Industrial Hydraulic Systems

7/28/2019 Industrial Hydraulic Systems

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6/18/2013Welcome to the World of Fluid Power1

Industrial Hydraulic Systems


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Introduction

Hydraulics is a part of Fluid Power &Motion Control

Hydraulic Systems are robust, accurate,user friendly but complicated

Keeping the Hydraulic Systems inrestoration is only possible through

knowledge and skill.


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Agenda

We will be covering the basic threeaspects namelyEnergy Input, Energy

Control & Energy Output. We will learn about all the three aspects as

mentioned above through explanation ofPrinciples involved in hydraulic controltechnology using colored pens & whiteboard.


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Programme Objectives

To understand basic principles of Hydraulics. To learn & understand the hydraulic graphic

symbols.

To understand Hydrodynamic & Hydrostatic

Pumps.

To understand & learn about hydraulic controlvalve technology.

To understand hydraulic Loads & their application To learn how to analyze hydraulic circuits.

To understand & grasp the methods of HydraulicSystem Troubleshooting & Condition Monitoring.


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Vocabulary

We will be working with the following terms -Q - Flow Rate

P - System Pressure

F - Force

A - Effective Area

V - Volume

v - Velocity

P - Pressure DifferentialT - Temperature Differential


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Vocabulary

F

A P

Relationship between Force

(lbsf), Pressure (psi) and

Area (in2

)

Relationship between Pump

Volume (GPM), Velocity

(in/Sec) and Cylinder Area(in2)

Q

v A


7/586/18/2013Welcome to the World of Fluid Power7

Flow & Flow Rate

1. Open Channel Flow

2. Confined Flow

Why Flow takes place

Flow takes place from higher region to lower region

Flow takes place from higher pressure to lower pressure

Flow through any restriction is a function ofpressure drop across it (P).


8/586/18/2013Welcome to the World of Fluid Power

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Open Channel Flow

If a river is flowing from a higher level to lower levelthen flow is taking place in an open area.

Flowing (falling)

water can cause awheel to rotate, open

channel hydraulic

energy is converted

into mechanical

energy

Flowing (falling) water can

cause a wheel to rotate,

open channel hydraulic

energy isconverted into

mechanical energy



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Flow Through Pipes

We have seen that it is possible to convert energy inthe flowing water into Mechanical energy.

The reverse is also possiblewhich means that

Mechanical energy can be converted into flowingWater (Hydraulic energy)

But before we understand how it is possible to make the

Water (liquid) to flow from lower level to higher level,

let us understand few basic principles ------------



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Flow through a pipe can be in two states, namely

Laminar Flow & Turbulent Flow

If fluid particles are moving in parallel lines then it is

said to be Laminar flow

If the fluid particles are moving in a random path then itis said to be a Turbulent flow

Laminar Flow Turbulent Flow

Flow ConditionsLaminar Flow & Turbulent Flow

Flow Graph



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Kinetic Energy & Potential Energy

Kinetic Energy:

Kinetic Energy is in the form of Fluid velocity & Fluid weight.

Potential Energy:

Potential energy is available in the form of Pressure

Bernoullis Theorem:

V2 P

2 +

gh+ =

Constant

where:v= fluid velocity along the streamline

g= acceleration due to gravity

h = height of the fluid

p = pressure along the streamline

= density of the fluid
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Equation of continuity

Fluid dynamics explains that acontinuity equationis an

equation of conservation of mass

What comes in same goes out -

The law of conservation of mass/matter, also known as law of

mass/matter conservation, states that the mass of a closed system,

will remain constant, regardless of the processes acting inside the

system. An equivalent statement is that matter cannot be

created/destroyed, although it may be rearranged.



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What is Pressure?Mathematically explained pressure is force per unit

Area, it is measured either in Lbs/in2 or Kg/cm2 but why

Pressure is created & what causes the pressure to rise?

Whenever free flow is not allowed then smallest entities try to

escape by force and in this process pressure is created if the

number of entities are large in number & every one is applying

force, pressure tend to rise


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What is Atmospheric Pressure?

