Hydraulics today has become a way of life as most applications have some form of system ingrained. This paper is an endevor to present the very basics of hydraulics and overcome its basic fear.

1. BASIC HYDRAULICS
A SYSTEM STUDY
PINAKI ROY

2. A TALK OVERVIEW
•
•
This talk has been designed to provide instruction on the concept
and operation of the basic components of the hydraulic system.
It also describes the various components of a typical hydraulic
system, their construction and functions, and their relationship to
each other. However to really appreciate & know about hydraulics
‘hands on’ experience, is a MUST.

3. Fluid Power System
• Fluid Power Systems are power
transmitting assemblies employing
pressurised liquid or gas to transmit
energy.
• Fluid power can be divided into two
basic disciplines
> Hydraulics – Employing pressurised
liquid
> Pneumatics - Employing
Compressed gas

4. What is Hydraulics?
• Hydraulics is derived from the Greek
word
- Hydor meaning Water
- Aulos meaning Pipe

5. Definition of Hydraulics
In simple language:
Confined liquids under pressure made to do work.
OR
Science of transmitting force / motion through
medium of confined liquid

6. HYDRAULICS DEFINED
FURTHER…
•
Fluid Mechanics is the physical science and technology of the static
and dynamic behavior of fluids.
Hydraulics is a topic in applied science and engineering dealing with
the mechanical properties of liquids. Fluid mechanics provides the
theoretical foundation for hydraulics, which focuses on the
engineering uses of fluid properties.

7. PASCAL’S LAW
Pascal Law – which is the basis for all
hydraulic systems, is named after the French
Scientist – Blaise Pascal, who established
the law.

8. Do you remember Pascal’s
Law?
•
•
It states that “ Pressure exerted anywhere in a confined
fluid is transmitted equally in all directions throughout the
fluid.
The basic idea behind all hydraulic system is based upon that
principle & can be simply stated as:
Force applied at one point is transmitted to another point
using an incompressible fluid.

9. PASCAL’S LAW
ILLUSTRATION

10. Working Principle of a Hydraulic
Press

11. Functions of Hydraulic Oil
• It transmits power.
• It lubricates moving parts
• It seals clearances
between moving parts
• It dissipates heat

12. Advantages of oil in Hydraulics
• Variable speed
• Reversible
•
•
•
•
•
•
•
•
•
•
need
direction.
Over load protection
overSmall package
:
power
Can be stalled
:
Simple design
Self lubricated
Flexible
location
components.
Smooth
Acts as coolant
Acts as seal
mating parts.
Noise free
:
:
:
: Possible to control speed through valve.
: Instant reverse motion is possible. No
to stop the system to change
: Protected through relief valve from
loading.
Components are smaller than other
transmitting system.
Not possible on direct drive system from
Electric motor / Diesel engine.
Pre-engineered components available.
Hydraulic oil lubricates the parts.
Flexible hoses virtually eliminate the
problem of the hydraulic
: Incompressible, no vibration.
: It dissipates heat / cools the component,
; It seals clearances between two
: No noise.

13. Force that is applied at one point is
transmitted to another point using an
incompressible fluid
• In this drawing, two pistons (green) fit into two glass
cylinders filled with oil (blue) and connected to one
another with an oil-filled pipe. If you apply a downward
force to one piston (the left one in this drawing), then the
force is transmitted to the second piston through the oil
in the pipe

14. •
Force the left is 2 inches in diameter (1-inch radius),
Multiplication
Assume that the piston on
while the piston on the right is 6 inches in diameter (3-inch radius). The area
of the two pistons is Pi * r2 . The area of the left piston is therefore 3.14,
while the area of the piston on the right is 28.26. The piston on the right is 9
times larger than the piston on the left. What that means is that any force
applied to the left-hand piston will appear 9 times greater on the right-hand
piston. So if you apply a 100-pound downward force to the left piston, a 900pound upward force will appear on the right

15. Hydraulic System
• Reservoir
• Filter
• Hydraulic Pump
• Directional Control Valve
• Pressure Control Valve

16. Reservoir- Properties
First a tank is needed to store the hydraulic oil
Tank / Reservoir
Storing oil
Compensates difference in volume
when actuators are used
It dissipates heat
It allows foreign particles to settle
down
Baffle separates inlet line with the
return line and allows the air
bubbles to escape

17. More Properties of Reservoirs
• It allows condensed water to settle at the
bottom of the tank
• Breather on the top of the tank allows to
maintain atmospheric pressure and avoid
creation of vacuum
• Sight glass will indicate the level of the oil.
Mercury bulb indicates the oil temperature
• Oil filling inlet will have a filter for avoiding
contamination.

