Fluid Power School
Fluid Power School BY Mikecole1911 Original – November 10, 1994 “BASIC PNEUMATICS & FLUID POWER” l. Basic definition of Fluid Power: A fluid is any media that will flow when contained in some form of vessel or conductor such pipe, hose or tubing. The media can be air, oil, water, gases etc. The media when moved with pressure or force is capable of producing ready energy, which can be used to perform limitless automated functions. Fluid power is most often used to create linear and or rotary motion. The forms of fluid power discussed in this forum are pneumatic technology with some light coverage of hydraulics.
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A. Trends with Fluid Power: 1. The field of hydraulics is a growth industry in the USA. The primary cause for this expansion is the fact that many manufacturers in the US are automating a great deal of heavy manufacturing industries in order to compete with overseas developing nations, and the European and Japanese manufacturers that have already been in the automation mode for many years. Hydraulic technology is the heavy-duty muscles of manufacturing, no other form of industrial power provides as much work capability at a competitive cost.
Along with this muscle come environmental oncerns, proper disposal of warn out hydraulic oil, old strainers and filters are issues that need to be addressed. The other obvious area is leaks in hydraulic systems are a constant nuisance. 2. Pneumatic technology is growing rapidly every year. This is largely due to many factors; Pneumatic fluid power is clean, less expensive to implement than hydraulics, and economical to use. As the domestic manufacturing base moves toward lighter high tech type industries, compressed air still provide more “bang for the Buck” than any other power source without the negative environmental effects of hydraulics.
Linear and rotary motion can be generated with great speed, reliability and precision using pneumatic cylinders, air motors and rotary actuators. Compressed air technology has seen great expansion as original equipment manufactures (OEMS) continue to utilize pneumatic systems on their machines and equipment. Most of the time the customer has plant air available for use, but in some cases OEM’s are using small on board compressors that are quiet, efficient and capable of producing ample volumes of compressed air at pressures up to 150 psig. The copier industry and medical fields are two major examples.
Almost anyone can benefit from a working knowledge of basic pneumatic capability. That is the intent of this seminar, to provide a basic exposure of general capabilities that could be employed to meet the pneumatic needs in your business. Seminar Format: A: Generic presentations of various fluid power components: The basic functions and variations of the major components available in the Fluid Power Industry. B: Review the basic layout of a pneumatic system. 2. FRL & Gauges 3. Safety Blow Down Valve (Lockout valve) 4. Directional Control Valves 5. Actuators – Cylinders, rotary actuators, air motors, Robotic Grippers etc. Accessories – Flow Controls, needle valves, pressure switches, check valves, vacuum generators, relief valves etc. 7. Pneumatic Logic (alternative to PLC) C: ANSI Symbol Handout and Overview: D: Basic Pneumatic Schematic Handout: 1. Review Pneumatic ANSI symbols 2. Walk through schematic Ill. Generic Presentations of Components Compressor: There are several types of air compressors on the market today. The most common are rotary screw and reciprocating piston type compressors. Most compressors require oil similar to automobile engines to extend life and keep them running moothly.
This oil is almost always present in the compressed air sent into the plants air system. The oil can be in the form of burned off hydrocarbons, air line or airborne oil in liquid or vapor form. Compressor selection for a facility is not the focus of this seminar, but Component Supply is an authorized Ingersoll Rand Dealer and we can assist anyone that needs to select a compressor for your facility. A full range of portable or on board compressors are also available that range from sizes small enough to fit in the palm of your hand, to 2 horsepower units.
These small ompressors generate surprisingly high volumes of air and vacuum at pressures up to 150 psig and vacuum to 28. 8″ Hg. These compressors are usually “oiless” in design and are an industry unto them selves. Liquid handling systems and process control are other areas that can be assisted by the use of fluid power technology. As stated before, anything that flows can be dealt with using this industrys equipment and technology. So keep this in mind for any needs you may have that fit this general description. FRL & Gauges: FRL’s or filters, regulators and lubricators are used to properly condition the air for use in a pneumatic system.