The Planet Earth

where we live is

surrounded by a

bubble of Air, which

is spreading up to 30

mile all around

30 milesThe air particles are having weight

and due to gravitational force thisbecomes force, this force at sea level

is around 14.7 lbs/in2 (PSI) or 1.013

Kg/cm2 (BAR)

This pressure on the surface of Earthis known as Atmospheric Pressure.

How to measure any increasing or decreasing pressure on earth?

For the measurement of quantities we need a Zero reference but sinceon Earth we live under atmospheric pressure we are not having a Zero

reference. Beyond the limits of earth's atmosphere there is no air thus

there in no pressure, so no air is our reference, that is Absolute zero.


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Two Measuring Scales are existing

1. Absolute scale

2. Relative scale

Relative Scale Absolute Scale

0 Absolute

Gauge pressure 0

Vacuum Scale


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Hydraulic Pumps

1. Hydrodynamic

2. Hydrostatic

Hydrodynamic Pump:

Hydrodynamic Pumps are Non-positive displacement pumps, thesepumps provide continuous flow and there application is only limited

to fluid transfer.

Hydrostatic Pumps:

Hydrostatic Pumps are Positive displacement pumps, these pumps

provide pulsetic flow and their application is basically in the area of

Hydraulic Systems


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Hydrodynamic Pumps

Atmospheric Pressure

14.7 psi or 1.013 Bar

Volute Path Path

Hydrodynamic Pump:

A Centrifugal Pump falls under

the category of Hydrodynamic,

this pump provides flow by

virtue of its own construction,

if we carefully observe the

casing is volute in itsconstruction and this is the

reason that Velocity Head gets

converted into Pressure Head

at its outlet.These pumps are basically

Transfer Pumps and provide

continuous flow.


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Hydrostatic Pumps

500 RPM

Swept Volume of Cylinder = 10 cm3

Hydrostatic Pumps are positive displacement pumps, these

pumps are pulsetic in nature.Positive displacement pumps are used in Hydraulic Systems

Pump Size = Cubic Centimeter per Minute

Or Cubic Inches per Minute

LPM =

GPM =

CCR X RPM

1000

CIR X RPM

231


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Pump Specifications

Pump Type

Pump Rated Pressure

Pump Size

Pump RPM

Pump Volumetric Efficiency

Pump Mechanical Efficiency

Pump Overall Efficiency


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Types of PumpsPositive Displacement Pumps

Gear Pumps Vane Pumps Piston Pumps

External Gear Pump Internal Gear Pumps

Spur Gear Type Internal Gear Mesh

Lobe Type Gerator Pump

Screw Pumps

Balanced Unbalanced

Vane Pump Vane Pump

Axial Piston Radial Piston

Pumps Pumps

Axial Inline

Bent Axis

Fixed Displacement Pumps Variable Displacement pumps


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External Gear Pump

A Gear pump uses the meshing of

gears to pump fluid by displacement.

They are one of the most common

types ofpumps for hydraulic fluid

power applications.

There are two main variations;

external gear pumpswhich use two

external spur gears, and internal gear

pumpswhich use an external and an

internal spur gear.

Gear pumps are f ixed displacement, meaning they pump a constant

amount of fluid for each revolution.
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Internal Gear Pumps

Internal gear (Gerotor) pump design for automotive oil

pumps.

Internal gear (Gerotor) pump design for automotive oil

pumps.

A Gerotor is a positive displacement pumping unit. The

name gerotor is derived from "Generated Rotor". A Gerotor

unit consists of an inner and outer rotor.
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Axial Inline Piston Pump

Axial Piston Pumps are variable displacement pumps.

The pistons in an axial piston pump reciprocate parallel to the

centerline of the drive shaft of the piston block. That is, rotary shaftmotion is converted into axial reciprocating motion. Most axial

piston pumps are multi-piston and use check valves or port plates to

direct liquid flow from inlet to discharge.

Axial Piston Pumps can be

variable displacement and

pressure compensated to

match their Power with therequired Load power


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Pump CharacteristicsPump Rated Pressure

It is that load pressure up to which a pump can handle the loadand beyond which there is a possibility that the pump might fail.

Pump Size

Pump Size is always given in CIR/CCR or LPM/GPM.

Pump RPM

Pump RPM is always given by the Manufacturer and it normally

lies between 1250 to 1850 until & unless it is specified.

