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Introduction to Fluid Power
Mohammad I. KilaniMechatronics Engineering Department
University of Jordan
What is Fluid Power
Hydraulic and fluidic power are used extensively in today’s industry. In many applications, small amount of power or energy is used to control and transmit very large amounts of power.
Airplanes, car jacks, and bulldozers and robots depend on fluid power to operate numerous subsystems needed in their operation.
Fluid power systems control with the delicacy of a feather touch, tens of kilowatts required in the operation of these systems.
Hydraulic Basic Principles
Hydraulics is the technology or study of liquid pressure and flow. Liquids are materials which pour and conform to the shape of their container. Example are oil and water at room temperature.
Stationary fluids provide no resistance to shear stresses. This allows fluids to take the shape of the container they are in, and also leads to Pascal’s law, which states that the pressure at any given point in a fluid is the same in all directions.
Pressure applied to a confined fluid is transmitted undiminished in all directions, and acts with equal force on equal areas, and at right angles to them.
Prove Pascal’s law
10 N Force
1 square cm stopper
10 N per square cm
Pressure of 100 kPa
Multiplication of Force
Since liquid transmit the same amount of pressure in all directions. The force transmitted to the output piston is multiplied by a factor equal to the area ratio of the output piston to the input piston
Multiplication of Force
Even though force is multiplied, the power or energy is not. In fact, the energy or power input is usually larger than the obtained output.
The transmission ratio is defined as the velocity at the input to that at the output in case of no leakage, and is a function of the geometry of the setup. The ratio of the output force to the input force is usually less than the transmission ratio due to frictional losses.
An Introductory Fluid Power System
Lifting and Lowering a Load
Introduction to Fluid Power
Directional Control Valve in Load Lifting Position
An Introductory Fluid Power System: Load Raising
Directional Control Valve in Load Lowering Position
An Introductory Fluid Power System: Load Lowering
Directional Control Valve in Load Locked Position
An Introductory Fluid Power System: Locked Position
An Introductory Fluid Power System:Directional Control Valve
Four WayThree Position
Manually (Lever) OperatedSpring Centered ,
Directional Control Valve
An Introductory Fluid Power System: Symbolic Presentation
Fload
Operation of a Basic Hydraulic Circuit
When the directional control valve lever is moved upward, the pumped oil flows through path P – B of the to the lower part of the cylinder.
Since the oil is under pressure, it pushes up the piston inside the cylinder, causing the piston rod to retract, and the load to be raised. The oil in the upper side of the piston is drained back to the reservoir through path A – T of the directional control valve.
Operation of a Basic Hydraulic Circuit
When the directional control valve lever is centered, all four ports are blocked and oil can not escape from either side of the cylinder. This stops the movement of the piston and causes the oil to flow from the pump back to the reservoir through the pressure relief valve.
The pressure in the lower end of the cylinder will be at an intermediate level due to the presence of the load.
Operation of a Basic Hydraulic Circuit
When the directional control valve lever is moved toward the valve body, the pumped oil flows through the path P – A of the directional control valve to the upper end of the cylinder. The oil pushes the piston downward, which lowers the attached load.
The oil in the lower end of the cylinder of the piston is drained back to the reservoir through path B – T of the directional control valve.
As an Engineer, what issues will you be concerned about in the presented system
1 minute to write on a piece of paper!
An Introductory Fluid Power System: Engineering Issues
An Introductory Fluid Power System: Basic Performance
1. How much load will the system be able to raise? 2. How fast does the load go up? 3. Is it possible to control lifting and lowering speeds? How?
An Introductory Fluid Power System:Efficiency/Operating Cost Issues
1. How much power will I need for (i) raising the load, (ii) lowering the load, and (iii) stopping the load?
1. What is the needed pressure at the pump outlet?2. What is the pressure at the pump inlet?
2. Can I make the system more efficient, particularly during lowering and stopping the load
An Introductory Fluid Power System: Safety Issues
1. Is the system safe enough?2. What happens in case of hydraulic line rupture, pump failure, or
electrical power shutdown in the position shown?
An Introductory Fluid Power System:Expansion Issues
1. Is it possible to give the cylinder a command position, and have it go to that position automatically, without operator intervention?
2. Can I have two or more cylinders work in tandem?3. Can I have two or more cylinders work in series?
Work and Power
How much power can a person produce?
What experiments would you perform to estimate your own power production?