18. PUMPS
• Hydraulic Pump is the most important
component in the hydraulic system.
• Function of the Hydraulic Pump is to convert
Mechanical Energy to Hydraulic Energy
• Hydraulic Pump are classified in two
categories:
- Hydro-dynamic
- Hydro-static

19. Pump
Now we need a pump to create flow
Tank
Pump
Two types of hydraulic pumps are
most commonly used:
- Rotary Pumps
- Reciprocating Pumps

20. ROTARY & RECIPROCATING
TYPES
• Common Pumps in Rotary type are:
- Gear Pumps
- Vane Pumps
• Common Pumps in Reciprocating type
•
are:
Axial Piston Pump
Radial Piston Pump

21. ACTUATORS
• An actuator is a mechanical device for
moving or controlling a mechanism or
system. An actuator typically is a
mechanical device that takes energy &
converts it to a desirable form for usage or
application.
Actuator
Tank
Pump

22. ACTUATORS Contd…
• There are mainly two types of
Actuators:
- Linear actuators (single acting
cylinders, double acting cylinders)
- Rotary actuators (vane motors,
gear motors, piston motors etc.)

23. Types of Valves
• There are three main types of
Valves:
- Pressure Control Valves (relief
valves, pressure regulating valve,
pressure reducing valve etc.)
- Directional Control Valves (check
valve, axial spool valve, ball valve
etc.)
- Flow Control Valves (needle valve,
throttle check valve etc.)

24. Hydraulic System – some applications of
the basic components Actuator
Hoses to
connect the
components
Piston reverse
movement is not
possible
We need a direction
control valve to change
the direction of flow as
per requirement
Pump
Tank

25. Hydraulic System
Actuator
There are mainly two
design principles for
valves
Direction
Control Valve
- Spool valves
- Poppet valves
Pump
Tank

26. Hydraulic System
Actuator
Direction
Control Valve
The control valve is at
neutral position
Pump
Tank

27. Hydraulic System
Actuator
Now the control valve
is shifted to left
Direction
Control Valve
Pump
Tank

28. Hydraulic System
Actuator
Direction
Control Valve
To change the piston
movement in opposite
direction the control
valve is now shifted to
right
Pump
Tank

29. Hydraulic System
Actuator
Is it a complete circuit ?
OR
We need some thing more
Direction
Control Valve
Pump
Tank

30. Hydraulic System
Actuator
Piston at end
-No room to
move
Pressure
increases
Direction
Control Valve
yes
We need some thing more
Pump
Tank
We need to
control the
system pressure

31. Hydraulic System
Actuator
Direction
Control Valve
Pressure
relief valve
Pump
Tank

32. Hydraulic System
Actuator
Direction
Control Valve
Pressure
relief valve
Pump
Tank

33. Hydraulic System
Actuator
Direction
Control Valve
Pressure
relief valve
Stops pressure increasing
beyond the preset value
Pump
Tank

34. Hydraulic System
Actuator
Now we have a system
which can work
But is this system protected
from dirt ?
Direction
Control Valve
Pressure
relief valve
Pump
Tank

35. Hydraulic System
Actuator
We need to protect the system
from dirt by installing a FILTER
in the system
Direction
Control Valve
Pressure
relief valve
We have a system now which
can work safely
Pump
Filter
Tank

36. FILTERS
• There are basically three
types of Filters
- Suction line filters
- Pressure line filters
- Return line filters