These combination units can be provided in full size confguration or a more compact miniature version. Many people assume that com pressed air is clean by its nature, this is a great misnomer and poor quality compressed air will cause components to wear faster, and inhibit the reliability of the system. Compressed air is a control medium Just as is electricity; it needs to be conditioned from raw form in order to work as expected. Electricity must be filtered and so does air. The contraction FRL is also the order in which the conditioning proc ess takes place.
Air is first filtered, and then regulated to the proper working ressure and, in some systems it is then lubricated to improve the function of various components. A pressure gauge mounted to the regulator will indicate the operating pressure in the system. Properly conditioned air is the grass roots toa well-designed fluid power system. Filtration: Particulate – Function and dynamics 2. Depth Filtration-Torturous Path 3. Contaminant Removal 4. Water removal -Removes water in droplet form no vapor removal. 5. Element micron size – Element Materials Polypropylene and Sintered Bronze 6.
Flow rating vs. element rating – finer rating yields lower flow. Coalescing – Function and ynamics – 1 . Oil Removal-Droplet and aerosols 2. Particulate removal-Depth filtration 3. Aerosol removal – coalescing style filters filters out oil aerosols and their negative effects to system reliability are removed as well. 4. Life expectancy of the element – average 3-6 months. Check the color Brown = need for change. 5. Material is borosilicate glass Pre-Filter desirability, 5 Micron particulate filters extend life and function of Coalescing unit. 6.
Flow capability / pressure drop Options for Filters: Polycarbonate or Metal Bowls Automatic and Manual drains 2. 3. Sight Glasses 4. Diverter blocks . Mounting Options A. Nipple Mount B. Modular Mount Systems Maintenance – general WATER REMOVAL: Water in pneumatic systems has been a common problem for circuits that use on board oiless compressors. This is because there is usually not much distance between point of use for the air and the compressor the temperature of compressed air is elevated after compression and drops rapidly when it travels through the system.
This temperature drops result in the dew point being reduced all the way through the system and developing water as the higher temperature of newly compressed air-cools and expands. In most industrial plant pneumatic systems a refrigerated air dryer is used to cool the compressed air and remove most of the water before it ever leaves the compressor room. Particulate filters are very efficient water removers when the water is in droplet form. Simple heat exchangers such as coiled copper tubing and serpentine bending arrangements have proven VERY effective at getting the water into droplet form.
This allows the filters to take the water out of the system and thus improve reliability. Todays technology also allows you more tolerance for water in the system than older types of valve and cylinder esigns. We never advocate water as acceptable in the systems but components that can handle it will make your system more reliable and efficient. Pressure Regulators: What is their purpose in the system 1 . Function and Dynamics – Two way normally open valves with diaphragm or piston as the regulation device. 2. Relieving and Non-relieving Styles 3. Regulation ranges – 0-20, Instrument, 0-60 Low, 0-125 General 4.
Mounting options 5. Tamper resistance – Caps, Keys, Removable knobs 6. Maintenance – general Lubricators: 1 . Function and Dynamics – Sump-siphon tube-bypass check valve needle valve sight ome. 2. Flow required allowing the lubricator to function (2 SCFM Minimum) 3. Forms of Lubricators Fog Type: Fog Type lubricators are best applied for general-purpose type applications where the components are not sensitive to over lubrication or very precise lubrication. Micro Fog Type: Micro Fog Type lubricators are best applied in those applications where the components require fine-metered oil mist lubrication.
This type of unit provides a more uniform supply of atomized oil mist. Drop type: Drop Type lubricators are best applied for general-purpose type applications where the omponents are not sensitive to over lubrication or very precise lubrication and the oil mist is not required to be as fine as those created by mist type lubricators. The oil dispensed from drop type lubricators will travel the shortest distance to components. 4. Maintenance – general refilling procedures, fill under pressure, button fill features, bowl removal potential wear and failure points. Integral Filter / Regulators 1.
