Fluid Power Systems Fluid Power Systems

Mill Creek High SchoolMill Creek High School

Power and EnergyPower and Energy

ObjectivesObjectives

Identify differences between hydraulic and Identify differences between hydraulic and pneumatic systemspneumatic systems

Identify advantages of fluid power systemsIdentify advantages of fluid power systems Understand uses of valves in FPSUnderstand uses of valves in FPS State physical characteristics of liquids in State physical characteristics of liquids in

FPSFPS Understand why hydraulic cylinders can Understand why hydraulic cylinders can

increase mechanical advantageincrease mechanical advantage

ObjectivesObjectives

Discuss examples of various applications Discuss examples of various applications of FPSof FPS

Understand difference between gauge and Understand difference between gauge and actual pressureactual pressure

Summarize differences between single Summarize differences between single and double acting cylindersand double acting cylinders

Interpret a basic Fluid Power CircuitInterpret a basic Fluid Power Circuit Calculate Mech. Advantage created using Calculate Mech. Advantage created using

liquids under pressure.liquids under pressure.

Hydraulic SystemHydraulic System

A system that controls and transmits A system that controls and transmits energy through the use of liquidsenergy through the use of liquids Hydraulic oilHydraulic oil Uses cylinders, pumps and linesUses cylinders, pumps and lines

Pneumatic SystemPneumatic System

Similar to Hydraulic but GASSES are used Similar to Hydraulic but GASSES are used instead of liquidsinstead of liquids Air is most commonly usedAir is most commonly used Similar in properties to liquid but has some Similar in properties to liquid but has some

differencesdifferences

Why Fluid PowerWhy Fluid Power

The ability to multiply force in order to The ability to multiply force in order to generate strengthgenerate strength

Less wear than other types of systemsLess wear than other types of systems Almost unlimited power can be producedAlmost unlimited power can be produced Can transfer power over great distanceCan transfer power over great distance Easy to complete and maintainEasy to complete and maintain Gasses (pneumatics) offer cushioning to Gasses (pneumatics) offer cushioning to

shockshock

Physics of Fluid Power SystemsPhysics of Fluid Power Systems

Fluids take the shape of the container they Fluids take the shape of the container they are inare in

Fluids exert pressureFluids exert pressure Fluids can freely flow from one container Fluids can freely flow from one container

to anotherto another

Fluids Exert PressureFluids Exert Pressure

Pressure is exerted in ALL directions Pressure is exerted in ALL directions equallyequally NOT only on the bottoms of the containerNOT only on the bottoms of the container

There is more pressure on the lower sides There is more pressure on the lower sides because pressure is a product of weightbecause pressure is a product of weight

How Fluids ActHow Fluids Act

Fluids flow from Fluids flow from higher elevation to higher elevation to lower elevation until lower elevation until they are equalthey are equal

Fluids will flow until Fluids will flow until both pressures in both pressures in both areas are equalboth areas are equal

Effort and RateEffort and Rate

Pressure gauge: measures difference Pressure gauge: measures difference between outside and inside pressurebetween outside and inside pressure

Measured in Pounds-per-square-inch (psi)Measured in Pounds-per-square-inch (psi) ““psi” is the effort in the systempsi” is the effort in the system Flowmeter: measures in gallons-per-Flowmeter: measures in gallons-per-

minute (GPM) or cubic-feet-per-minute minute (GPM) or cubic-feet-per-minute (CFM)(CFM)

““GPM” or “CFM” is the RATE in the GPM” or “CFM” is the RATE in the systemsystem

PSIG vs PSIAPSIG vs PSIA

PSIG-pounds per square inch gaugePSIG-pounds per square inch gauge The difference between circuit pressure and The difference between circuit pressure and

atmospheric pressureatmospheric pressure Most commonly usedMost commonly used

PSIA-pounds per square inch actualPSIA-pounds per square inch actual Accounts for atmospheric pressureAccounts for atmospheric pressure 200psig=214.7psia at sea level200psig=214.7psia at sea level

What would psig be in Denver, COWhat would psig be in Denver, CO Would psia be higher or lower in Denver. Would psia be higher or lower in Denver.

COCO

Viscosity of LiquidsViscosity of Liquids

Viscosity: is a measurement of internal Viscosity: is a measurement of internal friction of a liquid (resistance to flow)friction of a liquid (resistance to flow)

This is molecularThis is molecular Higher the viscosity rating the slower a Higher the viscosity rating the slower a

liquid will flowliquid will flow How long it takes a quart of substance to How long it takes a quart of substance to

flow through a specific size opening at a flow through a specific size opening at a specific temperaturespecific temperature

Opposition to FlowOpposition to Flow

Friction: occurs between the substance Friction: occurs between the substance and the pipe, hose or fitting.and the pipe, hose or fitting.

