Hydraulic and Pneumatic
Circuits
Dr. Omar Mehrez
(PhD) Assistant Professor,
Mechanical Power Engineering Department,
Faculty of Engineering, Tanta University
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- About the Course -
Introduction to Fluid Power
Energy and Power in Hydraulic Systems
Frictional Losses in Hydraulic Pipelines
Hydraulic Pumps
Hydraulic Cylinders and Hydraulic Motors
Hydraulic Valves
Hydraulic Circuit Design and Analysis
Basic Electrical Control of Fluid Power Systems
Reference:
Esposito, A. “Fluid Power with Applications”, England: PEARSON, 2014 2
Hydraulic Motors
Introduction
Limited Rotation Hydraulic Motors
Hydraulic Motors
Hydraulic Motor Performance
Hydrostatic Transmissions
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Introduction
Introduction
Hydraulic cylinders and hydraulic motors extract energy from the
fluid and convert it to mechanical energy to perform useful work.
Hydraulic cylinders (linear actuators) extend or retract a piston rod to
provide a push or pull force to drive the external load through a
straight line
Hydraulic motors (rotary actuators) rotate a shaft to provide a torque
to drive the load along a rotary path Fxv
Hydraulic
Cylinder
VxI Txω PxQ
Electric Hydraulic
Motor Pump
Txω
Hydraulic
Motor
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Introduction
Introduction
Hydraulic Motors
Oscillatory Motors Continuous Motors
(Rotary Actuators) (Hydraulic Motors)
Can rotate clockwise or Can rotate continuously at any rpm
counterclockwise but less than one determined by the motor flow rate
complete revolution
Hydraulic Motor Hydraulic Motor
Rotary Actuator
(Bi-directional) (Uni-directional)
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Hydraulic Motors
Introduction
Limited Rotation Hydraulic Motors
Hydraulic Motors
Hydraulic Motor Performance
Hydrostatic Transmissions
6
Limited Rotation Hydraulic Motors
Introduction
Limited Rotation Hydraulic Motor (Oscillatory Motor / Rotary
Actuator)
Provides a rotary output motion over a finite angle
Produces instantaneous torque in either direction
Requires only a small space and simple mounting
Consists of a chamber or chambers containing the working fluid,
and a movable surface against which the fluid acts
The movable surface is connected to an output shaft to produce the
output motion
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Limited Rotation Hydraulic Motors
Vane Type
Vane Rotary Actuator
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Limited Rotation Hydraulic Motors
Analysis of Torque Capacity
RR: Outer radius of rotor RV: Outer radius of vane
L: Vane width P: hydraulic pressure
F: hydraulic force acting on vane T: Torque capacity
A: surface area of vane in contact with oil VD: Displacement volume
𝑃𝑉𝐷
𝑇=
2𝜋 9
Limited Rotation Hydraulic Motors
Rack-and-Pinion Type
Rack-and-Pinion Rotary Actuator
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Limited Rotation Hydraulic Motors
Applications
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Hydraulic Motors
Introduction
Limited Rotation Hydraulic Motors
Hydraulic Motors
Hydraulic Motor Performance
Hydrostatic Transmissions
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Hydraulic Motors
Introduction
Hydraulic Motors
Can rotate continuously, thus they have the same basic
configurations as pumps
Motors are pushed on by the fluid
Hydraulic motors develop torque and produce continuous
rotatory motion
Three basic types of hydraulic motors:
Gear Motors, Vane Motors, Piston Motors
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Hydraulic Motors
Gear Motor
Theory of operation:
Develops torque due to pressure acting on the surfaces of the gear teeth
The rotation direction can be reversed by reversing the flow direction
Gear motors are only of fixed displacement type
Large side loadings on the shaft and bearing due to high pressure at the inlet
and low pressure at outlet
Simple in design and low cost
Internal gear motor operates under high pressure and speed with greater
displacements
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Hydraulic Motors
Gear Motor
External Gear
Motor
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Hydraulic Motors
Gear Motor
External Gear Motor
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Hydraulic Motors
Vane Motor
Theory of operation:
Develops torque due to pressure acting on vanes surfaces slides in and out of a
rotor connected to drive shaft
Vanes are kept out of the rotor slots using springs or using pressure loaded-vanes
This permits constant contact between the vanes and the came ring especially at
the start of rotation where no centrifugal forces
Vanes motors are universally of the balanced design (and thus of fixed
displacement)
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Hydraulic Motors
Vane Motor
Vane Motor
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Hydraulic Motors
Vane Motor
Balanced vane motors
Vane motors are universally of the balanced design
In this design, pressure buildup at either port is directed to two interconnected
cavities located 180° apart.
The side loads that are created are therefore canceled out. Since vane motors are
hydraulically balanced, they are fixed displacement units.
Vane motors with spring-loaded vanes
A pivoted rocker arms are attached to the rotor
They serve as springs to force the vanes outward against the elliptical cam ring.
