2._HYDRAULICS.pdf

7/27/2019 2._HYDRAULICS.pdf

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HYDRAULICS

COMPONENTS IN

HYDRAULICS SYSTEM


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COMPONENTS


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COMPONENTS LAYOUT

Basic components:- Tank hold and cooling the hydraulic

oil.

Filterfiltering hydraulic oil from dirt.

Pumpsuck and distribute oilthroughout the system.

Accumulator - keep the systempressure, absorb vibration and stabilizethe system pressure.

Valve - regulate pressure in the circuitand control the direction of oil flow.

Cylinder produce power to do the

work for straight motion. Motor- produce power to do the work

for rotational movement.

CYLINDER

Direct controlled

valve

Relief valve

Motor

Tank

Filter

Check Valve

Accumulator

Pump

Flow control valve


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Baffles to SeparateReturn Line from Outlet Line

Magnetic Drain Plugsat Low Point(s)

Pump Inlet Line

Clean-outPlate

Return LineFilter

Large Surface Areafor Cooling

Fluid Level AbovePump Inlet

Capacity of 2-3Times Pump Flow

Filtered Breather Cap

Sight Gauge

Figure 5.2 Baffle plate controls direction of flow in tank

COPYRIGHT (2001) EATON CORPORATIONC

Tank


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1. a place to store hydraulic fluid2. Remove air trapped in the fluid

3. any sludge can be deposited

4. Accommodate any leakage in thesystem

5. Prepare the surface to cool the fluid.

Uses of Tank/Reservoir


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AtmosphericPressure

Inlet Phase Output Phase

Inlet

Outlet

to circuit to circuit

AtmosphericPressure

Inlet

Outlet

Figure 15-3 Positive displacement pumpCOPYRIGHT (2001) EATON CORPORATIONC

Pump


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Gear - cheap, durable, simple. Lessefficient, because they are constant(fixed) displacement, and mainly suitablefor pressures below 20 MPa (3000 psi).

Vane - cheap and simple, reliable. Goodfor higher-flow low-pressure output.

Piston - many designed with a variable

displacement mechanism, to vary outputflow for automatic control of pressure

Screw - used for high flows and relativelylow pressure (max 100 bar).

Types of hydraulics pump


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Inlet

Outlet

Idler Gear

Driven Gear

Volume on this sideincreases as gearteeth unmesh

Volume on this sidedecreases as gearteeth mesh

Figure 15-9 External gear pump


EXTERNAL GEAR PUMP


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INTERNAL GEAR PUMP


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IncreasingVolumeInlet side

DecreasingVolumeOutlet side

Figure 15-13 Eccentricity between rotor and cam ring


VANE PUMP


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Rotor

Vane

Cam Ring

Figure 15-12 Basic pumping elements of a vane pump


A rotary vane pump is a positive-displacement pump that consists

ofvanes mounted to a rotor that rotates inside of a cavity. In some

cases these vanes can be variable length and/or tensioned to

maintain contact with the walls as the pump rotates.


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SCREW PUMP

Screws pumps (fixed

displacement) are pump with

two screws used in one body.

The advantage of the screw

pumps is the low sound level

of these pumps; theefficiency is not that high.

The major problem of screw

pumps is the hydraulic

reaction forces which is

transmitted axially opposed

to the flow direction.


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Figure 15-41 Pump displacement is based on swash plate angleCOPYRIGHT (2001) EATON CORPORATIONC

StrokeStroke

OutletOutletOutlet

InletInletInlet

Stroke

PISTON PUMP
http://en.wikipedia.org/wiki/File:Swashplate_anim_metal.gif


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Piston pump have the advantage of being more

compact in design. The pumps are easier and more

economical to manufacture.

The disadvantage is that they are more sensitive to oil

contamination.


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Case Drain

Rotation

Outlet

Inlet

Swash Plate

Cylinder Block

PistonPre-Load Spring

Spherical Washer

Shoe Retractor Plate

Figure 15-32 An in-line piston pump



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Valve 5 Ways To Move the Valve


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Way To Control the Valve1. Non-Return /Check Valves

Check Valves are simply valves which provide reasonably

unrestricted flow in one direction and stop the flow in the otherdirection.

A light spring is generally used to retain the valve to a closed

position on near zero flow.


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19

Spring

OutletPort

InletPort

Check ValveSymbol

Poppet


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20

OutletPort

InletPort

Check ValveSymbol

Free Flow


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21

OutletPort

InletPort

Check ValveSymbol

No Flow


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2. Relief Valves Relief valves are generally spring loaded valves which include a

plug over a discharge port which is lifted against an spring force

if the system pressure exceeds a certain value This opens the flow to the discharge port relieving the pressure.

The pilot operated version enables more accurate control of the

setting and a lower relief setting can be accommodated


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3. Flow Control Valves The control of the flow is simply by restricting the flow such that the

pressure drop across the valve increases resulting in a reduced flow.

However for hydraulic systems based on positive displacement pump any

restriction in flow will cause a high rise in pressure which has to be limited byincluding a relief valve upstream of the flow control valve


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4. Directional Control Valves

Direction valves are the important hydraulic controls which

enable the motion of an actuator to be started, stopped andreversed.

There are three main types of directional control valves

- sliding-plate valves - rotational and linear.

- poppet valves

- spool valves.


