FLUID POWER CONTROLFLUID POWER CONTROLUnit – 1

SYLLABUSSYLLABUS1) HYDRAULIC SYSTEMS

Introduction to fluid power system - Hydraulic fluids - functions, types, properties, selection and application.

Construction, operation, characteristics and graphical symbols of hydraulic components – pumps,

actuators/motors, valves, switches, filters, seals, fittings and other accessories.

2) PNEUMATIC SYSTEMS

Introduction, comparison with hydraulic systems and electrical systems. Construction, operation, characteristics

and symbols of pneumatic components. Air treatment – principles and components. Sensors – types,

characteristics and applications. Introduction to fluidics and MRFL.

3) HYDRAULIC / PNEUMATIC CIRCUITS

Reciprocating circuits, pressure dependant circuits, speed control circuits, pilot operated circuits, simple

sequencing circuits, synchronizing circuits, circuits using accumulator, time delay circuits, logic circuits,

cascading circuits, feedback control circuits.

4) DESIGN OF FLUID POWER SYSTEMS

Speed, force and time calculations, Calculation of pressure and pressure drop across components, size of

actuators, pumps, reservoirs and accumulators. Calculations of Heat generation in fluids.

5) APPLICATION, MAINTENANCE AND TROUBLE SHOOTING

Development of hydraulic / pneumatic circuits applied to machine tools, presses, material handling systems,

automotive systems, packaging industries, manufacturing automation. Maintenance in fluid power systems –

preventive and breakdown. Maintenance procedures. Trouble shooting of fluid power systems – fault finding

process, equipments / tools used, causes and remedies. Safety aspects involved.

Unit 1. Unit 1. HYDRAULIC SYSTEMSHYDRAULIC SYSTEMS

Introduction to fluid power system.

Hydraulic fluids

- functions,

- types,

- properties,

- selection and

- application.

Construction, operation, characteristics and graphical symbols of hydraulic components

- pumps,

- actuators/motors,

- valves, switches,

- filters,

- seals,

- fittings and

- other accessories.

INTRODUCTION TO FLUID POWER SYSTEM.INTRODUCTION TO FLUID POWER SYSTEM.

FLUID POWER:

Fluid power technology is a means to convert, transmit, control and apply fluid energy to perform useful work.

Since a fluid can be either a liquid or a gas, fluid power in general includes hydraulics and pneumatics.

Hydraulics employs pressurized liquid and pneumatics employs compressed air.

BASIC LAW:

The basic principle of fluid was developed by Pascal.

He stated that the pressure generated at one point in a confined liquid acts equally in all directions.

The pressure created by piston 1 = Force / Area

= 1 MN / 1 m2

= 1 MN/m2

According to pascal’s law, the pressure acts equally in all directions of the liquid.

So the pressure acting on piston 2 is also 1 MN/ m2.

The force available in the piston 2 = Pressure X Area.

= 1 MN/m2 X 100 m2

= 100 MN.

The advantage of multiplication of force is utilised in fluid power control systems.

APPLICATIONS OF FLUID POWER:APPLICATIONS OF FLUID POWER:

ADVANTAGES OF FLUID POWER SYSTEMS:ADVANTAGES OF FLUID POWER SYSTEMS:

1) Higher torque can be achieved than the electrical systems.

2) Fluid power drives are more compact than the mechanical drives.

3) Multiplication of small forces to achieve greater forces for performing

work.

4) It provides infinite and step less variable speed control which is

difficult to obtain from other drives.

5) Accuracy in controlling small and large forces with instant reversal is

possible with hydraulic systems.

6) Constant force is possible.

7) As the medium of power transmission is a fluid, it is not subjected to

any breakage of parts as in a mechanical transmission.

8) The parts of hydraulic system are lubricated with the hydraulic liquid

itself.

HYDRAULIC FLUIDSHYDRAULIC FLUIDS

Fluids : Liquid / Gases.

The spacing of molecules in gases is much larger than that of liquids and for this reason gases flow more readily than liquids.

The compressibility is measured by Bulk Modulus.

The higher the bulk modulus, the less compressible the fluid or vice versa.

FUNCTIONS OF HYDRAULIC FLUID:

a. Transfer fluid power efficiently.

b. Lubricate the moving parts.

c. Absorb, carry and transfer the heat generated within the system.

d. Be compatible with hydraulic components.

e. Remain stable against a wide range of possible physical and chemical changes, both during storage and while in use.

VARIOUS HYDRAULIC FLUIDS:

1) Water The least expensive hydraulic fluid is water. Water is treated with chemicals before being used in a fluid power

system. This removes undesirable contaminants. Advantages : Inexpensive, Readily available, Fire resistant. Disadvantages : No lubricity, Corrosive, Temperature limitations.