Form Function and Dynamics 2. Advantages 3. Particulate Filters are usually the only type available in (“Piggy Back”) units. Some are now available in Coalescing style units. 4. Safety Blow Down Valves (Lockout Valve): Safety blow down valves are three way valves that shut off the air supply to a machine or system and then exhaust the remaining air in the machine to atmosphere. The primary purpose of this item is for SAFETY. Valves of this type are an absolute must in any machine, control circuit or system. By exhausting the residual air in the machine to atmosphere there is no stored energy in the machine.
One last cycle in the machine could crush an operator’s hand or cause other types of injury. This is an OSHA requirement that should NEVER be ignored. Remember, a 2. 5″ ore air cylinder with 80 psig pressure behind it has 400 lbs. of force ready willing and able to do great damage if accidentally cycled. Lockout valves function and features: Lockout or blows down valves are three way valves usually with a palm button or lever actuator positioned to allow the operator to depressurize the machine by hitting the button in an emergency. The air supply is terminated and residual pressure in the system is exhausted.
A Lockout Valve: A lockout valve is the same function as described above except a padlock device is also provided to allow a service technician to lock the air supply in the off position. This guarantees safety to the technician when working on the machine; he can physically lock the valve in the closed position. Directional Control Valves: Directional control valves are utilized to control the operation of fluid power actuators or direct the flow of fluids in more than one direction. A single acting actuator requires Pressure in one direction to operate and a spring or load will return it.
A three way directional control valve is used to operate a single acting actuator. A actuator. A four way directional control valve is used to operate a double acting unit. These components will be explained in detail later on. There are many functions of valves in industrial automation systems, 85% of all directional control valves for cylinder, air motor, or rotary actuator control are four way valves. Actuator control is not the only purpose directional control valves serve, the designer is really only limited to their own creativity. Valve Function and Flow Patterns Two Way Valves 1.
Normally Open (Passing) 2. Normally Closed (Non-passing) Three Way Valves 3. Diverter 4. Selector Four Way valves 1. 2-Position 2. 3 Position – spring or detent centered 3. Dual Pressure (Balanced Spool required) Valve Actuators 1 . Solenoid – Direct Acting 2. Solenoid – Air Pilot Assist 3. Manual 4. Mechanical 5. Air Pilot 6. Manual Overrides Valve operation – general descriptions as to what options are available to achieve the specific need of your application. How do different operators work? Example: Double Solenoid vs. Single Solenoid Valve Design and Configuration 1.
Poppet Style A. Armature Style Direct Lift (Direct Acting) B. Rubber Poppet (Pilot Assisted) 2. Spool Valves (Balanced vs. Unbalanced) A. Dynamic Seal B. Lapped Spool and Sleeve C. Bonded Spool D. Lapped Spool in Body A. In Line Mount B. Bar Stock Manifold Mounting C. Flexible Manifold Mounting/ Electrical interface options Sub-D 25 PIN, Fieldbus etc. 4. Stacking Mounts – Custom designs for the OEM or special needs. 5. Accessories A. Sandwich Flow Controls B. Sandwich Regulators C. Blocking Discs D. Blank Station Plates E. Exhaust Restrictors F. Indicator Lights / Surge Suppression G.
Integral vacuum generators attached to valves Cylinders Cylinders provide linear motion that can be used to perform a limitless amount of mechanical functions. Cylinders are available from fractional bore size up to 24″ bore and beyond providing a range of forces capable of achieving almost anything. Air cylinders usually employ some type of elastomer sealing mechanism such as an “O” ring or lip type seals. Hydraulic cylinders sometimes use elastomer seals for lower pressures (1500 psig and below) or automotive style metallic piston rings for higher pressures of 5000 psig and higher.
