primary components in a servo valve are a
torque motor, flapper nozzle , and spool.

39. •
The Servo valve has a hydraulic pressure inlet and an
electrical input for the torque motor. The input current controls
the flapper position. The flapper position controls the pressure in
rod side or piston side of the cylinder. So, a current (+ or -) will
position the flapper, leading to a delta pressure on the servo,
which cause the servo to move in one direction or the other.
Movement of the servo ports hydraulic pressure to one side of the
actuator or the other, while porting the opposite side of the
actuator to return.
•
Flapper position is controlled by the electromagnetic torque
motor. A torque motor consists of two permanent magnets with a
coil winding attached to a magnetically permeable armature. The
armature is part of the flapper piece. When a current is applied to
the coils, magnetic flux acting on the ends of the armature is
developed. The direction of the magnetic flux (force) depends on
the sign (direction) of the current.

40. •
The magnetic flux will cause the armature tips to be
attracted to the ends of the permanent magnets (current direction
determines which magnetic pole is attracting and which one is
repelling). This magnetic force creates an applied torque on the
flapper assembly, which is proportional to applied current.
•
As the applied current is increased, the armature and
flapper will rotate. As the flapper moves closer to one nozzle, the
flow area through this nozzle is decreased while the flow area
through the other nozzle increases.
•
In the above the figure the flapper nozzle consists of the
flapper, two inlet orifices (O1 and O2), two outlet nozzles (n1 and n2),
nozzle backpressure nozzle (n3) and usually a feedback spring. As
described above, the torque motor positions the flapper, which in
turns controls the flow through the nozzles. When the flapper is in
the neutral position, the nozzle flow areas are equal and the
pressures Pn1 and Pn2 are equal. When the flow areas and inlet
nozzle pressures are equal, the flow forces through each nozzle keep
the flapper centered in the neutral position.

41. •
As the flapper moves towards one of the nozzles, the outlet
flow area is reduced for this nozzle. Outlet flow area increases for
the other nozzle. For example, looking at Figure let the flapper
move towards the n1 nozzle. This will reduce the outlet flow area
and the pressure Pn1 will increase. At the same time, the outlet
flow area at the n2 nozzle will increase and the pressure P n2 will
decrease. A delta pressure ΔP = Pn1 – Pn2 will occur across the pilot
spool piston and the pilot spool will displace to the right. High
pressure fluid will then flow to the P A actuator chamber while the
PB actuator chamber is ported to return.

42. •
Servo valves are normally used when accurate position
and force control is required.
•
The main advantage of a servo valve is that a low power
electrical signal can be used to accurately position an actuator
or motor.
•
The disadvantage is complexity and cost which results
from a component consisting of many detail parts manufactured
to very tight tolerances. Therefore, servo valves should only be
used when accurate position (or rate) control is required.

43. SERVO VALVE CONNECTOR

44. PIN
FUNCTION
A
SUPPLY VOLTAGE
B
GROUND
C
ENABLE INPUT
VOLTAGE /
CURRENT RATING
D
COMMAND SIGNAL I/P
24 V DC
< 6.5 V DC DISABLED
-10 to +10 mA OR
4 – 20 mA
E
F
COMMAND SIGNAL O/P
G
P.E.
4 – 20 mA

45. SERVO CONNECTOR
X
Y
POTENTIOMETER
(4 – 20 mA)
24 v dc
A B C D E
G
CONNECTOR

46. In No Load Condition
When the wiper is at ‘X’ end :
Current across DE will be, 24/970 = 24 mA (Apprx. )
When the wiper is at ‘Y’ end :
Current across DE will be 0 mA.