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AGE 221 FLUID POWER

VALVES FOR FLUID POWERSYSTEMS

Principle Types of Valves

PRESSURE FLOW DIRECTION

CONTROL VALVES

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Orifice Equation

Q C Ag p

o or

= 2 D

r

CC00 is determined experimentally is determined experimentallyPressure drop is proportional to flowPressure drop is proportional to flowValve Principles: Area is a adjusted to Valve Principles: Area is a adjusted to control pressure and flow ratecontrol pressure and flow rateDensity of petroleum-based fluids 850-950 kg/mDensity of petroleum-based fluids 850-950 kg/m33

Flow Through an Orifice

Laminar Flow Through an OrificeLaminar Flow Through an Orifice

Turbulent Flow Through an OrificeTurbulent Flow Through an Orifice

333

Homework

ppiippoo

ppxxAAmm

AAmm

zz Solve problem 3.13 a, b, and c in the text.Solve problem 3.13 a, b, and c in the text.

Directional Control ValvesDirectional Control Valves

z Checkz Two wayz Three wayz Four Wayz Proportional

444

JIC Directional Valve Envelope

Ports and Way

z Ports are the tubing connections for the valve.z The way refers to the path of fluid flow

555

Check Valve

A check valve has two ports andA check valve has two ports andone way flow.one way flow.

Two Way Valves

A two-way valve has two ports;and allows flow in two directions

Two way, Two Position, Two way, Two Position, two port, normally closedtwo port, normally closed

666

Three-way Valves

z A three-way valve pressurizes andexhausts fluid through one port.

z A three-way valve has two other ports forthe supply and return fluid.

Three way, two position, Three way, two position, three portthree port

Four Way Valves

z A four-way valve pressurizes and exhauststwo ports.

z It can have more that four actual portconnections for supply, exhaust, and twooutlet ports.

777

Methods of Control

Lever Actuated Open-Center DCV

888

Solenoid Actuated Closed CenterDCV

Lets Try an Example

Modify the design of this basic circuit with a the solenoid activatedModify the design of this basic circuit with a the solenoid activatedDCV on the previous slide so that the motor can turn in both directionsDCV on the previous slide so that the motor can turn in both directionsand normally is stopped. Which parts of the circuit are at systemand normally is stopped. Which parts of the circuit are at systempressure for the different modes of operation?pressure for the different modes of operation?

999

PRESSURE CONTROL VALVUES

z Pressure Relief, Pressure Reducing Valvesy To limit or reduce pressure

z Sequence Valvesy To sequence hydraulic operations

z Unloading Valvesy To unload the pump during slack cycles

z Counterbalancey To hold a load

Pressure Relief

z To limit or reduce pressurez Direct Acting or Pilot Operated

101010

Direct Acting Pressure Relief

To ReservoirTo Reservoir

System PressureSystem Pressure

Direct Acting Pressure Relief



111111

Pilot Operated Pressure Relief



Pressure Pressure PortPort

Light Light SpringSpring

Pilot Operated Pressure Relief



121212

Pressure Override in a Relief ValvePressure Override in a Relief Valve


Flow

thro

ugh R

elie

f V

alv

eFl

ow

thro

ugh R

elie

f V

alv

e

Direct Acting Relief ValveDirect Acting Relief Valve

Pilot OperatedPilot OperatedRelief ValveRelief Valve

Cracking PressureCracking Pressure

Full Flow PressureFull Flow Pressure

Unloading Valves

A common use of an unloading valve is to discharge the fluidA common use of an unloading valve is to discharge the fluidof a fixed displacement pump when it is not in use in a circuitof a fixed displacement pump when it is not in use in a circuit

An unloading valveAn unloading valveprovides power savings forprovides power savings fornon-working systemsnon-working systems

131313

Example

A fluid power system has a 10.54 cmA fluid power system has a 10.54 cm33/rev pump and a /rev pump and a rated speed of 1800 rpm. The system pressure relief valve rated speed of 1800 rpm. The system pressure relief valve is set for 10.3is set for 10.3 MPa MPa. When the system is idle, all oil is . When the system is idle, all oil is dumped to the reservoir over the pressure relief valve. dumped to the reservoir over the pressure relief valve. Is fluid power used when this circuit is inactive? If yes, Is fluid power used when this circuit is inactive? If yes, how much?how much?

Pressure Reducing Valves

Supply branch circuits with fluidSupply branch circuits with fluidat a lower pressure than systemat a lower pressure than systempressure.pressure.

141414

Sequence Valves

Control the order ofControl the order ofoperations in branchoperations in branchcircuitscircuits

Sequence Valve Operation

The sequence valve is normally closed. It is set to react to a system The sequence valve is normally closed. It is set to react to a system pressure less than the setting of the pressure relief valve.pressure less than the setting of the pressure relief valve.

151515

Sequence Valve Operation

Pressure increases resulting from an actuator reaching thePressure increases resulting from an actuator reaching theend of its stroke open the sequence valve.end of its stroke open the sequence valve.

Clamp-Drill Circuit

ClampClamp

161616

Counterbalance Valves

Direct PilotDirect Pilot

OptionalOptionalRemote PilotRemote Pilot

Unloading valve is set to 10% above the system pressure Unloading valve is set to 10% above the system pressure required to hold the load. required to hold the load.

Counterbalance ValvesCounterbalance Valves

Direct PilotDirect Pilot

Determine the unloading valve settingDetermine the unloading valve settingrequired to hold the load?required to hold the load?

9090 kN kN

300 cm300 cm22

150 cm150 cm22

171717

Answer

Pressure required to hold the load:Pressure required to hold the load:

MPap

p

cmkN

AF

621509010

10

==

=

Set the unloading valve for a 10% higher pressure:Set the unloading valve for a 10% higher pressure:

MPa6.6=p

Flow Control

z Fixed or Variablez Compensated

y for Pressure and Temperature

z Flow Divider

181818

Methods of Flow Control

z Meter-Iny By metering the fluid supplied to the actuator

z Meter Outy By metering the fluid returned from the

actuator

z Bleed-offy By bleeding the excess fluid off to the

reservoir

Meter-In Circuits

Flow control is between motor and actuatorFlow control is between motor and actuatorMeter-In Circuits can only be used with opposing loadsMeter-In Circuits can only be used with opposing loadsExcess flow goes across relief valve to the tankExcess flow goes across relief valve to the tank

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Meter-Out Circuits

Flow control is on the outlet side of the actuatorFlow control is on the outlet side of the actuatorWorks for opposing or non-opposing loadsWorks for opposing or non-opposing loadsExcess flow dumped across the relief valveExcess flow dumped across the relief valvePressure intensification is a concern in circuit between actuator Pressure intensification is a concern in circuit between actuator and valveand valve

Bleed-Off Circuits

Meter a portion of the flow directly to the reservoirMeter a portion of the flow directly to the reservoirSystem pressure determined by load, thus saves energySystem pressure determined by load, thus saves energyOnly works with opposing loadsOnly works with opposing loadsSomewhat unsteady actuator flow control, since metered Somewhat unsteady actuator flow control, since metered flow goes to reservoir.flow goes to reservoir.

202020

Flow Divider Valves

z Directs flow 2 or more circuitsz Controls flow...but also control direction.z Common on off-road equipment to divide

flow between circuits (e.g., powersteering and front-end load or left andright crawler tracks)

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