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Hydraulic Motors
Vane Motor
Vane motor with spring-
loaded vanes
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Hydraulic Motors
Vane Motor
Balanced Design
Vane Motor
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Hydraulic Motors
In-Line Piston Motor (Swash-Plate Design)
Theory of operation:
Develops torque due to pressure acting on reciprocating pistons
The cylinder block and the motor driveshaft are centered on the same axis
Pressure acting on the pistons generates a force against the angled swash plate
The cylinder block rotates, and generates a torque proportional to the area of
the pistons and the angle of the swash plate
If the swash plate angle is increased, the torque capacity is increased, but the
driveshaft speed is decreased
Both designs are available: fixed displacement and variable displacement
designs
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Hydraulic Motors
In-Line Piston Motor (Swash-Plate Design)
Swash-plate
Piston Motor
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Hydraulic Motors
In-Line Piston Motor (Swash-Plate Design)
𝑃𝑉𝐷
𝑇=
2𝜋
Increasing torque
Increasing the angle Increasing disp. volume
Decreasing speed
Variable Displacement Swash-plate Piston Motor 𝑄𝑇 = 𝑉𝐷 × 𝑁
Hydraulic Motors
In-Line Piston Motor (Swash-Plate Design)
Variable Displacement Swash-plate Piston Motor
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Hydraulic Motors
Axial Piston Motor (Bent-Axis Design)
Theory of operation:
Develops torque due to pressure acting on reciprocating pistons
The cylinder block and the driveshaft mounted at an angle to each other; the
force is exerted on the driveshaft flange
Speed and torque depend on the angle (varies normally 7.5º:30º)
The larger the angle, the greater the displacement and torque but the smaller
the speed.
Both designs are available: fixed displacement and variable displacement
designs
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Hydraulic Motors
Axial Piston Motor (Bent-Axis Design)
Bent Axis Axial Piston Motor 27
Hydraulic Motors
Axial Piston Motor (Bent-Axis Design)
𝑃𝑉𝐷
𝑇=
2𝜋
Increasing torque
Increasing the angle Increasing disp. volume
Decreasing speed
𝑄𝑇 = 𝑉𝐷 × 𝑁
Bent Axis Axial Piston Motor
Hydraulic Motors
Comparison Factors
Gear Motor Vane Motor Piston Motor
Operating
150 bar 170 bar 350 bar
pressure
Operating
2400 rpm 4000 rpm 12000 rpm
speed
Operating
10 L/s 15 L/s 30 L/s
flow rate
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Hydraulic Motors
Introduction
Limited Rotation Hydraulic Motors
Hydraulic Motors
Hydraulic Motor Performance
Hydrostatic Transmissions
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Hydraulic Motor Performance
Hydraulic Motor Efficiencies
1) Volumetric Efficiency ηv:
theortical flow rate motor should consume QT Calculated
v
actual flow rate consumed by motor QA Measured
𝑄𝑇 m3 /s = 𝑉𝐷 (m3 /rev) × 𝑁(rev/s)
2) Mechanical Efficiency ηm:
Actual torque delivered by motor T
m A
torque motor should theortically deliver TT
Theoretical Torque TT:
VD (m3 ) P(Pa)
TT ( Nm)
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Hydraulic Motor Performance
Hydraulic Motor Efficiencies
Actual Torque TA:
actual power delivered by the motor(W)
𝑇𝐴 (Nm) =
𝑁(rad/s)
3) Overall Efficiency ηo:
actual power delivered by motor Brake power
o
actual power delivered to motor Hydraulic power
TA ( N .m) N (rad / s )
o v m
P ( pa )QA (m 3 / s )
Gear Motor (ηo) Vane Motor (ηo) Piston Motor (ηo)
70:75% 75:85% 85:95%
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Hydraulic Motors
Introduction
Limited Rotation Hydraulic Motors
Hydraulic Motors
Hydraulic Motor Performance
Hydrostatic Transmissions
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Hydrostatic Transmissions
Definition
Hydrostatic Transmission: a system consisting of a hydraulic pump, a
hydraulic motor, and appropriate valves and pipes can be used to
provide adjustable-speed drives
Applications:
Tractors, rollers, front-end loaders, and lift truck
Advantages:
Infinitely variable speed and torque in either direction
Extremely high power to weight ratio
Fast response in starting and stopping
Flexibility and simplicity in design 36
Hydrostatic Transmissions
Example: Heavy-Duty Hydrostatic Transmission
Variable disp. Swash Construction Fixed disp. Swash
plate piston pump plate piston motor
The operator has complete control of the system with one lever for starting,
stopping, forward or reverse motion
Controlling the variable displacement pump
• Speed of the output shaft is controlled by adjusting the displacement
(flow) of the pump
• Load (working pressure) is determined by the demand of the system
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Hydrostatic Transmissions
Hydrostatic
Transmission
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Hydrostatic Transmissions
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Hydrostatic Transmissions
Example
A hydrostatic transmission, operating at 70 bars pressure, has the following
characteristics:
Pump Hydraulic Motor
VD = 82 cm3 VD = ?
ηv = 82% ηv = 92%
ηm = 88% ηm = 90%
N = 500 rpm N = 400 rpm
Find the:
a) The displacement of the motor
b) Motor output torque
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Hydrostatic Transmissions
Example
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Hydrostatic Transmissions
Example
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Summary
Explain the operation of limited rotation hydraulic motors
Explain the operation of gear, vane, and piston hydraulic motors
Evaluate the performance of hydraulic motors by the determination
of the volumetric, mechanical and overall efficiencies
Determination of the torque and power delivered by hydraulic
motors
Analyze the operation and performance of hydrostatic transmission
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THANK YOU
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