37. Why is filtration necessary?
• Impurities in the Hydraulic
•
system affect the components
of the hydraulic system and
shorten their service life.
Reduction in service life of the
components occurs in two
ways:
- Wear and Tear
- Breakdown of component
Filters are used to remove the
smallest insoluble particles
and keep the hydraulic system
clean

38. Hydraulic System
Now we know :
Actuator
•
•
Pump creates flow
•
Resistance creates pressure
•
Actuators perform the work
•
Hoses transmit the oil
•
D.C. Valves change direction of
oil flow
•
Pressure
relief valve
Filter cleans the system
•
Direction
Control Valve
A Reservoir contains oil
Relief valves control the
maximum system pressure.
Pump
Filter
Tank

39. Hydraulic System
Actuator
Few more facts:
•
•
Direction
Control Valve
Pressure
relief valve
Pump
Filter
Tank
Pressure increases the system
capacity
Flow increases the system
speed

40. This Excavator weighs over 28 tons, but
has swift movements. The bucket can
effortlessly scoop out more than a cubic
meter of rock weighing about 2.0T

41. Transmission of Hydraulic
Power is connected to a pair of pumps that can
• The engine
generate 140 gallons per minute at 4,500 psi. You can
see from the picture that the arm has a pair of pistons
working in unison at the "shoulder" -- one at the "elbow"
and then one to rotate the bucket.

42. Transmission of Hydraulic
Power
• These pistons, along with the two track motors and the
rotating motor, are all controlled by two joy sticks and
four pedals in the cab. These controls send electrical
signals to an electrically-operated valve block located
next to the pump.

43. Transmission of Hydraulic
Power
• From the valve block, high-pressure hydraulic lines make
their way to the cylinders & they get activated whereby
the bucket can be moved as desired from the cabin with
the touch of a button.

44. Some Basic Calculations
• A 4-inch piston has an area of 12.56 square inches. If the pump generates a
•
maximum pressure of 3,000 pounds per square inch (psi), the total pressure
available is 37,680 pounds, or about 20 tons.
Another thing you can determine is the cycle time of the piston. To move a
4-inch-diameter piston 24 inches, you need 3.14 * 22 * 24 = 301 cubic
inches of oil. A gallon of oil is about 231 cubic inches, so you have to pump
almost 1.5 gallons of oil to move the piston 24 inches in one direction.
These form the basic criteria while selecting the hydraulic pump. For
example the actual engine, pump & sump details for this excavator is:
Engine
Cummins 6CT 8.3-C
8,270 cubic centimeters
340 horsepower at 1,900 rpm
Pump
Maximum pressure: 5,000 psi (4,500 psi)
Oil flow: 2x270 liters per minute
Capacities
Fuel: 530 liters
Engine oil: 22 liters
Hydraulic oil: 320 liters

45. DUMP TRUCKS or TIPPERS
• DUMPERS WITH TELESCOPIC
CYLINDERS & HYDRAULIC STEERING

46. What exactly is "full
hydraulic steering?"
• The expression refers to any steering system
configurations where a vehicle is steered solely by
means of a hydraulic circuit comprising, as a minimum, a
pump, lines, fluid, valve, and cylinder (actuator). that is to
say, the vehicle is steered (usually via the front wheels)
purely by a hydraulically powered steering cylinder. This
is an important distinction from "hydraulically assisted"
steering, where hydraulic power serves only to assist a
mechanical steering system (as is the case with the
hydraulically assisted power steering on virtually every
light car / truck on the road today). It indicates that the
vehicle is steered ONLY by hydraulics, with no other
system (mechanical linkage) in place.

