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7/27/2019 C - Basic Hydraulics
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Construction & Mining Technique
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Atlas Copco Wagner Inc.
DivisionConstruction & Mining Technique
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Basic
Hydraulics
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Fluid Power System
Fluid Power Systems are power transmittingassemblies employing pressurised liquid or gasto transmit energy.
Fluid power can be divided into two basicdisciplines
> Hydraulics Employing pressurised liquid
> Pneumatics - Employing compressed gas
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What is Hydraulic?
Hydraulics is derived from the Greek word
- Hydor meaning Water
- Aulos meaning Pipe
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Definition of Hydraulic
In simple language:
Confined liquids under pressure made to do work.
OR
Science of transmitting force / motion through themedium of confined liquid
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Definition of Hydraulic
Hydraulics can be divided in to two Sciences :
Hydrodynamic : The science of moving liquid. Thekinetic energy of the moving fluid isused to do work.
Water wheel / Turbine is the example.
Hydrostatics : The science of confined liquid underpressure. The force generated due to
creation of pressure on confinedliquid is used to do work.Hydraulic cylinders is the example.
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Pascal Law
Hydraulic system is based on Pascals law.
Pressure applied on a confined fluid is transmittedin all directions and acts with equal force on all
equal areas and at right angles to them
Pascal Law was named after the French ScientistBlaise Pascal
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Pascals Law - illustration
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Hydraulic Pressworking principle
Realising that a small force on a small areawould create a proportionately larger forceon a larger area, a British mechanic namedJoseph Bramah applied Pascals Law indeveloping an Hydraulic Press.
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Hydraulic Pressworking principle
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Variable speed : Possible to control speed through valve.
Reversible : Instant reverse motion is possible. No need
to stop the system to change direction.
Over load protection : Protected through relief valve from over-loading.
Small package : Components are smaller than other powertransmitting system.
Can be stalled : Not possible on direct drive system fromElectric motor / Diesel engine.
Simple design : Pre-engineered components available.
Self lubricated : Hydraulic oil lubricates the parts.
Flexible : Flexible hoses virtually eliminate the location
problem of the hydraulic components. Smooth : Incompressible, no vibration.
Acts as coolant : It dissipates heat / cools the component,
Acts as seal ; It seals clearances between two mating parts.
Noise free : No noise.
Advantages of oil in Hydraulics
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Functions of Hydraulic Oil
It transmits power.
It lubricates moving parts
It seals clearances betweenmoving parts
It dissipates heat
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Hydraulic System
Reservoir
Filter
Hydraulic Pump
Directional Control Valve
Pressure Control Valve
Actuator (Cylinder/Motor)
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Tank / Reservoir
First a tank is needed to store the hydraulic oil
Reservoir
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Reservoir
Storing oil
Compensates difference in volume whenactuators are used
It dissipates heat
It allows foreign particles to settle down
Baffle separates inlet line with the returnline and allows the air bubbles to escapeto the surface of the oil
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Reservoir
It allows condensed water to settle at the
bottom of the tank
Breather on the top of the tank allows tomaintain atmospheric pressure and
avoid creation of vacuum
Sight glass will indicate the level of theoil. Mercury bulb in it will indicate the oiltemperature
Oil filling inlet will have a filter foravoiding contamination.
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Tank
Pump
Now we need a pump to create flow
Pump
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Pump
Hydraulic Pump is the most importantcomponent in the hydraulic system.
Function of the Hydraulic Pump is to convertMechanical Energy to Hydraulic Energy
Hydraulic Pump are classified in two catagories:
- Hydro-dynamic
- Hydro-static
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Pump
Two types of hydraulic pumps aremost commonly used:
- Rotary Pumps
- Reciprocating Pumps
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Rotary Pumps
Common Pumps in Rotary type are:
- Gear Pumps
- Vane Pumps
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Reciprocating Pumps
Common Pumps in Reciprocatingtype are:
- Axial Piston Pump
- Radial Piston Pump
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TankPump
Actuator
The Actuator (Motor / Cylinder) to work
Actuators
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Actuators
There are mainly two types ofActuators:
- Linear actuators (single acting
cylinders, double acting cylinders)
- Rotary actuators (vane motors,
gear motors, piston motors etc.)
