fluid pneumatic circuits

7/28/2019 Fluid Pneumatic Circuits

1/7

BASIC PNEUMATIC CIRCUITS

INSTRUCTED BY:

NAME

COURSE

INDEX NO

GROUP

FEILD

DATE OF SUB

Gunasekera N.P.A.

B.Sc. Engineering

090160U

03

Mechanical

05 .04.2012

ME 3022


2/7

INTRODUCTION

Fluid power systems are pressurized moving fluids, either liquid pr gas, within an

enclosed circuit to generate, transmit, and control power. The term fluid power applies to both

hydraulic and pneumatic. Hydraulics uses pressurized fluids, while pneumatics uses compressed

gases. Fluid power can be effectively combined with other technologies through the use of

sensors, transducers and microprocessors. Generally, both hydraulics and pneumatics systems

have many advantages over the other types of power transmission systems including

Multiplication and variation of force, Easy and accurate control, High power/low weight, Low

speed and torque, Constant force or torque, Safety in hazardous environments, etc. hydraulic

power transmission systems, which use pressurized liquid such as oil or water, are widely used in

practical applications where higher forces and/or accurate control are needed. Key sectors of

applications include mobile systems, industry and special areas such as aerospace engineering.

The usefulness of using compressed air such as a power source is as:

1. Cleanness2. Pressure is transmitted undiminished in all direction throughout the system3. Low cost4. The best solution for the jig and fixture systems, automation lines, picks and place

in electronics industry.

However, a typical maximum pressure for the pneumatic systems is 7 to 10 bars. This

indicates that the pneumatic systems arent suitable for the heavy duty in terms of load.

EXPERIMENT: Basic Pneumatic Circuits

OBJECTIVE : To familiarize with pneumatic power transmission systems

PROCEDURE

According to the given diagram in the lab sheet we have to set up a pneumatic circuit

which can operate a double-acting cylinder remotely through the use of an air pilot-actuated

DCV. Using a low pressure (10 psi) for supplying two pushbutton valves and activating them

manually causes the main DCV to activate for cylinder retraction or extension.


3/7

DISCUSSION

1. Components of a basic pneumatic circuita) Compressor: Pump that compresses air, raising air pressure to above ambient pressure

for use in pneumatic systems. There are several types of compressors used

in the industrial.

I. Reciprocating compressorsReciprocating air compressors are positive displacement compressors. This means they

are taking in successive volumes of air which is confined within a closed space and elevating this

air to a higher pressure. The reciprocating air compressor accomplishes this by using a piston

within a cylinder as the compressing and displacing element.

II. Rotary Screw CompressorsRotary air compressors are positive displacement compressors. The most common rotary

air compressor is the single stage helical or spiral lobe oil flooded screw air compressor. These

compressors consist of two rotors within a casing where the rotors compress the air internally.

There are no valves. These units are basically oil cooled (with air cooled or water cooled oil

coolers) where the oil seals the internal clearances.

Since the cooling takes place right inside the compressor, the working parts never

experience extreme operating temperatures. The rotary compressor, therefore, is a continuousduty, air cooled or water cooled compressor package.

III. Centrifugal CompressorsThe centrifugal air compressor is a dynamic compressor which depends on transfer of

energy from a rotating impeller to the air. The rotor accomplishes this by changing the

momentum and pressure of the air. This momentum is converted to useful pressure by slowing

the air down in a stationary diffuser.

IV. Rotary sliding vane compressorA sliding (rotary) vane compressor has a solid rotor mounted inside a water jacketed

cylinder, similar to that of a jacketed water section of a reciprocating cylinder. The water jacket

around the cylinder is used for cooling. The rotor is filled with blades that are free to move in

and out of the longitudinal slots in the rotor. Blade configurations range from 8 to 12 blades,

depending upon manufacturer and pressure differentials. The blades are forced out against the

cylinder wall by centrifugal force, creating individual cells of gas which are compressed as the

rotor turns. As it approaches the discharge port, this area is reduced and the gas discharged.


4/7

b) Pneumatic Cylinder or Linear ActuatorThese devices are used to apply straight line (linear) pushing or pulling forces. Linear

actuators are available in thousands of different configurations. These cylinders are fitted with

pistons of various diameters and strokes of various lengths. They are most commonly specified

as single acting (powered in one direction) or double acting (powered in both directions). Single

acting spring return cylinders are more economical with respect to air consumption.

Double acting cylinder

Double-acting cylinders (DAC) use the force of air to move in both extends and retract strokes.