Pump Volumetric Efficiency

Volumetric efficiency is obtained by dividing Actual flow rate by

the Theoretical flow rate


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Pump Mechanical Efficiency

Pump Overall Efficiency

Mechanical efficiency is obtained by dividing Actual Torque by

the Theoretical Torque.

Torque in (lbs inch) =Pressure in psi X CIR (cubic inches per revolution)

2

Overall Efficiency = Volumetric Eff. x Mechanical E

ff

=Output Horse Power

Input Horse PowerX 100


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Pump Horse Power

Let us define Horse Power: Rate of doing work

If we explain rate of doing work we will have to go to First Principle -

Distance tobemoved 1

foot in

1 Second550lbs

1 Horse Power = 550 ft lbs/sec (This is the basic value of 1 HP)In other words we can define it in the following form

Horse Power = Force x Distance Moved per Unit time

B i H d li Ci it


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Basic Hydraulic Circuit

Effective Area

Load

Annulus Area

What is Working Pressure?

What is Max. System Pressure?

M1

2

3


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Hydraulic Graphic Symbols

A Firm & thick line is called Working Energy Line

A long dash line is known as Control Energy Line orPilot Line

A short dash line is known as Leak Line orDrain Line

Circles Triangle Filled Triangle Not Filled

Circles are used for Ball Triangles are used for Hydraulic Energy

Puppet, Energy Source, Flow Direction and Pneumatic Energy

Pump Body Flow Direction

Flow Envelop Flow Path Varying Parameter Spring Varying

Spring Force

Fluid Conditioner Thermometer Compensation Bi-directional Flow


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Pressure Control ValvesPressure Control Valves are very important elements in any Hydraulic

Circuit, without these valves we cant achieve correct pressure control in

different areas of control, following is a list of different types of PressureControl Valves

1. Pressure Relief Valve 5. Charge Valve

2. Pressure Reducing Valve 6. Brake Valve3. Sequence Valve 7. Unloading Valve

4. Counter Balance Valve 8. Crossover Relief Valve

THREE Types of pressure control valves are available from Technologypoint of view.

1. Spool Types 2. Simple Poppet Types

3. Cartridge Types


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Hydraulic Control Valves

Hydraulic Control Valves are developed over a long period of time in

two directions and categories

1. Spool Valves

2. Poppet Valves

Spool Valves provide Multiple Flow Paths, they are Pressure Balanced

but they leak between Housing and the Spool.

Poppet Valves provide Single Flow Path, They are digital in nature but

they provide Leak Proof conditions.

Both of theses categories are having advantages and disadvantages but

combined together they solve many problems.

P R li f V l


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Pressure Relief Valves

Pressure Relief Valves are of three Types

1. Directly Operated Pressure Relief Valve

2. Pilot Operated Pressure Relief Valve

3. Pump Unloading Valve

4. Pilot Operated Pressure Relief Cum Unloading Valve

Basic Features of Pressure Relief Valve

Normally Closed

Pressure is sensed internally at inlet port

Variable Pressure Control

Internally Drained


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Directly Operated Pressure Relief Valve

Directly Operated Pressure Relief valves are quick acting in nature

but these valves suffer from a drawback of large Pressure Override.These valves work alright with small volumetric flow Pumps but

these valves can not be used with large volumetric flow Pumps.

Unloading Valve


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Unloading Valve

While hydraulic system is

in idling condition then

Relief Valve is opening &closing to keep the system

pressure at relief valve

setting but in this process

the pump energy is usedand this is a loss, which is

converted to thermal

energy, which can cause

the oil temperature to rise

but by using an Unloadingvalve this situation can be

avoided.

Pilot Operated Pressure Relief Valve


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Pilot Operated Pressure Relief Valve

Directly operated pressure relief valves can only be used with 25 LPM

pumps and not beyond. For higher LPM pumps Pilot Operated pressurerelief valves are used.

Main Valve

Pilot Valve

Pilot Operated Pressure Relief cum Unloading Valve


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Pilot Operated Pressure Relief cum Unloading Valve

It is important to note that a separate Unloading valve will be a real

nuisance for the circuit designer more over it is essential to interface

the mechanical hardware with digital systems, so a single valve is

developed to take care of all the needs.

