Pneumatic Systems

Alex Zenanko

TEC 366

Mr. Chris Marker

FLUID POWER: PNEUMATICS• I. What is Pneumatic?

“A power transmission system that uses the force of flowing gases to transmit power” [ ToolingU.com]

• Word origin is Greek- “Pneuma” meaning “wind, breath”

• II. How big is the fluid power industry?• U.S. $14 billion• $40 billion worldwide

• Trivia: • The first subway was pneumatically powered• Chicago Postal service had miles of underground pneumatic tubes for mail

delivery

EVOLUTIONHISTORIC MODERN

▫ Ancient Greece ▫ Simple devices

Bellows used by blacksmiths

▫ Otto Von Guericke Revolutionized Air

Compressors More Power and Efficient

▫ 1829 first compound air compressor patented

▫ Characteristics of gases explored

▫ Pneumatic hammer and tubes hit the market

▫ Higher Pressure Used▫ Jet Engines▫ Electronic Control▫ Digital Logic Integration▫ Axial Flow Compressors▫ Highly complex

Robotics▫ Standardization

Gases 101• Basic gas characteristics:

• A gas will take the shape of its container no matter the size• Gases are highly compressible• Gases exert a force on the walls of its’ container (can be

measured/predicted)

• Gases have 3 interrelated properties• 1. )Temperature 2.) Pressure 3.) Volume

• Boyles Law- describes the pressure and volume relationship of gases• As volume decreases, pressure increases. (P1 x V1) = (P2 x V2)

• Combinational Gas Law = (Pictured Top Right)

• mathematical representation of the three interrelated properties. “If three conditions of a gas are known, then a change in any one of

the conditions can be predicted if changed”

P=pressure V=volume T=Temperature Kelvin R=Energy Constant

Instant Physics: Gases

TermsPressure- Perpendicular

force per unit area.** Force per unit area acts

on surface area and not mass

Absolute Pressure = [+/-] gauge pressure + atmospheric pressureThis method uses

atmospheric pressure as a reference level to scale from

Pascal’s Law- A pressurized gas exerts an even force on the walls of container. F = P x A

°F to °C: °C = (°F –32) / 1.8 °C °C to °F: °F = (°C x 1.8) + 32

1 H.P. = 4 cfm at 100 psi

Basic Pneumatic System

• A) Compressor– Pressurizes Air– Typically attached to tank for storage – Often is a centralized supply for multiple devices

• B) Check Valve– One way valve– Prevents backflow into compressor– Prevents compression loss when off

• C) Accumulator– Smooth air flow and unwanted disturbances

• D) Directional Valve– Direct Air flow– Stores energy and reduce turbulence – Electrical or manual operation

• E) Actuator– Transfers air energy into motion– Ex. Air Chisel

I. Compressors1) Are commonly powered by electric motors2) Must be matched for each application

– 1. Positive Displacement– Compression Stroke creates pressure– Most diverse field.

– 2.Dynamic– Air velocity creates pressure

-Imagine the energy and power of a river flowing down a mountain. This energy is transferred into pressure.

Positive Displacement CompressorsI. Positive Displacement

• Divisions: Rotary & Reciprocating• Lubrication--- “Wet or Dry”

1. Reciprocating- • 1-50 H.P. applications

• Piston/Cylinder/Valves• Works Like Internal Combustion Engine • 1.)Single, Double Acting and Multistage types

available and describe how air is pumped Double Acting is most common in industry; 100

psi classification

Positive Displacement CompressorsI. Rotary

1) Rotary Screw-• Excellent for continuous operation• 100+ hp applications• Two helical screws placed side by side compress air

when one screw is turned

2) Rotary Vane-• Blades of different length mounted to center hub on

drive shaft• Length difference causes pressure pockets to be

created when drive shaft turns

3) Scroll-• Two offset spiral disc placed on top of each other inside of

circular housing• The top disc remains fixed as the lower disc orbits around the

housing walls• This creates a seal and a vacuum that sucks air in chambers

of varying size• As the bottom disc orbits the chamber size is decreased and

air becomes compressed

Dynamic Compressors

Centrifugal Axial

▫ Uses spinning impeller mounted to solid shaft increase air velocity .

▫ Air is then channeled into a diffuser▫ Diffuser = gradually increases in

size as gas leaves impeller

▫ Spinning Airfoils compress air▫ Airfoils are arranged in fixed

and moving rows along the compression chamber

▫ Extremely Efficient; 90% is achievable

Rotary Screw Compressor Reciprocating Single Acting

Advanced Components• Lubricator

• Automatically lubricates system through air supply. • Oil helps elastomeric seals and moving parts

work• Not all devices require lubrication: A coalescing

filter removes oil

• Muffler aka “Silencer”• Cancels out undesirable frequencies created by

venting exhaust air through porous substance• Coalescing mufflers = reduce sound and oil

• Air Booster Tank and Regulator• Increases air pressure to certain parts of system

• Typically provide a small quantity of high pressure

• Work in-line with system after compressor• Uses: Certain high demand machines; Peak

times that exceed available pressure; 600 PSI• To avoid cost of high performance compresor• Ratio of inlet to outlet pressure change

