INTRODUCTION :-
Since ancient times man has used fluid power to ease his burden.Pumps and water wheels are known to man since ancient days.In the 17th century we came across a revolutionary law which changed the fate of hydraulics in the following years to come.One after another most of the sophisticated hydraulics systems were discovered and now in the 21st century we cannot live with out hydraulic systems.
French scientist Pascal illustrated the use of confined fluids for transmitting power and multiplying forces.
Pascal's law :-
Pascal's law states that when there is an increase in pressure at any point in a confined fluid, there is an equal increase at every other point in the container.
In simple terms pressure applied on a confined fluid is transmitted undiminished in all directions,and acts with equal force on equal areas and at right angles to them.
example:- one of the simple example is when we push the the stopper of a already full bottle filled with fluid then we can break the bottom of the bottle with very moderate force.As the bottle neck has very small cross sectional area, the force exerted there will be multiplied at the bottom of the bottle which has large cross sectional area.
As the pressure at both ends are same we have the force multiplied at the bottom of the bottle to break it.
pressure is defined as the force per unit area ( area must be perpendicular to the direction of the force)
PRESSURE = FORCE / AREA NORMAL TO THE DIRECTION OF FORCE APPLIED.
Simplest example of pascal,s law is a hydraulic press.
pascal,s law does not violate the conservation of energy.It is not like we get some thing for nothing.Here in the previous example we get the same volume of fluid displaced at the both end of the hydraulic press proportionate to there area.So what is gained in the multiplied force must be sacrificed in the distance.
HYDRAULIC POWER TRANSMISSION :-
ADVANTAGES OF A HYDRAULIC POWER TRANSFER :-
The advantages of hydraulic system are.
1. Reversibility :-Only few prime movers are reversible.And for the reversible operation they need to be completely stopped or slowed,But in case of hydraulic system it can be versed in full motion with out damage.A directional valve or a reversible pump gives the reversible control and a relief valve protects the system from overload.
2. Variable speed:-Most of the prime movers are desired to run at constant speed but we need our actuator to run at variable speed.In hydraulic system has a advantage that the actuator can be driven at variable speed by controling the delivery of pump by a flow control valve.
3. Overload protection :-In hydraulic systems we have pressure relief valve which protects the system from overload damage.
4. System can be easily stalled:- An electric motor can not be stalled without blowing a fuse or an engine can not be stalled without a requirement for restarting it.But ahydraulic system can be stalled while the system is running by just bypassing the flow to the reservoir. It again works automatically when the system overload is reduced.
5. Very compact packages :- hydraulic system is very compact and easy to handle and mount in the system.
The name hydraulics in fact comes from Greek word ,HYDRO means Water and AULOS means pipe.
The hydraulic power transmission is instant because the transfer medium is fluid which is incompressible or very slightly compressible.some of the hydraulic presses use water as the medium but normally in power hydraulics we use petroleum oil because of its lubricating ability and very slight compressibility. Even in 1000 psi it will only compress about 0.5 % of its volume is not it great.
HOW PRESSURE IS CREATED ?
It is a common thinking that pressure is created by the pump and pump is always blamed for the pressure problems but it is not true.
***pump never creates pressure it only creates a flow.The restriction to the flow creates the pressure.
For example if the system has no load or no friction then the pressure gauge fitted in the system will show zero pressure.It means the pump will deliver the same amount of flow regardless the pressure.
for example in the above figure the pressure in the system is force per unit area i.e 8000 lb/10 square inch = 800 psi.If there is a leakage in the system then also the pressure is 800 psi.A leakage in the system only decrease the efficiency of the pump but not the pressure.
Hence any restriction to the flow of fluid creates the pressure like an orifice or a load or friction in the pipe in which the flow is occurring.The inherent property of fluid is to follow the least resistance path.If the flow is occurring in a parallel flow path then the pressure in the system will show same as the pressure created by the least resistance flow path.
But in case of series of resistance the pressure before the first resistance will be same as the sum of all the resistance in the path to be followed and so on.