A Pilot Operated Pressure Relief cum Unloading valve is the most

important valve in the modern Hydraulic Systems.

Main Valve

Pilot Valve

Pressure Reducing Valve


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6/18/2013Welcome to the World of Fluid Power 36

Pressure Reducing ValvePressure Reducing Valves are also important hydraulic elements

which are used to control the pressure as per the requirement in a

branch circuit

Features of Pressure Reducing Valve

Normally Open

Pressure sensed internally at

outlet port

Variable Pressure Control Externally drained

Externally Drained

P S V l


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Pressure Sequence Valve

Externally Drained

Hydraulic Pressure Sequencing

Valves are also very important

elements, since pressure sensing

control is quite accurate Designer

may consider to use a Pressure

Sequencing valve in the Hydraulic

circuit.

B k V l


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Brake Valve

Brake Valve is used to stop a

single direction Hydromotor

instantly without increasing

excessive pressure and also

protecting motors fromcavitation.

These valves are very

effective and easy to adjust

for all kind of Loads.

Hydraulic Loads


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Hydraulic Loads

There are three types of Hydraulic Loads

1. Resistive Loads

2. Overrunning Loads

3. Inertial Loads

Load

Hydraulic Force Load ReactionResistive Load

When Load reaction is

opposite to Hydraulic

Force then it is calledresistive load.

O i L d


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Hydraulic Force Load Reaction

Overrunning Load

Load

When Load Reaction is in the same direction as that of the Hydraulic

Force then it is called Overrunning Load

Counter Balance Valve


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Hydraulic Force Load Reaction

Counter Balance Valve is a

hydraulic control elementwhich is required to handle

heavy loads which are moved

down wards, this valve

provide support to bring theload down very smoothly and

at a required velocity to get

good control over load inertia

and acceleration due to

gravitation (g).



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Inertial Load

When load is accelerating ordecelerating under both of these

conditions load reaction opposes the

Hydraulic force then it is called

Inertial Load.

While a Hydraulic Motor is rotating

a heavy load in both directions then

the motor is handling Inertial Load,

the motor requires protectivecircuits.

Cross Over

Relief Valve

Direction Control Valves


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Direction Control Valves

Direction Control Valves are the control elements which provide

movement to the Linear as well as Rotary actuators. In doing so theyprovide to actuators START, STOP & CHANGE of DIRECTION

functions in every Hydraulic Circuit.

Direction Control Valves can be divided into following categories

1. Spool Valves

2. Cartridge Valves

Functional Classification of DC Valves

1. Valve Body with Spool/Poppet

2. Valve Operating System

DC Valves can be Operated by the following means


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p y g

1. Manual Operation

2. Mechanical Operation

3. Hydraulic Operation

4. Pneumatic Operation

5. Electrical Operation

DC Valves (Spool Valves)


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DC Valves (Spool Valves)

DC Valves are further classified by their number of positions and their

center configuration

1. Two Position Valves

2. Three Position Valves

21

21 3

P T

A B

DC Valve Spool Design


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DC Valve Spool Design

Spool edges play an important role in controlling the fluid and that iswhy these edges are called controlling edges.

Imagine that a spool is opening to provide flow, if this opening is sudden

then NO-flow to FULL-flow or FULL Flow to NO Flow condition will

appear quickly and this will cause a pressure shock (Pressure Surge).

Pressure Shock= 3 to 4 times of Working Pressure

Pressure shock can cause Seal failure, Pressure Gauge & Fitting Failure.

Spool Land Groove

P


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t

P

Set Value

Time for which PS appeared

We can clearly observe that the pressure shock rises over and above theworking pressure, taking this into consideration we must control the

sudden rising pressure, the control is dependant on the following two

factors

1. Geometry of the Control Edge

2. Shift Speed of the Spool

Pressure Surge

How to Reduce the Magnitude of the Pressure Surge


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T A P B T

ow o educe e g ude o e essu e Su ge

It is possible to reduce the effect of pressure surge by introducing the V-

Shape grooves on the periphery of the Control Edge of the Spool and by

limiting the shift speed of the spool itself.

What actually we are trying is to increase the flow rate gradually

between the two Ports by increasing the spool opening slowly thus

accelerating the load in a controlled manner.