Introduction to Fluid Power
Work and Power
A person is required to lift a 50 N box a distance of 2 m. The work done by this person is given by:
Work = Force x Displacement
Work = 50 N x 2 m = 100 N.m (Joule) If the person is asked to raise the box in 2
second. How much power is he producing? Power is the time rate of doing work.
Power = Work/time
Power = 100 J/2 s = 50 J/s (Watt) A person doing the same work in 1 seconds
produces 100 W of power How much power can a person produce?
Power Produced by a Weight Lifter
The Power produced by popular weight lifters during the lift process ranges between 2 – 2.5 kW
Weight Lifter Disc Mass (kg)
Force (N) Lift Distance* (m)
Lift Time (s)
Power (W)
Vakhonin 130 1275.3 2 1 2550.6
Fukuda 130 1275.3 2 1.3125 1943.3
Berger 140 1373.4 2 1.375 1997.7
Mryake 151 1481.31 2 1.5 1975.1
*Estimated
http://mapawatt.com/wp-content/uploads/2009/07/Hour-watts-power-output.jpg
Power Produced By a Cyclist
Average power for the first 30 seconds is 300 W
Power Produced By a Horse
1 Horsepower = 745.6 W
Lifting a 70 kg man at 23 km/h up a 10 degree slope
Power Produced By an Automobile Engine
Make and Model EnginePower @ 6000 rpm
hp kW
Toyota Corolla 1.8 L, 4-cylinder 132 98.4Mercedes Benz C-Class 1.8 L, 4-cylinder 153 114.1
Toyota Camry 2.5 L , 4-cylinder 178 132.7
Lexus 3.5 L, 6-cylinder 306 228.1
Other Applications Requiring Work and Power
Introduction to Fluid Power
Applications requiring work and power
Lift a load against gravity Manufacturing processes: (metal
forming, cutting, punching, deep drawing, cutting, turning, milling, etc. involves applying a force for a certain distance.
Changing the speed of an object Moving objects against friction,
air drag, water drag: e.g., car, ships, airplanes, etc.
Walking, speaking, etc.
How much power can a person produce?
Power Conversion andPower Transmissions
Introduction to Fluid Power
Forms of Power
Power Form Potential Variable Flow Variable
Mechanical Linear Force (F) Linear velocity (v)
Mechanical Rotational Torque (T) Angular Speed (ω)
Fluid Pressure (P) Flow Rate (Q)
Electrical Voltage (V) Electric Current (I)
Power Converters – Electromechanical
Mechanical to Electric
Electric GeneratorT x ωF x v V x I
Electric MotorLinear Electric Actuator
T x ωF x vV x I
Electric to Mechanical
Power Converters – Hydromechanical
Mechanical to Fluid
PumpT x ωF x v P x Q
Rotary ActuatorLinear Actuator
T x ωF x vP x Q
Fluid to Mechanical
Power Transmitters – Direct Power Transmission
Power TransmitterTi x ωi
Fi x vi
To x ωo
Fo x vo
Why would we perform power transmission?
Give Some Examples on power transmission devices
Reasons for Power Transmission
Manipulation of the values of the potential – flow variable, e.g. when the potential variable at the load (torque or force) is not compatible with the source (too high or too low)
Load is placed at a location different from that of the source. Need to “Transport” power from the source location to the load location
Power Transmitter
Ti x ωi
Fi x vi
To x ωo
Fo x vo
Direct Power Transmission
Direct (Mechanical)
Examples:1. Mechanical Linkages: (Levers, mechanisms, etc.)2. Pulleys and Ropes3. Sprockets and Chains4. Gear Boxes5. Belt Drives
Power TransmitterTi x ωi
Fi x vi
To x ωo
Fo x vo
Indirect Power Transmitters(Back – to – Back Converter)
Power Converter
Power Converter
Pneumatic
Electric
Hydraulic
Ti x ωi
Fi x vi
To x ωo
Fo x vo
Power Transmission Methods
Direct (Mechanical) Gear trains and shafts Levers and linkages Ropes and Pulleys Chains and Sprockets Belt Drives
Indirect (Back to Back) Electric
(Generators – Transformers – Motors) Hydraulic
(Pump – Hydraulic motor or hydraulic actuator) Pneumatic
(Compressor – Pneumatic cylinder)
PowerTransmitter
Ti x ωi
Fi x vi
To x ωo
Fo x vo
We define the speed magnification ratio, for a power transmitter as the ratio of the output speed to the input speed.