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Figure 17-6 Bladder-type accumulatorCOPYRIGHT (2001) EATON CORPORATIONC

Gas Valve

Bladder

Shell

Port

Anti-ExtrusionValve

Nitrogen Gas

Accumulator


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Accumulator

An inert gas above the diaphragm is compressedwhen hydraulic fluid is forced into the space below the

diaphragm.

The compressed gas represents potential energy

that can be reconverted into hydraulic energy when

needed.For example, the stored energy can be used for emergency powering

of power brakes or power steering during engine failure.


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Figure 17-7 Bladder accumulator operation


psig0

500

1000

1500

2000

psig0

500

1000

1500

2000

psig0

500

1000

1500

2000

System PressureLess Than pprecharge

System Pressureat pmax

System Pressureat pmin

Accumulator


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Actuator

Hydraulic systems are used to control & transmit power. A pumpdriven by prime mover (electric motor) creates flow of fluid

An actuator is used toconvertthe energy of the fluid back into

mechanical power

Amount of output power developed depends upon the flow rate,pressure drop across the actuator & its overall efficiency

There are TWO types of actuator

1. Linear actuators (hydraulic cylinder)2. Rotary actuators (Hydraulic motors)

Linear Actuators


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Linear Actuators

Linear Actuators


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Linear Actuators

Cylinder actuators provide a fixed length of straight-line motion.

The piston is attached to a rod that extends from one end of the cylinder to

provide the mechanical output. The double-acting cylinder has a port at each end of the cylinder to admit or

return hydraulic fluid.

A four-way directional valve functions to connect one cylinder port to the

hydraulic supply and the other to the return, depending on the desired direction

of the power stroke.

Properties of Linear Actuators


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The cylinders have to be good quality steel with close

tolerances.

There have to be good sealing both at the piston rod and

at the cylinder.

With time dirt may come in and damage the surfaces. This

has to be possibly reduced.

In this case, the leakage will increase all the time.

Properties of Linear Actuators


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Rotary Motor Actuators


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Rotary Motor Actuators

Gear Motors Piston Motors

Vane Motors Limited Rotation Actuator

G M t


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Gear Motor1. External Gear Motor

2 rotating gears, thearea of the gear teeth is

where the pressure acts

to create force

Both gears turn

Simultaneously One gear is connected

to the output shaft and

the other is an idler.

2. Internal Gear Motors

Direct drive gerotor,works much like a

rotary engine.

Two gears, an inner

and an outer.

The pressure pushesthem around a center

point, turning a shaft

V M t


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Vane Motor Spring loaded vanes are connected to a rotor

The rotor turns inside a cam ring (elliptical hole) The vanes slide in and out of the slots in the rotor to make contact

with the cam wall.

Piston Motor


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Piston Motor Many different types of piston motors

1. In-line Piston Motor

2. Radial Piston Motor3. Bent Axis Piston Motor

All of them use the same basic principles

Much like a cylinder, only turns a shaft like the cylinders in your car engine.

Generally the most efficient

High power, high speed, high pressure

1 In-line Piston Motor


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1. In-line Piston Motor

Simple construction

Low cost

Used in low torque high speed applications, such as machine tools

2 Radial Piston Motor


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2. Radial Piston Motor

High Torque

Low speed

Possible application could be a roller.

3. Bent Axis Piston Motor


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3. Bent Axis Piston Motor

Is one example of variable displacement motor.

The angle is altered to change the displacement.

Limited Roatation Actuator


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Limited Roatation Actuator

Also sometimes called a oscillator.

Has limited movement

High torque


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HYDRAULIC

CIRCUIT


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ASSIGNMENT

Draw and Explain the advantages anddisadvantages of hydraulic systems basiccircuit:-

Opened cynosure system Closed cynosure system

Submission Date:

05 Oktober 2013 (Friday) before 5.00pm


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Pure Hydraulic

Design of hydraulic circuit to control the operation ofcylinder follow the sequence

A+ B+ B- A-.

1. Cylinder Rod A moves out

2. Cylinder Rod B moves out

3. Cylinder Rod B moves in

4. Cylinder Rod A moves in

h d l


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B A

3

2

41

Pure hydraulic circuit


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PRESSURE AND FLOW CONTROL ON-

ACTUATORS ACTUATORS HYDRAULIC

SYSTEM


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PRESSURE AND FLOW CONTROL ON-ACTUATORS

ACTUATORS HYDRAULIC SYSTEM

Cylinder rod speed control depending on therequirements of a job.

Circuit that controls the speed of the rod depends onthe position of the flow control valve in a hydrauliccircuit.

There are 3 ways to control speed of rod when it isout: -

Metering Out Metering In

Metering Off


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Metering Out

The control valve is

mounted on the circuit atthe output of hydraulic oilfrom the actuators.

When the pressure ofcylinder achieve the

maximum pressure, oil willflows into the tank.

As the load decreases orsmall, back-pressure is

greater than the pumpoutput pressure.

Metering Out


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Metering In

Flow control valve

mounted on the circuit atthe input ofhydraulic oilto the actuator.

When the cylinderpressure to achievemaximum pressure,hydraulic oil will flow into

the tank.

Metering In


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Bleed Off

Adjustable flow control valve

on this circuit is installed atthe inlet of the hydraulic oilbetween the direct controlvalve and cylinder.

Speed can be controlled by

adjusting the flow controlvalve.

If all the oil drain back intothe tank, cylinder rod will

not move due to the systempressure drop.

Metering Off

2._HYDRAULICS.pdf

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