SOME OF THE TERMS AND FORMULAE RELATED OF HYDRAULIC COMPONENTS :
1. FORCE IS PROPORTIONAL TO PRESSURE AND AREA.
F = P * A
F = APPLIED FORCE (POUND OR lb)
A= NORMAL AREA IN CONTACT WITH THE FORCE (INCH SQUARE)
P= THE PRESSURE (POUND PER SQUARE INCH)
2. SPEED OF AN ACTUATOR DEPENDS ON THE CYLINDER SIZE AND THE RATE OF FLOW IN TO IT.
SPEED = (VOLUME/ TIME) / AREA
3. VELOCITY OF FLOW IN PIPES VARIES INVERSELY AS SQUARE OF INSIDE DIAMETER OF THE PIPE.USUALLY FRICTION OF FLUID FLOWING THROUGH PIPE IS PROPORTIONAL TO VELOCITY BUT IN CASE OF TURBULENT FLOW IT VARIES AS THE SQUARE OF IT'S VELOCITY.
4. IF THE FLOW GPM (GALLON PER MINUTE) AND VELOCITY(FEET PER SECOND) ARE KNOWN THEN USE THIS RELATIONSHIP TO FINE THE CROSS SECTIONAL AREA OF THE PIPE.
AREA = (GPM * 0.3208)/ VELOCITY IN FEET PER SECOND.
AREA = (LPM * 16667 )/ VELOCITY IN MM PER SECOND.
=> VELOCITY = GPM/(3.117 *AREA IN INCH SQUARE)
=> VELOCITY = LPM /(16667 * AREA IN MM SQUARE)
5. POWER = (FORCE * DISTANCE) / TIME
UNIT OF POWER IS HORSE POWER .ONE HORSE POWER OR hp IS EQUIVALENT TO 33000 lb LIFTED IN ONE MINUTE TO ONE FEET HEIGHT.
=> 1 hp = 33,000 lb feet /min = 550 lb ft / sec
1 watt = 1 N m /sec
=> 1 hp = 746 watt
IN HYDRAULIC SYSTEM POWER IS EQUAL TO
POWER = FLOW * PRESSURE
=>POWER = GPM * (POUNDS / SQ INCH )
=> HORSE POWER (hp) = GPM * PSI * 0.0007
=> KILOWATT = LPM * BAR * 0.002
6. HP = (TORQUE * RPM ) / 63025
KILOWATT = (TORQUE * RPM) / 9550
to be continued..........................................
learn and enjoy.....
In simple terms pressure applied on a confined fluid is transmitted undiminished in all directions,and acts with equal force on equal areas and at right angles to them.
example:- one of the simple example is when we push the the stopper of a already full bottle filled with fluid then we can break the bottom of the bottle with very moderate force.As the bottle neck has very small cross sectional area, the force exerted there will be multiplied at the bottom of the bottle which has large cross sectional area.
As the pressure at both ends are same we have the force multiplied at the bottom of the bottle to break it.
pressure is defined as the force per unit area ( area must be perpendicular to the direction of the force)
PRESSURE = FORCE / AREA NORMAL TO THE DIRECTION OF FORCE APPLIED.
Simplest example of pascal,s law is a hydraulic press.
pascal,s law does not violate the conservation of energy.It is not like we get some thing for nothing.Here in the previous example we get the same volume of fluid displaced at the both end of the hydraulic press proportionate to there area.So what is gained in the multiplied force must be sacrificed in the distance.
HYDRAULIC POWER TRANSMISSION :-
Hydraulics now could be defined as a means of transmitting power by pushing a confined fluid .The input component is called pump and the output component is called the actuator.
Hydraulic system is not a source of power.The exact source of power is the prime mover may be electric motor of an engine which drive the pump (the input of the hydraulic system). Hence a question might arise in the reader's mind that if hydraulic system is not the source of power then forget about hydraulics ,and one can directly transmit power through mechanical linkages and solve the purpose.
But,it is the versatility of the hydraulic system which has made it so popular now a days.
Hydraulic system is not a source of power.The exact source of power is the prime mover may be electric motor of an engine which drive the pump (the input of the hydraulic system). Hence a question might arise in the reader's mind that if hydraulic system is not the source of power then forget about hydraulics ,and one can directly transmit power through mechanical linkages and solve the purpose.
But,it is the versatility of the hydraulic system which has made it so popular now a days.
ADVANTAGES OF A HYDRAULIC POWER TRANSFER :-
The advantages of hydraulic system are.
1. Reversibility :-Only few prime movers are reversible.And for the reversible operation they need to be completely stopped or slowed,But in case of hydraulic system it can be versed in full motion with out damage.A directional valve or a reversible pump gives the reversible control and a relief valve protects the system from overload.
2. Variable speed:-Most of the prime movers are desired to run at constant speed but we need our actuator to run at variable speed.In hydraulic system has a advantage that the actuator can be driven at variable speed by controling the delivery of pump by a flow control valve.