If the power transmission system is ideal, the output power is equal to the input power (no losses), then
Transmission Ratio
Rotational Power Transmitter
Ti x ωi To x ωooiS
iiiSo
iioo
TTr
ωTωrT
ωTωT
ioSr Linear PowerTransmitter
Fi x vi Fo x voioS vvr
oiS
iiiSo
iioo
FFr
vFvrF
vFvF
In a number of power transmission systems, a definite relationship exists between the input motion and the output motion. This relationship is maintained by a set of constraints provided in the transmission system.
Example constraints in mechanical power transmission systems include the constant distance between any two points in a rigid body, the equal displacement of the two pitch points on the pitch circles of two gears in mesh, and the constant length of ropes and chain sprockets in rope-pulleys and chain-sprocket drives.
In hydraulic power transmission systems, input – output motion constraint is provided by the incompressibility of the hydraulic fluid in the system and the conservation of mass principle
Transmission Ratio
di do
Fi
Fo
O
A B
rvv
ddvvr
dvdv
io
oioi
ooii
If the arm of the lever mechanism is treated as a rigid body, the constant distance constraint means that the angular displacement (Δϴ) is the same for all lines in the body. This means that the angular speed (ω = dϴ/dt) is the same for all points in the lever.
We define the transmission ratio as the ratio of input speed to output speed. This ratio is sometimes called the speed reduction ratio.
Transmission Ratio
di do
Fi
Fo
O
A B
rvv
ddvvr
dvdv
io
oioi
ooii
If no power losses exist (no friction), the output power produced by the lever is equal to the input power. Therefore, we have
The mechanical advantage or the force amplification ratio is the ratio of the ideal output force to the input force. In an ideal transmitter with no power loss, the mechanical advantage is equal to the speed reduction ratio.
Transmission Ratio
iidealo
iiiidealo
iioidealo
rFF
vFrvF
vFvF
,
,
,
iidealo TTr , iidealo FFr ,oi
iioi
iioidealo
ωωr
ωTωrT
ωTωT
,
oi
iioi
iiidealoo
vvr
vFvrF
vFvF
di do
Fi
Fo
O
A B
Transmission Ratio
Rotational Power Transmitter
Ti x ωi To x ωo
Linear PowerTransmitter
Fi x vi Fo x vo
For an ideal transmission system, the torque (force) amplification ratio is equal to the speed reduction ratio. This ratio is called the transmission ratio and it is completely defined by the geometry of the system.
oi
iioi
iiidealoo
ωωr
ωTωrT
ωTωT
oi
iioi
iiidealoo
vvr
vFvrF
vFvF
Transmission Ratio
Linear PowerTransmitter
Fi x vi Fo x vo
oiio
ooii
o
ddFFr
dFdF
M
0
oioi
ooii
ddvvr
dvdv
di do
Fi
Fo
O
Transmission Ratio
rrrTT
FrTrT
rFT
M
rFT
M
ioio
Cooii
oCo
B
iCi
A
0
0
ro
To
ri
Ti
FC
FC
B
A
Rotational PowerTransmitter
Ti x viTo x vo
rrr
vrr
iooi
ooii
The overall efficiency is defined is the ratio of the power produced by the system to the power delivered to the system
For an ideal power transmission systems with no frictional losses, Ti and To are related by To = rTi . If the system is also a non-slipping mechanical system or a non-leaking converter, the following relation hold.
Overall Efficiency
PowerTransmitter
Ti x ωi To x ωo
ii
oo
i
ooverall T
T
P
P
i
o
idealo
omech rT
T
T
T
,
rTT
rTT
oideali
iidealo
,
,
r
rTT
io
io
1
ii
ii
i
ooverall T
rrT
P
P
When frictional losses exist the torque produced by the transmitter is less than that of an ideal frictionless transmitter, (To < rTi). The mechanical efficiency is defined as the ratio of the output torque produced by the system to the torque produced by an ideal frictionless transmitter for the same torque input.
The mechanical efficiency is also the ratio between the ideal input torque needed by a frictionless system to the actual input torque needed by the system to produce the same torque output.