They can sometimes be thought of as air cylinders on steroids. Because hydraulics was the first form of fluid power air cylinders that followed were at first nothing more than converted hydraulic cylinders with soft seals (leather initially) that would be leak free with air. As a result air cylinders were at first ver designed and a classic case of overkill. In the past decades air cylinders have been streamlined and cost reduced to meet the cost/function goals of todays industrial market. There are basically two forms of cylinders, single acting and double acting.
A single acting cylinder requires pressure from one direction to extend or retract it, and uses a spring or the weight of the load to operate it in the opposite direction. (Usually operated by a three-way valve) The side of the piston opposite the pressure source must be allowed to vent to atmosphere if it’s an air cylinder or return to tank if it’s a hydraulic cylinder. A double acting cylinder requires pressure in both directions to extend and retract the cylinder. (Usually operated by a four-way valve) The side of the piston that is not being pressurized is allowed to exhaust back through the valve either to atmosphere or to tank.
Cylinder Styles and Confgurations A. Roll crimped Stainless Steel – Bimba Style B. Barrel Type Threaded body C. NFPA Tie Rod Design – Interchangeable Type D. Low Profile or Pancake Style E. Power Slides F. Rodless Cylinders/Cable Cylinders/Band Cylinders G. Linear Thrusters/ Non-Rotating Cylinders H. Parts Feed Escapements l. Rolling Diaphragm Style Cylinders K. Multi-Position Cylinders (Duplex Cylinders) L. Position Feedback Cylinders M. ISO Interchange IS06431 & IS06432 Cylinder Features and Function A. Cushions B. Bumpers C. Shock Absorbers D. Position Sensing 1 . Magnetic Reed Switch (MRS) 2.
Hall Effect Switch 3. Integral Mechanical Proximity Switches 4. Integral Mechanical Pneumatic Switches 5. Transducer Probes-position Feedback E. High Temperature F. Pressure Breakaway issues and specifications Special Cylinders in General Speed Control of Cylinders (Speed can be made variable to need) A. Flow Controls B. Needle Valves C. Exhaust Restrictors/Speed Control Mufflers D. Fixed Orifice Meter In vs. Meter Out – speed control methodology Factors That Reduce Cylinder Life A. Side Load B. Poor Quality Air C. Too Much Lubrication D. Improper Mounting – Creates Side Load E. Stroke Length – Long Strokes F.
Bottoming out on The End Caps G. High Cycle Rates High or Low Temperature Calculating Cylinder Force The force that an air cylinder is capable of producing can be calculated by taking the area of piston diameter and then multiplying it by the airline pressure you have available. You must remember to deduct the piston rod area from the retract side of he piston because your working pressure will not be able to act on this surface. A key point to remember is that fluid power is FLEXIBLE power by reducing or increasing your working pressure you can decrease or increase your force exerted at a known rate. The formula for this calculated using: 0 x roo x Line pressure = Output stroke or rotation of a pneumatic device. Electrical drive mechanisms generally do not have this feature and are limited in stroke or travel. Air Motors Air Motors provide rotary motion with a shaft that can be continuous in either one or both directions. The air motor is an alternate source of power in lieu of the electric motor. Air motors can be stalled without damage or a rise in heat, which is a real advantage over electric motors. Air consumption and exhaust noise is the two major concerns for air motors.
It is also important to note that air motors must be lubricated. Vanes are used inside the motor for the air to act on and drive the shaft. There is a known amount of leakage past the vanes when the motor is both stalled and operational. Adjusting the working pressure exposed to the motor can vary the power or torque provided by an air motor. Valve selection and speed control options are basically the same as would be used for air cylinders. A unidirectional air motor is analogous to a single acting air cylinder and a Bi-directional motor is analogous to a double acting cylinder.
Rotary Actuators Rotary actuators provide rotary motion to a shaft through conversion of cylinders attached toa rack and pinion or a vane. As the rack and pinion move or the vane moves the attached shaft provides rotary motion usually not more than one revolution or 3600, when the rack or vane is returned to the home position the shaft is also returned to the home position. The actual rotation of the shaft can be specified when ordering usually this is done in 450 increments. The actuator can be single acting and returned with a spring or double acting and returned with pressure.