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Tank
Pump
Actuator
Piston reversemovement is not
possible
We need a directioncontrol valve to change
the direction of flow asper requirement
Hoses toconnect thecomponents
Hydraulic System
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Tank
Pump
Actuator
DirectionControl Valve
Hydraulic System
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Valves
Valves are components which guidehydraulic oil delivered by the Pump tothe actuators.
Valves regulate the hydraulic oils
- Volume rate of flow
- Pressure
- Direction
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Valves design
There are mainly two designprinciples for valves
- Spool valves
- Poppet valves
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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 (checkvalve, axial spool valve, ball valve etc.)
- Flow Control Valves (needle valve,throttle check valve etc.)
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Two way Spool valve
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Spool type Four way valve
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Pressure Close - A & B open to tank
A & B Close - Pressure open to tank
Th i i V l
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Three position Valve
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Variable restrictor typeFlow control valve
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Simple Poppet type
Check valve
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Pilot operated
check valve
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Shuttle valve
H d li S t
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Tank
Pump
Actuator
DirectionControl Valve
The control valve is atneutral position
Hydraulic System
H d li S t
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Tank
Pump
Actuator
DirectionControl Valve Now the control valve
is shifted to left
Hydraulic System
H d li S t
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Tank
Pump
Actuator
DirectionControl Valve
To change the pistonmovement in oppositedirection the control
valve is now shifted toright
Hydraulic System
H d li S t
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Tank
Pump
Actuator
DirectionControl Valve
Is it complete circuit ?OR
We need some thing more
Hydraulic System
H dra lic S stem
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Tank
Pump
Actuator
DirectionControl Valve
Piston at end -
No room to move
Pressureincreases
yesWe need some thing moreWe need tocontrol the
system
pressure
Hydraulic System
Hydraulic System
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Tank
Pump
Actuator
Direction
Control Valve
Pressurerelief valve
Hydraulic System
Hydraulic System
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Tank
Pump
Actuator
DirectionControl Valve
Pressure
relief valve
Hydraulic System
Hydraulic System
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Tank
Pump
Actuator
DirectionControl Valve
Stops pressure increasingbeyond the preset value
Pressure
relief valve
Hydraulic System
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Direct acting
Relief valve
Hydraulic System
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Tank
Pump
Actuator
DirectionControl Valve
Now we have a system
which can work
But is this system protectedfrom dirt!!!!
Pressure
relief valve
Hydraulic System
Hydraulic System
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Tank
Pump
Actuator
DirectionControl Valve
We need to protect the systemfrom dirt by installing a FILTERin the system
Filter
We have a system now whichcan work safely
Pressure
relief valve
Hydraulic System
Is filtration necessary?
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Is filtration necessary?
Impurities in the Hydraulic system affect
the the components of the hydraulicsystem and shorten the service life.
Reduction in service life of thecomponents occur in two ways
- Wear and Tear
- Breakdown of component
Filters are used to remove the smallestinsoluble particles and keep thehydraulic system clean
Filters
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Filters
There are basically three types ofFilters
- Suction line filters
- Pressure line filters
- Return line filters
Hydraulic System
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Tank
Pump
Actuator
DirectionControl Valve
Filter
Now we know : Tank contains oil
Filter cleans the system
Pump creates flow
Resistance creates pressure
Actuator to perform the work
Hoses to transmit the oil
D.C. Valve to change directionof oil flow
Relief valve to control the
maximum system pressure.
Pressure
relief valve
Hydraulic System
Hydraulic System
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Tank
Pump
Actuator
DirectionControl Valve
Filter
Few more facts : Pressure increases the system
capacity
Flow increases the systemspeed
Pressure
relief valve
Hydraulic System
Hydraulic System
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Hydraulic jack
LOAD
OIL
Hydraulic System
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