Mechanical Efficiency
PowerTransmitter
Ti x ωi To x ωo
i
ideali
i
o
idealo
omech T
T
rT
T
T
T ,
,
rTT
rTT
oideali
iidealo
,
,
For non-slipping mechanical transmitters (gear trains, levers, pulleys and chain-sprocket), the speed ratio relation, ωo = ωi /r, holds regardless of frictional loss. This relation is also valid for non-leaking back-to-back converters based on mass/current conservation. When the systems have slippage or leakage, the output speed is reduced. The volumetric Efficiency is defined as:
Volumetric Efficiency
PowerTransmitter
Ti x ωi To x ωo
r
r
oideali
iidealo
,
,
i
ideali
i
o
idealo
ovol r
,
,
The overall efficiency may be written in terms of the mechanical efficiency and the volumetric efficiency by utilizing the relationships
Efficiency Relationships
PowerTransmitter
Ti x ωi To x ωo
rTT
rTT
idealoi
iidealo
,
,
volmechidealo
o
idealo
ooverall
idealoidealo
oo
ii
oo
i
ooverall
T
T
rrT
T
T
T
P
P
,,
,,
idealoi
iidealo
r
r
,
,
Power Transmission Comparison Factor
Introduction to Fluid Power
What factors will you consider when comparing the different methods of power transmission?
PowerTransmitter
Ti x ωi To x ωo
Comparison Factors: Transmission Distance
Effect on initial cost (capital)
Effect on running cost (transmission efficiency )
PowerTransmitter
Ti x ωi To x ωo
Comparison Factors: Transmission Ratio
What is the effect of increased transmission ratio on initial cost (capital)?
What is the effect of increased transmission ratio on running cost (transmission efficiency)?
Is there a practical limit on the maximum transmission ratio provided that may be provided by the system?
PowerTransmitter
Ti x ωi To x ωo
Comparison Factors: Outlet speed variation
Does the system allow the outlet speed to be varied?
Is output speed variation continuous or in discrete steps
What is the effect on initial cost
What is the effect on running cost (transmission efficiency)
PowerTransmitter
Ti x ωi To x ωo
Comparison Factors: Outlet torque or force variation
How does the system respond to variations in the outlet load?
Will the system stall if the load is increased beyond a certain level?
PowerTransmitter
Ti x ωi To x ωo
Comparison Factors: Distribution
Does the system allow the outlet power to be distributed among a number of terminals?
Does it have the flexibility to allow control of the amount of power delivered at each terminal, either continuously, or in discrete steps
What is the effect of distribution on initial cost and on running cost (transmission efficiency )
PowerTransmitter
T x ωF x v
T1 x ω1
T2 x ω2
Tn x ωn
Comparison Factors: Leakage
How much leakage does the system has? Is it leak free?
Effect on power cost and material cost
PowerTransmitter
T x ωF x v
T1 x ω1
T2 x ω2
Tn x ωn
volmechoverall
idealleakagevol
ideal
leakageidealvol
ideal
actualvol
Q
Q
Q
1
Comparison Factors: Noise
How much noise does the system produce
PowerTransmitter
T x ωF x v
T1 x ω1
T2 x ω2
Tn x ωn
Comparison Factors: Safety
How safe is the system? What happens in case of
overload? What happens in case of
tube rupture, mechanical failure?
PowerTransmitter
T x ωF x v
T1 x ω1
T2 x ω2
Tn x ωn
Advantages of Fluid Power
High Transmission Ratio:A fluid power system can multiply forces simply and efficiently several thousands of times in a compact setup.
Simplicity, compactness and light weightFluid power systems use fewer number of moving parts than comparable mechanical or electrical systems. Thus they are simpler to maintain and operate. This also increases reliability and allows compactness and light weight of the system.
1 square cmcylinder
Advantages of Fluid Power
Constant Force or Torque:Fluid power systems are capable of providing constant force or torque regardless of speed changes.
Ease and Accuracy of Control:By the use of simple control valves operated by manually or electrically, the operator of a fluid power system can readily start, stop, speed up and slow down desired equipment.
Safety:A consequence of simplicity, overloads can be easily controlled by relief valves
1 square cmcylinder
Advantages of Fluid Power
Flexibility:Unlike mechanical methods of power transmission where the relative position of the engine and the work site must remain relatively constant, the flexibility of hydraulic lines allow power be moved flexibly wherever needed.
Economy:This is the natural result of the previous factors, particularly simplicity and compactness. Fluid power systems provide an relatively low cost method for power transmission. Also, power and frictional losses are comparatively small.
Drawbacks of Fluid Power Systems
Fluid power systems have some drawbacks. Hydraulic systems suffer from messy oil, and leakage which is impossible to eliminate completely.
Hydraulic lines can burst resulting in possible injury or fire.
Hydraulics and pneumatic systems employ pumps or compressors, which tend to generate noise.
For short distance transmission, hydraulic and pneumatic power transmission systems are usually less efficient than mechanical transmission systems. They are, however, typically more efficient than electrical power transmission systems.
For long distamce transmission, electrical power comes first, followed by hydraiulic.