• Ex.1/2 = Pressure is doubled [is listed in data sheet]

Advanced Components• Aftercooler

• Dissipates heat created by compressing air• Thermal expansion can limit the storage capabilities of a

tank• Pneumatic Logic Components

• Controls the flow of air through the system via controller, actuators and valves

• Very similar to PLC systems• Is becoming more prevalent with advances in computing

and increased machine complexity• Coalescing Filters

• Absorbs oil added to air supply• Is necessary for a system whose components will be

damaged by oil• It is required by OSHA to use a coalescing filter before

exhausting air that has been oiled• Piping

• Friction losses in piping can result in pressure loss• Compressor must be separated from piping with

flexible couplings • to block system vibration

• Ring Lines are those which run in a large loop and feed machines along the loop

• Branch lines are the shorter lines that feed machines and other devices

Piping in Pneumatics1. Installation

1. Must use flexible coupling to between compressor and piping. (Vibration)

2. Piping must sl0pe downward away from compressor at 1-2 degrees [0.12-0.25 in/ft]

3. Use Excess Flow Valve every 100ft

2. Pressure Drop1. Inevitably effects all

pneumatic systems2. Friction and piping length3. A 10% drop in pressure is the

absolute maximum

– Branch lines are the shorter lines that feed machines and other devices

– Ring Lines are those which run in a large loop and feed machines along the loop

Pneumatic Dryer Removes moisture from air. Typically found after Coalescing Filter

and/or FRL1. Dew point suppression = A temperature based scale that

compares change in dew point value before entering the dryer and after leaving the dryer

Question: Air enters a deliquescent dryer at 100 ° F and the dew point suppression is -1.5° F. What is the resulting dew point of the air?

***Moisture within the air will not condense if air temp. stays above 75° F

2. Deliquescent Dryers = Absorption; [ 25° F] D.P.S▫ Air is channeled through salt bed that traps both liquid and vapor

• Must be drained regularly. Typically element is in brick or tablet form

3. Desiccant Dryers = Adsorption ; [ -40° F] D.P.S▫ Moisture is absorbed on surface area of water absorbing substance. Typically silica

gel or activated alumina is used. ▫ “Regenerative Dryer” = a process removes moisture so dryer can be used again

4. Refrigeration Dryer = [ -40° F] D.P.S▫ Industry favorite for a wide range of application due to cheap operating cost▫ Removes moisture by cooling air to the point of condensation. Reheats afterwards ▫ Reduces need for heat sink on compressor up to 60%

Pneumatic Cylinders1) Type of Actuator that does work in the form of

linear motion▫ Can be thought of as the pneumatic muscle

2) Types:1) Single Acting, Double Acting, and Double End Rod

3) Single Acting- ▫ Single Pressure Port▫ Can only be controlled in one direction▫ A spring or load weight must reverse the cylinder’s

movement

4) Double Acting▫ Two Pressure Ports▫ Extension and Retraction can be controlled

5) Double End Rod1) Two rods and Two Pressure Ports; Force is equal for each

rod

6) Area = πr2 1) Find the Area of a ¾” x 1 ¼” cylinder

2) Area = 3.14 x (3/8”)2 Area = 3.14 x .14 Area = .44 in 2

3) Force = Pressure x Area What is the force @ 10 psi

CylindersSingle Acting Spring Return Double Acting

Pneumatic Logic Circuits

1) Logic circuits are made from various valves• Functional equivalent to logic gates• Used to control sequence of events• NOT, OR, AND,

• AND--All inputs must be active• OR--If any input is active the output will be• NOT--The output is the opposite of the input

• NOR and NAND • are combinations of the basic gates

AND OR NOT

-And Valve-Output activated only if A and B are high

-Or Valve-Output activated if A or B is activated

-NOT Valve-Output is opposite of input

Valves• Sequence Valve

• Control sequence of operation between two branches of a circuit.

• A set pressure point will divert flow when reached

• Shuttle Valve• Isolates two supply systems from each other. This valve

supplies an output from one of two inputs that are kept isolated from each other

• Excess Flow Valve• Safety Device. Cuts off flow if pipe breaks

• Pressure Control Valve• Reduce and maintains lower pressure supply to output device. • Is resistive to pressure changes on the supply side

• Limit Valve Field device used to generate and send control logic signal to

processor. -It is active when event has occurred

• Ball Stop Valve• Quick Acting valve; manual turn operation

• Gate Valve• An adjustable wedge impedes the flow of air• Must be rated if used to control pressure

Control Valve Symbology▫ Goal: Determine function of control valve

• 1) Ports/Way 1) Vertical Arrow = Flow Path 2) 45 deg Arrow = Exhaust Path Tee = Closed Path Numbering:

▫ 1 is always pressure port▫ All odd’s > 1 are exhaust ports▫ Even #’s are outlet ports (A & B are also used)

• 2)Position Envelope Indicate discrete # of flow paths.

