1. Created By : Majid Iqbal
INSTITUTE : Construction Technology
Training institute Islamabad
TECHNOLOGY: Mechanical with
specialization in Construction Machinery
CONTACT : +923005524644

2. In the name of ALLAH, the
Beneficent and the Merciful

3. Hydraulic System
Chapter : 04
CONTROL VALVES

4. Question must be asked at theQuestion must be asked at the
end of presentationend of presentation

5. Control
valve
Pressure control valve
Flow control
valve
Directional control
valve

6. Pressure Regulating ValvePressure Regulating Valve
Pressure Regulating valve serves to adjust
the pressure in the circuit.

7. SAFETY VALVESAFETY VALVE
Safety is actuated only when pressure in
circuit increases excessively high
unexpectedly.
SYMBOL

8. Types of pressure
control valve

9. Kinds of relief valveKinds of relief valve
Relief
valve
Pilot type
Ball type
Spool type
Poppet type
Piston type
Differential pressure
type
Single stage
Two stage
Direct acting
type

10. Poppet type valve
PARTS

11. OPERATIONOPERATION
Valve will close
when Pressure is low.
Valve is open as
soon as the pressure
become high.

12. PISTON TYPE VALVE

13. OPERATIONOPERATION
Pressure is low to
overcome the spring
thrust.
When pressure
increases piston will
push the valve to
open exhaust port

14. Pilot operated valve

15. Operation At Low PressureOperation At Low Pressure
 Pilot valve will be close
at low pressure.
 It will block the oil flow
to balancing port.
 Main valve will not
actuate because of equal
pressure on both sides.

16. Operation At High PressureOperation At High Pressure
 Pilot valve will be open
at high pressure.
 Oil will flow to
balancing port and
creates a pressure
difference at both side
of main valve
 In this way Main Valve
will open the main port

17. A relief valve is actuated only when the
Pressure in any part of circuit increases
unexpectedly to an excessively high Value

18. Adjustment of set
pressure
The spring tension can be reduced by increasing
the number of shims for lower set pressure.
To increase the spring tension, number of
shims used should be reduced to increase set
pressure.

20. Troubles and corrective measures
 weak spring
 Loosening of
adjusting screw
Troubles

21. Corrective measures
 Set pressure can be
restored by removing
the shims.
 If spring is too weak to
give desired set
pressure, spring should
replace.
 If the adjusting screw is
loosened, it should
retightened to restore
desire set pressure.

23.  Directional control valves are used to
direct oil into separate circuits of a
hydraulic system.
 Directional Control Valves provide
links between various parts of the
hydraulic system, by connecting of
disconnecting and or changing the oil
flow direction.
Directional control valve
INTRODUCTION

24. HOLD LOWER RAISE

25. Control Valve:-
The directional control
valve determines the
path that fluid takes
through the system.
Direction control valve

26. FUNCTION OF CONTROL
VALVE
 Move the spool to left-hand position and this closes the right
side outlet port by spool land. now inlet port is connected to left
side outlet port.
 Move the spool to right hand position, this closes left side outlet
port by spool land. this connects inlet port to right side outlet port.

28. Designation:
The number of ports and the
number of valve positions that a DCV
has will be the basic to describe the
type of valve designation.
DCV DESIGNATION

31.  Hold a small amount of oil for lubrication
between body and spool.
 Assists with sealing.
 Retains small particles of contamination.
What is the function of Grooves?
What is the function of Metering
Notches?
Minimizes the possibility of
hydraulic lock up.
Better control of flow rates with
fine operation and cushioning.

32. Spools
Grooves Metering Notches

33. Graphic Symbols:Graphic Symbols:
5. Control Valve, hand actuated
This is an OLSS valve.
Control valve has three
positions:
 Hold.
 Tilt.
 Dump.
The check valve is to stop work
equipment from dropping
when the spool is just
opening.
5

34. FLOW CONTROLVALVE
Flow control valve serves to restrict the
flow of fluid.
SYMBOL :

35. Operation at Forward FlowOperation at Forward Flow
 When the oil is flowing in Direction indicated
by arrow, valve opens allowing the oil to flow
through center port and surrounding.

36. Operation at Reverse FlowOperation at Reverse Flow
 When the oil is flowing indicated by blue arrow,
Valve closes allowing oil to flow through center
port only.

37. APPLICATIONS
USED IN FORKLIFT TRUCKS

38. Oil should be fed into cylinder to lift the forks.The more oil is fed, the more the
forks lifting speed.
When forks lower under the own weight, causing oil in cylinder to flow back to
oil tank very rapidly.
To prevent the danger of rapidly lowering forks, oil must be restricted by letting
it go through a smaller port to slow the lowering forks.

39. When raising forks
When lowering forks

40. CHECK AND MAKEUP VALVES
Check valve is used in a hydraulic circuit to constitute the one-way
passage of oil and block the opposite direction passage.
The makeup valve is used to make up the lack of oil so as to prevent the
vacuum from being produced in the cylinder..it also prevents reverse flow
of oil from cylinder to tank.
Check valve and makeup valve has same construction but has different
functions.

41. SYMBOLS

42. APPLICATION
BUILT IN A VALVE SPOOL OF
HYDRAULIC CONTROL VALVE

43.  Oil is fed from the pump, the check valve opens, allowing the oil
to flow into cylinder to raise the bucket.
 When stopping the oil feed or abnormal loading on bucket will
give a possibility of oil from cylinder to flow back under bucket
load. then check valve closes to prevent reversal of flow and
preventing bucket from lowering.

44. TENDEM CONNECTION
Construction simpler and compact.
Smaller size comparatively.
Simultaneous operation is impossible.

46. SERIES CONNECTION
 Simultaneous operation is possible. however, its becomes
impossible when first cylinder piston reaches the end
stroke.
 Two spools equally divide oil pressure, it reduces output
force of each actuator to half of what it can display when
operated independently.

48. PARALLEL CONNECTION
 All spools can be operated simultaneously and
independently.
 During simultaneous operation, the cylinder with
lighter load will operate earlier and at a faster speed. it
is necessary to keep loads roughly equal.

50. RESTRICTION
 It is a device for reducing
flow cross-section and
provides resistance in fluid
passage.
 It can be provided by chock
and orifice restrictions.

51. ORIFICE
 It is a small hole in oil passage.
 The orifice length is shorter
than its cross-sectional area.
 The pressure after orifice is
lower than before it.
 Pressure difference is increased
when flow increases and when
orifice becomes smaller.

53. CHOKE
It is a throttle device which is long as compared
with its internal cross-sectional area.
It can act both as a orifice and as a choke.
If area increases, it will behave as a orifice and if
area decreases, it will behave as a choke.

55. VALVE CHATTERINGVALVE CHATTERING

57. THANK YOU FOR YOUR KINDTHANK YOU FOR YOUR KIND
ATTENTION!ATTENTION!