2) Petroleum oils These are most common among the hydraulic fluids which are used

in a wide range of hydraulic applications. Naphthenic oils have low viscosity index so it is unsuitable where the

oil temperatures vary too widely. The aromatics have a higher presence of benzene, and they are

more compatible with moderate temperature variation. Paraffinic oils have a high viscosity index and they are more suitable

for systems where the temperature varies greatly. Advantages : Excellent lubricity, Reasonable cost, Non – corrosive. Disadvantages : Not good for high bearing loads, Poor corrosion

resistance.

3) Water Glycols These are solutions of water and glycol. They contain 35 to 55 percent of water. Advantages : Good fire resistance, Inexpensive, Compatible with

most pipe compounds and seals. Disadvantages : Not good for high bearing loads, Poor corrosion

resistance.

4) Water Oil Emulsion These contain 40% water. The rest is oil, emulsifiers and other additives. The water is dispersed in microscopic droplets surrounded by a film of

oil. Advantages : Good fire resistance, Inexpensive, Compatible with most

seals. Disadvantages : Sometimes difficult to maintain.

5) Phosphate Esters These are organic alcohols attached to a phosphorous atom. They have high thermal stability. They serve as an excellent detergent and prevent build – up of sludge. Advantages : Excellent fire resistance, Good lubricity, Non -

corrosive. Disadvantages : Not compatible with many plastics and elastomers,

Fairly expensive.

6) Silicones These are dimethyl polysiloxanes. They have excellent thermal stability. Advantages : Non – corrosive, Non toxic, Less volatile.

PROPERTIES OF FLUIDS:

PUMPS: Pump converts mechanical energy into hydraulic energy. The mechanical energy is delivered to the pump via a prime mover

such as an electric motor. The principle is that, due to mechanical action, the pump creates a

partial vaccum at its inlet. This permits atmospheric pressure to force the fluid through the inlet line and into the pump.

There are two broad classification of pumps.

1. Hydrodynamic (or) Non positive displacement pumps.

2. Hydrostatic (or) Positive displacement pumps.

HYDRODYNAMIC OR NON POSITIVE DISPLACEMENT PUMPS:

Example: Centrifugal pumps, Propeller pumps.

These pumps provide smooth continuous flow, their flow output is reduced when the circuit resistance is increased.

It is possible to completely block off the outlet to stop all flow even while the pump is running at design speed.

When the resistance of the external system starts to increase, some of the fluid slips back into the clearance spaces causing a reduction in the discharge flow rate.

This slippage is due to the fact that the fluid follows the least resistance path.

Thus the pump flow rate depends not only on the rotational speed but also on the resistance of the external system.

So this type of pumps are used for low pressure, high volume flow application.

HYDROSTATIC OR POSITIVE DISPLACEMENT PUMPS: This ejects a fixed quantity of fluid per revolution of the pump shaft.

The pump outlet flow is constant and is not dependent on system pressure.

So they are well suited for fluid power systems.

Positive displacement pump must be protected against overpressure.

The reason is that a positive displacement pump continues to eject fluid (even though it has no place to go) causing an extremely rapid build up of pressure.

CLASSIFICATION OF POSITIVE DISPLACEMENT PUMPS:

1. Gear Pumpsa) External gear pumps.b) Internal gear pumps.c) Lobe pumps.d) Gerotor pumps.e) Screw pumps.

2. Vane pumps.a) Unbalance vane pumps.b) Balanced vane pumps.

3. Piston pumps.a) Axial design. (1.Bent axis type, 2.Swash plate type)b) Radial design.

GEAR PUMPS

1) EXTERNAL GEAR PUMPS:

INTERNAL GEAR PUMPS:INTERNAL GEAR PUMPS:

LOBE PUMPS:LOBE PUMPS:

GEROTOR PUMP:GEROTOR PUMP:

SCREW PUMPS:SCREW PUMPS:

VANE PUMPSVANE PUMPS

1) UNBALANCED VANE PUMP.

Pressure compensated variable delivery pump:

2) BALANCED VANE PUMP:2) BALANCED VANE PUMP:

PISTON PUMPS:PISTON PUMPS:

AXIAL PISTON PUMP

1) BENT AXIS TYPE PISTON PUMP:

RADIAL PISTON PUMP:RADIAL PISTON PUMP:

HYDRAULIC ACTUATORS:

1) Rotary (continuus rotation) motor – Hydraulic motor.

2) Rotary (limited angle of movement) motion – semi – rotary actuator.

3) Linear motion – Hydraulic cylinder.

HYDRAULIC MOTORS:

Hydraulic motors are classified as follows:

i. Gear type hydraulic motors

ii. Vane type hydraulic motors

iii. Piston type hydraulic motors

a) Radial type

b) Axial type

HYDRAULIC CYLINDER

1) SINGLE ACTING CYLINDER

2) DOUBLE ACTING CYLINDER

(3) CYLINDER CUSHIONING:

(4) TELESCOPING CYLINDER:

HYDRAULIC VALVE(1)PRESSURE CONTROL VALVE:(a)PRESSURE RELIEF (SPRING LOADED TYPE) VALVE:

HIGH-LOW CIRCUIT USING UNLOADING VALVE