Rotation adjustments are very handy and reduce the need for extreme tolerances of other mechanisms that help reduce overall machine cost. Styles and Rack and Pinion Style A. Single Rack vs. Double Rack B. Backlash – How to eliminate it. C. Higher in precision than vane type D. Shaft Vs. Flange output Vane Type A. Low Cost B. High Breakaway C. Shorter Life D. Higher Rate of Leakage E. Limited Range of Rotation (2700 Max) Control of Actuator Motion – A. Valving 4 Way valves 2 & 3 position valves. B. Speed Control of actuators 1 . Flow Controls 2. Needle Valves 3. Fixed Orifice 1.
Bumpers 2. Cushions 3. Hydraulic Shock Absorbers C. Accuracy – the precision of a rotary actuator is usually a function of control and design by the end user. The implementation of hard stops and bumpers etc determine type ability to achieve maximum repeatability. Options For Rotary Actuators Position sensing – all of the switching options that are available on cylinders are also available in rotary actuators as well. Proximity sensing can also be used in both external and even internal formats. A. Rotation Adjustment *** C. Dual shafts D. Multiple Angles E. Cushions – Bumpers F.
Non Standard Port Location G. Specials Pneumatic Robotic Grippers Grippers are usually used in higher-level automation systems where pick and place type functions are required. Depending on the style and confguration needed the grippers can range from being very low cost to several hundred dollars. Remember one very important fact “you can always purchase a better gripper for less money than it costs to design and make your own”. 1. Basic Styles A. Parallel Grippers Jaws move in parallel motion. B. Angular Grippers Jaws move in angular parallel motion 900 Grippers 1800 Grippers 2.
Basic Features and Function A. Stroke Adjustments B. Open and Closed Sensors C. Single and Double Acting D. Optical Encoder Option E. Repeatability from Gripper to Gripper (key for field service) F. Operational repeatability l. Accessories and Miscellaneous Components A. Flow Controls – C. Check Valve D. Pressure Switches E. Vacuum Generators G. Relief Valves H. Quick Exhaust Valve REV. B – Revised 03/07/93 enhanced coverage expanded verbiage of descriptive areas. REV. C – Revised 09/10/93 tailored format and topics to OEM business and imaging machine needs.
REV. D. – Revised 11/10/94 to have a more generic appeal. REV. E. – 1 1/1 5/95 Converted File from WordStar 6. 0 to MS Word 7. 0, removed some information that does not apply to customers. REV. G – 05/21/2001 Updated basic wording in various areas. July 17, 1995 Pneumatic Logic Introduction: Pneumatic Logic is a control medium very similar to electricity. Over the years the popularity of pneumatic control logic has varied depending on several issues such as reliability, cost, troubleshooting, technology and application nvironments.
Moving Parts Logic (MPL) – Also Known as Pilot Logic, MPL can be used in conjunction with or in lieu of electrical controls on automated machines. This form of control medium was very popular in the 1970’s due to lower cost and small size compared to relay electrical control systems. Todays PLC’s have closed that gap in a dramatic fashion. Today MPL has its place in hazardous applications such as paint spray booths or areas where a spark could cause an explosion. In automated assembly or automatic machines Pneumatic Logic is still the lowest cost form of Anti-tie Down echanisms and assembly processes that require 5 or less steps.
After 5 steps or more the PLC is often (but not always) lower in cost and smaller in size than MPL, it also offers better diagnostics for debug. When used in conjunction with Air Pilot operated power valves, manually and mechanically operated Limit Valves MPL allows for sequencing, time delays, parts sensing, position sensing etc. Almost any automated process can be achieved with MPL. Pneumatic Logic when applied properly is also very compact and highly reliable. 1. Mounting Formats A. Individual Bases