Direction Control Valve in a Circuit


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Using a 2/2 Solenoid operated DC valve

we can achieve a digital control of a

Hydraulic cylinder.

Four numbers of 2/2 solenoid operated

valves are arranged in a fashion as shown

in the figure, now switching through

electrical current is possible by a PLC to

provide a precise digital control

Arranging digital valves into a hydraulic integrated circuit allows them toaccomplish the same functions as discrete spool-type valves while

retaining the advantages of digital valves.


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Direction control through a 4/3

Solenoid operated, Center Closed

DC Valve.

This particular valve is a multi-flow

path valve with two solenoids to

provide forward and reverse

movement of the cylinder, unlike

the previous example in which

digital functions are possible with

Four solenoids.

Advantage:

Single hardware element

Easy to maintain


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A single DC valve with one

Sequence valve can control Two

Cylinders in a sequence.This circuit does not solve the

problem of controlling the pressure

of a branch circuit. That means if

cylinder one is to be operated athigher pressure and cylinder two is

to be operated at much lower

pressure then it would not be

possible by this circuit

Controlling Branch Pressure


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Controlling Branch Pressure

By introducing a pressure

reducing valve we can easily

control the branch pressure,

because a reducing valve willclose whenever require

pressure is reached in the

branch.

Flow Control Valves


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Flow Control Valves

Flow-control valves include simple orifices to sophisticated closed-

loop electrohydraulic valves that automatically adjust to variations

in pressure and temperature.

The purpose of flow control in a

hydraulic system is to regulate

speed.

All the devices discussed here

control the speed of an actuator by

regulating the flow rate.

Flow rate also determines rate ofenergy transfer at any given

pressure.


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The two are related in that the actuator force multiplied by the

distance through which it moves (stroke) equals the work done on

the load.

The energy transferred must also equal the work done. Actuator

speed determines the rate of energy transfer (i.e., horsepower), and

speed is thus a function of flow rate.

Directional control, on the other hand, does not deal primarily with

energy control, but rather with directing the energy transfer systemto the proper place in the system at the proper time.

Diff t T f Fl t


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Different Types of Flow measurement

Controlling flow of a fluid-power system does not necessarily meanregulating volume per unit of time from a valve.

Flow rate can be specified in three different ways, so it is important

to be aware of how flow is to be specified or measured:

1. Volumetric flow rate (Qv)

2. Weight flow rate(Qw)

3. Mass flow rate (Qg)

Control of Flow Rate with Valves


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There are eight types of flow-control valves:

Orifices - A simple orifice in the line,

Figure 1(a), is the most elementarymethod for controlling flow.

Fig. 1. Simple fixed orifice (a) and

variable orifice (b) flow controls.

Flow regulators - This device, Figure

2, which is slightly more sophisticated

than a fixed orifice, consists of an

orifice that senses flow rate as a

pressure drop across the orifice; a

compensating piston adjusts to

variations in inlet and outlet pressures.

Bypass flow regulators - In this flow


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yp g

regulator, flow in excess of set flow rate

returns to reservoir through a bypass port,

Figure 3. Flow rate is controlled by

throttling fluid across a variable orificeregulated by the compensator piston. The

bypass flow regulator is more efficient

than a standard flow regulator.

Demand-compensated flow controls -

Flow controls can also bypass excess

system flow to a secondary circuit, Figure

4. Fluid is routed at a controlled flow rate

to the primary circuit, and bypass fluidcan be used for work functions in

secondary circuits without affecting the

primary one.

Pressure-compensated, variable flow


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valves - This flow control is equipped with anadjustable variable orifice placed in series with

a compensator. The compensator automatically

adjusts to varying inlet and load pressures,

maintaining an essentially constant flow rate

under these operating conditions to accuracies

of 3% to 5%, Figure 5. .

Pressure- and temperature-compensated,

variable flow valves - Because the viscosity ofhydraulic oil varies with temperature (as do the

clearances between a valve's moving parts),

output of a flow-control valve may tend to drift

with temperature changes. To offset the effects

of such temperature variations, temperature

compensators adjust the control orifice openings

to correct the effects of viscosity changes

caused by temperature fluctuations of the fluid,

Figure 6.

Documents

Industrial Hydraulic Systems