Comparison of individual factors for power transmission methods
The commonly used power transmission methods in the industry are electric, mechanical, pneumatic and hydraulic.
These methods may be compared with respect to energy production, storage transportation and cost, leakage and environmental effects, ability to generate linear, angular and rotary motion, ability to provide linear and rotary thrusts, controllability, handling and noise
Advantages of Fluid Power
Compared to electrical and mechanical power transmission, fluid power transmission offers versatility and manageability advantages allowing it to be an economic and efficient candidate for a number of application.
Industry is moving toward automating its operation in order to increase productivity, accuracy and consistency. Fluid power will be an essential element in industrial automation for the foreseen future.
What is Fluid Power
Aviation is an industry that relies heavily on hydraulics.
Aircraft hydraulic systems are lightweight and compact, yet powerful enough to move the control surfaces of the wings of the largest planes.
Components of a Basic Hydraulic Circuit
A hydraulic circuit is a path for oil or hydraulic fluid to flow through a set of basic components. These components are:
The reservoir or an oil tank that hold the oil. The pump that pushes the oil and increases its pressure. An electric motor or other power source to drive the pump The directional control valve, which controls the direction of oil flow to the
cylinder. The hydraulic cylinder which converts fluid energy into linear mechanical
energy. The relief valve, which limits the system pressure to a safe level by allowing oil
to flow directly from the pump back to the reservoir when the pressure at the pump output reaches a certain level.
The piping which carry oil from one location to another
Components of a Basic Pneumatic Circuit
A hydraulic circuit is a path for oil or hydraulic fluid to flow through a set of basic components. These components are:
An Air Tank that stores a given volume of compressed air.
A compressor that compresses the air coming from atmosphere
An electric motor or other prime mover to drive the compressor.
The directional control valve, which controls the direction of oil flow to the cylinder.
The hydraulic cylinder which converts fluid energy into linear mechanical energy.
The relief valve, which limits the system pressure to a safe level by allowing oil to flow directly from the pump back to the reservoir when the pressure at the pump output reaches a certain level
Example Pneumatic Circuits
Introduction to Fluid Power
Direct Control of a Single Acting Cylinder – Extension
List of equipment
01 Air service unit (filter with water separator, pressure regulator and pressure gauge) with 3/2 directional control ball valve
02 Distributor, 6-fold
03 Single-acting cylinder
06 3/2 directional control valve with manually operated push-button
21 Pressure gauge
Direct Control of a Single Acting Cylinder – Extension
The piston rod of the single-acting cylinder extends when the button of the directional control valve is pushed. The rod remains extended as long as the button is pushed.
The piston retracts when the button is released
The active pressure of the cylinder appears on the pressure gauge.
Direct Control of a Single Acting Cylinder – Retraction
List of equipment
01 Air service unit (filter with water separator, pressure regulator and pressure gauge) with 3/2 directional control ball valve
02 Distributor, 6-fold
03 Single-acting cylinder
07 3/2 directional control valve with manually operated push-button
Direct Control of a Single Acting Cylinder – Retraction
The default position of the piston rod of the single-acting cylinder is extension when the compressed air supply is switched on.
When the push button of the directional control valve is actuated, the piston retracts and remain retracted.
The piston returns to its extended position when the pushbutton is released
Direct Control of a Single Acting Cylinder – Retraction
Video
Direct Control of a Single Acting Cylinder
Retraction
Introduction to Fluid Power
Projects (5 points)
Video Recording of your Lab Experiments
Introduction to Fluid Power
Example
Spiral Pump Video
Introduction to Fluid Power
Power Transmission Comparison Tables
Introduction to Fluid Power
Energy Source
Pneumatic Hydraulic Mechanical Electrical
Stationary or mobile air compressor plant, electric motor or internal combustion engine drive. Compressor selected based on pressure and capacity. Air for compressor available everywhere with unlimited supply.
Stationary or mobile pump plant, electric motor drive, rarely internal combustion engine driving generator and motor. Minimum duty units also manually operated. Pump type selected based on required pressure and capacity
Stationary or mobile electric motor or internal combustion engine. Some units manually operated. Motor selected based on power and torque requirements.
Usually relies on regional power grid tied to site consideration (hydro, fossil fuel, or power plants)
Energy Storage
Pneumatic Hydraulic Mechanical Electrical
Large quantities can be stored economically by compressed air cylinders.
Limited storage capability by accumulators and compressed air as an auxiliary medium. Economical only for small quantities
Possible to store intermediate amounts of power by a flywheel.