47. Why use hydrostatic steering?
•
Because there are a number of distinct advantages :
•
Power - depending on system design parameters (flow, pressure, cylinder size, etc.)
hydro steering can develop steering force FAR in excess of any other mechanical,
electrical, or hydraulically boosted system. This is a must for massive construction
equipment. It is also extremely advantageous to 4x4s with big tires, locker
differentials, low tire pressures, the must negotiate and be steered in extremely
challenging terrain. For a given amount of steering input effort, no other system can
match the power output of a hydro steering system.
Flexibility - the very nature of fluid power (hydraulics) allows for great flexibility in
system design and mounting. The steering need not be constrained by the
requirements for mechanical linkages.
Operator comfort - because of the power generated, required operator input levels
are very low in hydro steering systems.
Control - depending on system design and tuning, precise, custom steering can be
arranged, (for example, a system with very few turns of the steering wheel from lock
to lock)
Weight - the power to weight ratio of hydrostatic systems generally far outstrips
traditional hydraulically boosted mechanically actuated steering systems.
Smoothness - hydro steering systems are smooth and quiet in operation. Vibration
is kept to a minimum. kickback, bump steer, and operator fatigue are all but
eliminated.
Overload protection - when properly designed, automatic valves can guard the
system against a breakdown from overloading
•
•
•
•
•
•

48. The component in the top right of the picture is the
hydraulic steering directional control valve /
metering section; and is the heart of the system

49. Basic wrap-up & Re cap of the
system so far….
• Reservoir - this is the hydraulic fluid (or power
•
steering fluid) reservoir that stores the fluid
necessary for the system.
Supply pump - this is the power steering
pump, note that in many automotive applications
the pump and reservoir are integrated into one
unit

50. How it works (tracing the
circuit).
• The reservoir supplies fluid to the pump. The pump pumps the fluid
•
to the steering unit. When the operator turns the steering wheel,
connected to the steering unit via the steering shaft, the steering
unit directs pressurized fluid to and from the cylinder. In response
the cylinder extends or retracts. The cylinder is connected to the
steered wheels and therefore the wheels steer. Fluid then returns to
the reservoir from the steering unit via the filter.

51. Relief valve
• - This is simply a pressure relief valve. If a
malfunction in the system causes the
pressure to rise too high, the relief valve
opens and the fluid simply passes back to
the reservoir. In virtually all automotive
power steering pumps, the relief valve is
built into the pump

52. Hydraulic Symbols
Definitions of LINES
continuous line - flow
line
dashed line - pilot, drain
envelope - long and short dashes around two or more
component symbols

53. Advanced Hydraulic Symbols

54. Hydraulic Symbols

55. Hydraulic & Pneumatic Symbols
• Some basic symbols:

56. Some Hydraulic & Pneumatic Symbols

57. Some more Hydraulic Symbols

58. Hydraulic Pumps & Motors
Symbols
• More Symbols

59. Hydraulic Pumps
• Any hydraulic pump performs two functions. First, its
•
mechanical action creates a vacuum at the pump inlet
which allows atmospheric pressure to force liquid from
the reservoir into the inlet line to the pump. Second, its
mechanical action delivers this liquid to the pump outlet
and forces it into the hydraulic system.
Shown below is a Variable-displacement, pressurecompensated vane pump

60. Classification of pumps
• All pumps may be classified as either positive•
•
displacement or non-positive-displacement. Most pumps
used in hydraulic systems are positive-displacement.
A non-positive-displacement pump produces a
continuous flow. However, because it does not provide a
positive internal seal against slippage, its output varies
considerably as pressure varies. Centrifugal and
propeller pumps are examples of non-positivedisplacement pumps.
In a positive-displacement pump , slippage is
negligible compared to the pump's volumetric output
flow. If the output port were plugged, pressure would
increase instantaneously to the point that the pump's
pumping element or its case would fail or the pump's
prime mover would stall.

61. Positive-displacement
principle
• A positive-displacement pump is one that
displaces (delivers) the same amount of
liquid for each rotating cycle of the
pumping element. Constant delivery
during each cycle is possible because of
the close-tolerance fit between the
pumping element and the pump case

62. FAULT TRACING OF HYDRAULIC
SYSTEMS
• So in conclusion I may say that to a beginner
an hydraulic system or circuit may look
complicated & fault tracing difficult.
• But if one follows the root cause approach &
checks the system from the basic
parameters then fault tracing is actually
easy.
• However some tools like clip on flow &
pressure gauges, temperature gauges etc
are required.

63. SO, IN HYDRAULICS, AS IN LIFE,
REMEMBER YOUR BASICS & NEVER
GIVE UP
AND LIFE SHALL BE FULL OF
HAPPINESS