3. Overload protection :-In hydraulic systems we have pressure relief valve which protects the system from overload damage.
4. System can be easily stalled:- An electric motor can not be stalled without blowing a fuse or an engine can not be stalled without a requirement for restarting it.But ahydraulic system can be stalled while the system is running by just bypassing the flow to the reservoir. It again works automatically when the system overload is reduced.
5. Very compact packages :- hydraulic system is very compact and easy to handle and mount in the system.
The name hydraulics in fact comes from Greek word ,HYDRO means Water and AULOS means pipe.
The hydraulic power transmission is instant because the transfer medium is fluid which is incompressible or very slightly compressible.some of the hydraulic presses use water as the medium but normally in power hydraulics we use petroleum oil because of its lubricating ability and very slight compressibility. Even in 1000 psi it will only compress about 0.5 % of its volume is not it great.
HOW PRESSURE IS CREATED ?
It is a common thinking that pressure is created by the pump and pump is always blamed for the pressure problems but it is not true.
***pump never creates pressure it only creates a flow.The restriction to the flow creates the pressure.
For example if the system has no load or no friction then the pressure gauge fitted in the system will show zero pressure.It means the pump will deliver the same amount of flow regardless the pressure.
for example in the above figure the pressure in the system is force per unit area i.e 8000 lb/10 square inch = 800 psi.If there is a leakage in the system then also the pressure is 800 psi.A leakage in the system only decrease the efficiency of the pump but not the pressure.
Hence any restriction to the flow of fluid creates the pressure like an orifice or a load or friction in the pipe in which the flow is occurring.The inherent property of fluid is to follow the least resistance path.If the flow is occurring in a parallel flow path then the pressure in the system will show same as the pressure created by the least resistance flow path.
But in case of series of resistance the pressure before the first resistance will be same as the sum of all the resistance in the path to be followed and so on.
SOME OF THE TERMS AND FORMULAE RELATED OF HYDRAULIC COMPONENTS :
1. FORCE IS PROPORTIONAL TO PRESSURE AND AREA.
F = P * A
F = APPLIED FORCE (POUND OR lb)
A= NORMAL AREA IN CONTACT WITH THE FORCE (INCH SQUARE)
P= THE PRESSURE (POUND PER SQUARE INCH)
2. SPEED OF AN ACTUATOR DEPENDS ON THE CYLINDER SIZE AND THE RATE OF FLOW IN TO IT.
SPEED = (VOLUME/ TIME) / AREA
3. VELOCITY OF FLOW IN PIPES VARIES INVERSELY AS SQUARE OF INSIDE DIAMETER OF THE PIPE.USUALLY FRICTION OF FLUID FLOWING THROUGH PIPE IS PROPORTIONAL TO VELOCITY BUT IN CASE OF TURBULENT FLOW IT VARIES AS THE SQUARE OF IT'S VELOCITY.
4. IF THE FLOW GPM (GALLON PER MINUTE) AND VELOCITY(FEET PER SECOND) ARE KNOWN THEN USE THIS RELATIONSHIP TO FINE THE CROSS SECTIONAL AREA OF THE PIPE.
AREA = (GPM * 0.3208)/ VELOCITY IN FEET PER SECOND.
AREA = (LPM * 16667 )/ VELOCITY IN MM PER SECOND.
=> VELOCITY = GPM/(3.117 *AREA IN INCH SQUARE)
=> VELOCITY = LPM /(16667 * AREA IN MM SQUARE)
5. POWER = (FORCE * DISTANCE) / TIME
UNIT OF POWER IS HORSE POWER .ONE HORSE POWER OR hp IS EQUIVALENT TO 33000 lb LIFTED IN ONE MINUTE TO ONE FEET HEIGHT.
=> 1 hp = 33,000 lb feet /min = 550 lb ft / sec
1 watt = 1 N m /sec
=> 1 hp = 746 watt
IN HYDRAULIC SYSTEM POWER IS EQUAL TO
POWER = FLOW * PRESSURE
=>POWER = GPM * (POUNDS / SQ INCH )
=> HORSE POWER (hp) = GPM * PSI * 0.0007
=> KILOWATT = LPM * BAR * 0.002
6. HP = (TORQUE * RPM ) / 63025
KILOWATT = (TORQUE * RPM) / 9550
to be continued..........................................
learn and enjoy.....
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