Highly difficult and elaborate to store. Minimal quantities may be stored using batteries of fuel cells
Energy Transportation
Pneumatic Hydraulic Mechanical Electrical
Readily transportable through piping up to distances of about 1000 meters without loss of pressure.
Can be transported through piping up to distances of about 100 meters without loss of pressure
Transportation possible efficiently over limited distances through an axle. Frictional losses reduce efficiency for large distances
Easily transported over unlimited distances
Energy Transmission
Pneumatic Hydraulic Mechanical Electrical
Piston – cylinder arrangements allow efficient transmission of flow rate and pressure heads.
Piston – cylinder arrangements allow efficient transmission of flow rate and pressure heads.
Geared transmissions allow torque – speed manipulation with high efficiency
Ac voltages and currents can be easily transmitted by a transformer
Leakage
Pneumatic Hydraulic Mechanical Electrical
Piston – cylinder arrangements allow efficient transmission of flow rate and pressure heads.
Loss of energy and substantial effect on environment due to leaking hydraulic fluid with accident risks
Loss of energy possible due to friction for long transportation paths. Accident risk due to moving mechanical parts.
No loss of energy without conductive paths or parts. Lethal accident risk at high voltages.
Effect of Environment
Pneumatic Hydraulic Mechanical Electrical
Compressed air is insensitive to temperature fluctuations. No fire or explosion hazard. Risk of icing at low ambient temperature, high humidity and high flow velocities.
Sensitive to variations in temperature. Fire hazards entailed with oil leakage.
Temperature fluctuations may affect performance. Special treatment necessary in corrosive or humid environments
Insensitive to temperature variations in normal range. Additional protective measures are required in fire or explosion-hazard areas.
Linear Motion
Pneumatic Hydraulic Mechanical Electrical
Convenient with cylinders. Strokes up to 2000 mm. High acceleration and deceleration. Speeds
Convenient with cylinders. Well amenable to control in slow speed range.
Rack and pinion, lead screw and nut, and other mechanical linkages provide wide selection of linear motions
Short travel only with solenoids or linear motors.
Rotary Motion
Pneumatic Hydraulic Mechanical Electrical
Air motors of various types. Wide range of speed up to 500,000 rpm, and higher. Simple reversal of rotation.
Hydraulic motors of various types. Smaller speed range than air motors, but better control in slow speed range
Best efficiency by rotary drives or motors. Internal combustion engines also readily provide rotary motion
Best efficiency by rotary drives or motors.
Angular Motion
Pneumatic Hydraulic Mechanical Electrical
Conveniently obtained with cylinders or swivel actuators, up to 360 degrees and more.
Conveniently obtained with cylinders or swivel actuators, up to 360 degrees and more.
Translated from rotary motion through mechanical linkage.
Translated from rotary motion through mechanical linkage.
Linear Thrust
Pneumatic Hydraulic Mechanical Electrical
Narrow range of force due to low pressure. Overload protection up to standstill. No energy consumption for holding force. Economical for thrusts from 1 N to 50 kN.
High forces available due to high pressure. Overload protection by relief valves. Continuous energy consumption for holding forces.
Rack and pinion, lead screw and nut, and other mechanical linkages provide wide selection of linear motions with intermediate linear thrust. Difficult overload protection
Mechanical linkage needed for energy transmission. Rack and pinion may result in poor efficiency.
Rotary Thrust
Pneumatic Hydraulic Mechanical Electrical
Full torque even at standstill without energy consumption. Overload protection without drawbacks. Narrow range of force.
Full torque even at standstill, but less efficiency. Overload protection by relief valve. Wide range of torques.
Force multiplication by geared transmission
Minimum torque at standstill. Cannot be overloaded, small range of force
Controllability
Pneumatic Hydraulic Mechanical Electrical
Thrust conveniently controlled through pressure reducing valves in range 1:10 dependent on load. Speed conveniently controlled through restrictor valves or quick exhaust valves, poor reduction in low range.
Thrust conveniently controlled through pressure reducing valves over a wide range. Speed control very good and precise in low range.
Limited means of control. Highly elaborate.
Limited means of control. Highly elaborate.
Noise
Pneumatic Hydraulic Mechanical Electrical
Exhaust noise unpleasant but can be greatly reduced by installing silencers.
Pump noise at high pressure. Noise conducted through rigid piping
Within limits of workshop noise. Noise can be reduced or eliminated by proper lubrication and design.
Loud actuation noise of contactors, otherwise within limits of workshop noise.
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