A Box surrounds a P.E. Depicts each setting and change

^Position 1^ Closed

^Position 2^ Open

2 Position 5 way: 5/2

5 port/2 way valve

Figure 1 Figure 2

Left = Figure 1 : Right = Figure 2

Pneumatics Symbols

1.)FRL [Filter/Regulator/Lubricator] 2.) Single Acting Cylinder 3.) Double Acting Cylinder

-------------------------------------------------------------------------------------------------------

1.)FRL [Filter/Regulator/Lubricator] 2.) Single Acting Cylinder 3.) Double Acting Cylinder

Formulas1. Pressure Dropsid =[Receiver Pressurepsig – Tool Pressurepsig / Line Distanceft

PSID = (RP – TP) / D

2. Compression Ratio = (Pressurepsig + 14.7) / 14.7

CR = (PSIG + 14.7) / 14.7

3. Air Leakage Cost$/min = Flowcfm x Timemin x Electricity UsedkWh/cu-ft x Electricity Cost$/kWh

Leakage Cost$ = cu-ft x min x (kWh/cu-ft) x ($/kWh)

4. Absolute Pressurepsia = Gauge Pressurepsig + 14.7

5. Forcelbs = Pressurepsig x Areasq-in

P = F x A

Pneumatic vs. Hydraulics

Pneumatics Hydraulics

1) Use gases2) Gases are easily

compressed3) Good power density4) Lower Pressures5) Quicker

1) Use liquids2) Liquids compress only

slightly3) Better power density4) Higher Pressures5) Slower

Pneumatic vs. Hydraulics:

Pneumatics Hydraulics

1. Air is abundant and free

2. Less environmental concerns

3. Lower initial cost

4. Higher operating cost

5. Design Simplicity

6. Lower maintenance

1) Must purchase fluids

2) Leaks can harm environment

3) Higher initial cost

4) Lower operation cost

5) Complex Design

6) Very high maintenance

Lab 1 Overview: Flow Measurement• Measuring fluid flow in pneumatic systems is far more

difficult than in hydraulics systems Direct measurement in pneumatic systems can be very

inconvenient however it is more accurate Indirect methods are convenient but sacrifice accuracy

▫ Ex. rotameters, orifice meteres, pitot tubes.

• In this lab we will be using a rotameter• Measurement:

Industrial standard is cubic feet per minute ‘cfm’ for large flow and cubic feet per hour ‘cfh’ for small flow

Corrections must be made using mfg. supplied table

– In this lab we will be using:– Dwyer RMA series Rate-master

Rotameter(100psi)– Vega model 200 Pneumatic System– 5/32” Pneumatic tubing (12” length)

– When connecting tubing to the flowmeter – Eliminate or minimize sharp bends and

flow restrictions when possible– Testing Procedure:

1. Mount the flowmeter vertically2. Connect red hose from compressor

manifold to bottom inlet of the flowmeter 3. Make sure manifold needle valves are

shut4. Turn on compressor 5. Adjust regulator to 20 psi6. Open needle valve slowly two full turns7. Record measurement when ball is

stabalized8. Repeat for 30 and 40 psi9. Find actual airflow using correction

chart

– asdf

Lab 2 & 3. Air Leaks and Cylinders

• Air Leaks cost money. Air leaks are going to happen eventually .

• How to evaluate the cost of leaks is the goal of this lab.

1.) Use the CFM measurements from Lab 12.) Use$.58 cents/ kWh as Al industrial rate avg3.) Assume the motor consumes $.02 kWh/cu-ft4.) Assume the system runs 24 hours a day5.) Apply the air leakage cost formulaLeakage Cost$ = cu-ft x min x (kWh/cu-ft) x ($/kWh)

a

Lab 4. Conveyor• The goal of this lab is to determine the air line configuration for the

conveyor

Positive Displacement

– 1. Positive Displacement• There are (2) main anatomical

divisions• + (1) Variable of Lubrication

• “ Wet or Dry”• Lubricated or Non

Lubricated--”Wet or Dry”• Determined by the type of

compressor and intended use

• Ex. A common aircraft pneumatic system uses graphite vanes inside the compressor that self lubricate

• This system would be classified as “Dry” because it does not use oil for lubrication

– Reciprocating• Piston/Cylinder/

Valves• Works Like Internal

Combustion Engine • 1.)Single, Double

Acting and Multistage types available and describe how air is pumped• Double Acting is

most common in industry; 100 psi classification

– Rotary• Circular Rotation

creates pressure; Can be achieved in numerous ways

• 1.)Rotary Screw-uses two helical screws and used mostly for continuous applications • Pictured top left

• 2.)Rotary Vane-Blades of varying length placed on drive shaft are spun inside housing creating pressure

– Scroll• Two offset spiral disc

placed on top of each other inside of circular housing

• The top disc remains fixed as the lower disc orbits around the housing walls

• This creates a seal and a vacuum that sucks air in chambers of varying size

• As the bottom disc orbits the chamber size is decreased and air becomes compressed

Lab 3. Conveyor• The goal of this lab is to determine the air line configuration for the

conveyor