Turbulence: Occurs within the liquid itselfTurbulence: Occurs within the liquid itself Laminar Flow: stratified layers of motion Laminar Flow: stratified layers of motion

flow smoothly over one another.flow smoothly over one another. At junctions or “t” fittings they become At junctions or “t” fittings they become

intermixed and all slow down (turbulence)intermixed and all slow down (turbulence)

Hydraulic PumpsHydraulic Pumps

Hydraulic pumps: Hydraulic pumps: supply and transmit supply and transmit pressure needed to pressure needed to system…Convert system…Convert mechanical energy to mechanical energy to fluid powerfluid power Gear pumps: pump in Gear pumps: pump in

which two gears mesh which two gears mesh together inside a together inside a housinghousing

Hydraulic PumpsHydraulic Pumps

Reciprocating pumps: Reciprocating pumps: use a piston that use a piston that moves back and forth moves back and forth (reciprocates) to (reciprocates) to move hydraulic fluidmove hydraulic fluid Check valves keep Check valves keep

fluid from moving fluid from moving backwardsbackwards

Hydraulic PumpsHydraulic Pumps Centrifugal pumps: use centrifugal force to Centrifugal pumps: use centrifugal force to

move fluids in a systemmove fluids in a system Centrifugal force makes objects fly Centrifugal force makes objects fly

outward when spinning aroundoutward when spinning around Impeller: has many small blades and a Impeller: has many small blades and a

central inlet …it central inlet …it

draws the liquid out draws the liquid out

from centerfrom center

Controlling Fluid PowerControlling Fluid Power

Flow control valves: (aka: variable flow Flow control valves: (aka: variable flow restrictor)restrictor) can be used to control the output speed of the can be used to control the output speed of the

fluidfluid Pressure control valves: Pressure control valves:

Pressure reducing valves: reduce pressurePressure reducing valves: reduce pressure Pressure regulating valves: allow you to Pressure regulating valves: allow you to

adjust pressure coming from compressoradjust pressure coming from compressor

Controlling Fluid PowerControlling Fluid Power

Pressure Relief Valves: used to ensure Pressure Relief Valves: used to ensure that pressure in system does not get too that pressure in system does not get too high.high.

Directional Control Valves: (aka: spool Directional Control Valves: (aka: spool valve) to control which path the fluid takesvalve) to control which path the fluid takes

Transmitting Fluid PowerTransmitting Fluid Power

Through devices known as conductorsThrough devices known as conductors Hoses and pipes allow high pressure and Hoses and pipes allow high pressure and

tremendous movementtremendous movement Hoses flex to absorb shockHoses flex to absorb shock Pipes may require accumulator for absorbing Pipes may require accumulator for absorbing

shockshock

Sizing Fluid PowerSizing Fluid Power

Factor:Factor: Volume that conductor can carryVolume that conductor can carry Velocity at which it can travelVelocity at which it can travel Pressure the conductor is designed to handlePressure the conductor is designed to handle

Flow RateFlow Rate

Flow rate capacity is determined by the Flow rate capacity is determined by the inside diameter of the conductorinside diameter of the conductor

Slight increases in diameter increase the Slight increases in diameter increase the flow rate tremendouslyflow rate tremendously

A 1” diameter garden hose has 4X the flow A 1” diameter garden hose has 4X the flow rate of a ½” diameter hoserate of a ½” diameter hose

VelocityVelocity

The rate of motion in a particular directionThe rate of motion in a particular direction Typically measured in Feet-per-second Typically measured in Feet-per-second

(fps)(fps) As the surface area of the inside of a As the surface area of the inside of a

conductor increases the flow rate conductor increases the flow rate decreases because it can hold moredecreases because it can hold more

Helen GAHelen GA

PressurePressure

Working pressure: normal operating Working pressure: normal operating pressure that the conductor is designed to pressure that the conductor is designed to handlehandle

Test pressure: maximum pressure that the Test pressure: maximum pressure that the conductor is designed to withstandconductor is designed to withstand

Burst pressure: the pressure at which the Burst pressure: the pressure at which the conductor will burstconductor will burst

Must anticipate intermittent pressureMust anticipate intermittent pressure

Making Fluid Power WorkMaking Fluid Power Work

Actuators: device that converts fluid power Actuators: device that converts fluid power to mechanical powerto mechanical power

Single acting cylinder: force of fluid moves Single acting cylinder: force of fluid moves piston in one direction (Returned by load)piston in one direction (Returned by load)

Double acting cylinder: Force of fluid can Double acting cylinder: Force of fluid can move the piston in both directionsmove the piston in both directions

Making Fluid Power WorkMaking Fluid Power Work

Fluid motors: device Fluid motors: device that converts fluid that converts fluid power into rotary power into rotary mechanical motionmechanical motion Gear motor: Operate Gear motor: Operate

like a gear pumplike a gear pump Vane motor: fluid Vane motor: fluid

pushes against vanes pushes against vanes and higher pressure and higher pressure on one side spins iton one side spins it

Storing Fluid PressureStoring Fluid Pressure

Pressure tank: tank that stores air under Pressure tank: tank that stores air under pressure in a pneumatic systempressure in a pneumatic system

Accumulator: a device that stores Accumulator: a device that stores hydraulic liquid under pressure even when hydraulic liquid under pressure even when the pump is not running.the pump is not running. ABSABS

Blaise PascalBlaise Pascal

Pascal’s LawPascal’s Law

Area X Pressure = ForceArea X Pressure = Force

Of courseOf course

Area of the cross section of a Area of the cross section of a

cylinder = Pi * rcylinder = Pi * r22