They have two ports to allow air in, one for outstroke and one for instroke. Stroke length for this

design is not limited; however, the piston rod is more vulnerable to buckling and bending.

Addition calculations should be performed as well.

c) Solenoid ValveSolenoid valves are electrically operated valves that control the direction and flow of

pressurized air to and from pneumatic actuators or circuits. Solenoid valves can be either mono-

stable, (they spring return to a default condition either on or off) or Bi-stable, (having no

preferred or default condition thus remaining where it was last positioned either on or off)

Pneumatic valves can be operated by hand, (mechanical) electrically (solenoid) or air (piloted)

operated.

Ports and Positions of a 3-2 Valve

The first number 3, refers to the number of ports or holes through

which air moves into or out of the valve and the 2 refers to the number

of valve positions or conditions.

3/2 way pushbutton operated valve (normally close) with spring return.

A three-way directional valve has three ports, each of which serves a different purpose.

The first port is used to connect the valve to an actuator or another device. The second port is

connected to an air-flow. The third port is used as an exhaust exit. When the first and second

ports are open and the third is closed, air moves through the valve to the device. When the first

and third ports are open and the second port is closed, the actuator can vent exhaust. Three-way


5/7

valves are often connected to actuators in cylinders, or used in pairs and connected to double-

acting cylinders.

5/2 way double pilot valve

Four-way valves are also available with five external ports, one pressure port,

two actuator ports, and two exhaust ports. Such valves provide the same basic control of flow

paths as the four-ported version, but have individual exhaust ports. In the fluid power field this is

referred to as a "five-ported, four-way valve." This type of valve brings all flow paths to

individual external ports. The pressure port is connected to system pressure after a regulator.

Actuator ports are connected to inlet and outlet ports of a cylinder or motor. Each exhaust port

serves an actuator port.

d) RegulatorRegulators control circuit pressure or force.These devices are fitted with mechanical

components that react to changes in the downstream air pressure. The regulator attempts

to automatically maintain a constant (preset) pressure within a pneumatic circuit as long

as the supply (reservoir) pressure is greater than the required circuit pressure. The reading

on the regulator-mounted gauge indicates the regulated or circuit pressure.

e) Operation of filtersA pneumatic filter is a type of filter specifically designed for use in a compressed air

stream. Filters are devices used to remove contaminants from a stream of liquid or gas.

Pneumatic filters remove contaminants, especially solid particulates, from streams of fluid in theform of compressed air. They are frequently used in sequence with secondary filters that trap

even smaller particles that escape the primary filters.


6/7

2. Advantages of pneumatic systems

Reliable, economical actuators. Pneumatic actuators, the air-powered motors whichcontrol valves and dampers, remain the most reliable, durable, and economical actuators

available. They require essentially no maintenance except for inspection and adjustment

of the echanical linkages. It is easy to select actuators which fail in the desired position

upon loss of electric power (and thus pneumatic air pressure). Pneumatic actuators, of allsizes, cost much less than corresponding electric/electronic actuators.

Flexible, modular control components. The complete pneumatic control system aredistributed throughout the building using numerous pneumatic building blocks such as

thermostats, receiver controllers, and pneumatic relays. Virtually any control strategy can

be implemented by a custom-designed pneumatic control system. Pneumatics can provide

excellent control performance and can maintain set points accurately.

Compressed gas can be stored, allowing the use of machines when electrical power islost.

Safety is assured,o Very low chance of fire (compared to hydraulic oil).o Machines can be designed to be overload safe.

3. Disadvantages of pneumatic systems

Good maintenance is required.Pneumatics require two important types of maintenance.The first is to ensure that the pneumatic air supply is clean, reliable, and dry at all times.

The second is to carry out a program of routine and preventative maintenance under

which all control components are inspected and, if necessary, adjusted every couple of

years or so.

Pneumatic controls are not well-suited for remote monitoring of space conditions andmechanical equipment status.

Cannot be used where accurate positioning or rigid holding is needed (due tocompressibility of air)

Sluggish (slow) response

Poor lubricant Air can be corrosive since it contains Oxygen and water


7/7

4. Practical applications of pneumatic systems

Air brakes on buses and trucks Air brakes, on trains Air compressors Air engines for pneumatically powered vehicles Cable jetting, a way to install cables in ducts Compressed-air engine and compressed-air vehicles Gas-operated reloading Holman Projector, a pneumatic anti-aircraft weapon Inflatable structures Lego pneumatics can be used to build pneumatic models Exercise machines Pipe organs

fluid pneumatic circuits

Documents