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Landstown High School Governors STEM
& Technology Academy
Advanced Robotics
Chapter 6- Fluid Power Systems
Dr. Barger
Fluid Power Systems
• Fluid power systems use air or liquid, or a
combination of both, to transfer power.
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Fluid Power Systems
• Transfer Methods
– Electrical energy is often used to drive a fluid
pump.
– Electrical energy and mechanical motion are
converted into the energy of a flowing liquid.
• Hydraulic systems use oil, or other liquids, while
pneumatic systems use air.
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Fluid Power Systems
• All fluid power systems consist of:
– Controls,
– An energy source,
– A transmission path,
– A load,
– Indicators,
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Hydraulic System Model
• Hydraulic Systems are used for many
applications in Robotics:
– Operates motors,
– Actuators,
– Cylinders (load devices)
• Usally electrical energy drives a pump
which provides hydraulic pressure,
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Hydraulic System Model
• Prime Mover system
– A prime mover is a component of a power
system that provides the initial power for
movement in the system,,
– The motor receives electrical energy from the
source and converts it to rotary energy or
movement.
– The pump converts the rotary energy into fluid
energy.
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Basic Hydraulic System
LS 6-1
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Hydraulic System Model
• Control Systems
– A typical hydraulic fluid power system includes
a number of control devices,
• Directional control valve (DCV) (cylinders),
• Pressure relief valves,
– A pressure relief valve is a control device that protects
the system from stress and damage caused by over
pressurizing the system.
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Hydraulic Control Devices
LS 6-2
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Pneumatic System Model
• In a typical pneumatic system, the energy source powers a
compressor which forces air into a pressurized storage
tank.
– The compressor is most often driven by an electric motor, or
internal combustion engine.
– The storage tank hold the pressurized air and acts as a reservoir
for the system.
– Typical uses are for:
• Power tools, and
• Lifting and clamping during machining operations.
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Pneumatic System
LS 6-3
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Characteristics of Fluid Flow
• Fluid power systems do not achieve 100
percent power transfer,
– Due to friction from the cylinder walls,
– This friction is known as “resistance” or power
loss,
– Power loss materializes primarily as heat,
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Pneumatic Systems
• Turbulence
– Refers to how the fluid moves through the
fluid power system.
• Conditions of the system, such as:
– size and smoothness of the tubing walls,
– Location and number of valves and fittings,
may cause irregular flow characteristics.
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Pneumatic Systems
• Pressure drops
– Restrictions within the system are also a source of
pressure drops.
• These can be caused by:
– Control valves, tubing length, or small tubing size
• Energy Loss
– As fluid pressure enters the system, it has the ability to
perform a specific amount of work.
– Fluid energy is lost because it is changed into heat due
to friction and resistance.
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Pressure Drops in a Fluid System
LS 6-4
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Pneumatic Systems
• Compression of Fluids
– A notable difference between hydraulic and
pneumatic systems is the compressibility of
the fluids,
• All gases and liquids are compressible under certain
conditions for each,
– Hydraulic fluid is considered incompressible,
– Air in pneumatic systems is readily compressible.
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Principles of Fluid Power
• Pascal’s Law
– Pressure applied to a confined fluid is
transmitted, undiminished, throughout the
fluid.
• This pressure acts on all surfaces of the container,
at right angles to those surfaces,
• For this reason, the walls of the cylinder must be
strong enough to withstand the pressure.
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Pascal’s Law
LS 6-5
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Principles of Fluid Power
• Terminology
– Force
• Is any factor that tends to produce or modify the
motion of an object.
– Inertia- the amount of force needed to produce motion
(or resistance to change) of the body to be moved.
– Pressure
• Is the amount of force applied to a specific area.
Usally in pounds per square inch (psi).
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Principles of Fluid Power
• Fluid Power System Components
– Fluid Pumps
• The heart of a fluid system. It provides an
appropriate flow to develop pressure.
• Two general classifications:
– Positive displacement pump,
» Has a close clearance between the moving member
and stationary pump components,
– Non-Positive displacement pump
» The fluid is moved by the impeller blades during each
revolution.
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Fluid Pumps
LS 6-6
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Principles of Fluid Power
• Examples
–
–
–
–
Reciprocating pumps- Positive displacement,
Rotary Gear Pumps- positive displacement,
Rotary Vane Pumps- positive displacement,
Centrifugal pumps- non-positive displacement,
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Operation of a Reciprocating Pump
LS 6-7
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Rotary Gear Pumps
LS 6-8
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Rotary Vane Pump
LS 6-9
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Centrifugal Pumps
LS 6-10
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Pressure Regulator Valve Operation
LS 6-11
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Principles of Fluid Power
• Fluid Conditioning Devices
– Both hydraulic fluid and air must be
conditioned before being processed through a
fluid power system.
– Conditioning devices prolong the life of fluid
power systems by removing foreign particles
and moisture.
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Principles of Fluid Power
• Hydraulic Conditioning
– The number of components, types of control devices and
operating environment are major considerations in hydraulic fluid
conditioning.
– Types used:
• Strainers- Inline devices,
• Filters- Inline device,
• Heat exchangers– Forced-air fans,
– Water-jacket coolers,
– Gas coolers.
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Principles of Fluid Power
• Pneumatic Conditioning
– Several types of devices are used but the most often is a filtering
device,
• Filters
– Filtering must remove moisture and foreign particles, so they contain
“desiccant”, which is a very dry material designed to attract moisture,
• Lubricators
– Lubricators are devices that add a small quantity of oil to the air
after it leaves the regulator. The lubrication helps the valves and
cylinders operate more efficiently.
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FRL Unit
LS 6-12
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Fluid Power Systems
• Control Devices
– Control is achieved by devices that alter the
pressure, direction and volume of fluid flow.
• Pressure Control
• Flow Control
• Direction Control
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Fluid Check Valve
(Pressure Control)
LS 6-13
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Four-way Valve
(Flow Control)
LS 6-15
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Flow Control Valve Operation
(Direction Control)
LS 6-16
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Principles of Fluid Power
• Load Devices
– The term actuator is often used to identify the
load device.
• Linear Actuators
• Rotary Actuators
• Fluid Motors
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Linear Actuator
LS 6-17
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Rotary Actuators
LS 6-20
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Principles of Fluid Power
• Hybrid Systems
– A number of industrial systems produce
mechanical energy by combining fluid power
and electrical power systems.
– Example:
• Hoists use in car repair operations,
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