Space produce pneumatic actuators and pneumatic automation
Bettis Rack and Pinion Pneumatic Actuators offer reliable torque to automate valves for a wide range of industrial applications from big to small, hot to cold, general to severe. A stainless steel, high cycle and frequency, extreme temperature, corrosion resistant pneumatic actuator. Stainless steel spring return and double acting pneumatic quarter-turn actuators Output torques to Nm. Designed with a unique helical spline design, which transforms the linear movement of a piston into a quarter-turn rotation, generating high break torques to actuate large valves. Double acting and spring return pneumatic quarter turn actuators for on-off and modulating control of valves in heavy duty service.
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- Pneumatic design 101: Go with the flow
- Pneumatic actuators and systems taking advantage of next generation data
- VIP - Pneumatic Coaxial Valve
- What to Choose for Valve Actuation: Pneumatic vs. Electric Actuators
- Eight selection criteria for actuation components
- How to Decide Between Pneumatic and Electric Actuators
- Types of Electric Linear Actuators
- Aluminium double acting pneumatic actuator DA type
- Pneumatic Actuators for On/off Valves
Pneumatic design 101: Go with the flow
Back to Learn about steam. Control valves need actuators to operate. This tutorial briefly discusses the differences between electric and pneumatic actuators, the relationship between direct acting and reverse acting terminology, and how this affects a valve's controlling influence. One form of controlling device, the control valve, has now been covered.
The actuator is the next logical area of interest. The operation of a control valve involves positioning its movable part the plug, ball or vane relative to the stationary seat of the valve.
The purpose of the valve actuator is to accurately locate the valve plug in a position dictated by the control signal. There are several ways of providing this actuation. Other significant actuators include the hydraulic and the direct acting types. Pneumatic actuators are commonly used to actuate control valves and are available in two main forms; piston actuators Figure 6.
Piston actuators are generally used where the stroke of a diaphragm actuator would be too short or the thrust is too small. The compressed air is applied to a solid piston contained within a solid cylinder. Diaphragm actuators have compressed air applied to a flexible membrane called the diaphragm. Figure 6. The operating force is derived from compressed air pressure, which is applied to a flexible diaphragm.
The actuator is designed so that the force resulting from the air pressure, multiplied by the area of the diaphragm, overcomes the force exerted in the opposite direction by the spring s. The diaphragm Figure 6. The actuator is designed so that with a specific change of air pressure, the spindle will move sufficiently to move the valve through its complete stroke from fully-closed to fully-open. As the air pressure decreases, the spring s moves the spindle in the opposite direction.
The range of air pressure is equal to the stated actuator spring rating, for example 0. To create more force, a larger diaphragm area or higher spring range is needed.
This is why controls manufacturers offer a range of pneumatic actuators to match a range of valves — comprising increasing diaphragm areas, and a choice of spring ranges to create different forces. The diagrams in Figure 6. The direct acting actuator is designed with the spring below the diaphragm, having air supplied to the space above the diaphragm.
The result, with increasing air pressure, is spindle movement in the opposite direction to the reverse acting actuator. The effect of this movement on the valve opening depends on the design and type of valve used, and is illustrated in Figure 6. There is however, an alternative, which is shown in Figure 6. The choice between direct acting and reverse acting pneumatic controls depends on what position the valve should revert to in the event of failure of the compressed air supply.
Should the valve close or be wide-open? This choice depends upon the nature of the application and safety requirements. It makes sense for steam valves to close on air failure, and cooling valves to open on air failure.
The air fed into the diaphragm chamber is the control signal from the pneumatic controller. The most widely used signal air pressure is 0. Consider a reverse acting actuator spring-to-extend with standard 0.
This is shown graphically in Figure 6. Now consider this assembly installed in a pipeline in a pressure reducing application, with 10 bar g on the upstream side and controlling the downstream pressure to 4 bar g. This pressure is acting on the underside of the valve plug, providing a force tending to open the valve.
This force is in addition to the force provided by the air pressure in the actuator. Therefore, if the actuator is supplied with air at 0.
Also, this additional force means that the valve is not closed at 0. In order to close the valve in this example, the control signal must be reduced to approximately 0. The steam pressure in the heat exchanger increases as the heat load increases. This can be seen in Module 6. If the pressure upstream of the control valve remains constant, then, as the steam pressure rises in the heat exchanger, the differential pressure across the valve must decrease.
In this case, the force on the valve plug created by the differential pressure works against the air pressure. The effect is that if the actuator is supplied with air at 0.
In this case, the control signal has to be increased to approximately 1. It may be possible to recalibrate the valve and actuator to take the forces created by differential pressure into account, or perhaps using different springs, air pressure and actuator combinations. This approach can provide an economic solution on small valves, with low differential pressures and where precise control is not required.
More information is given on positioners later in this Module. Note: For simplicity, the above examples assume a positioner is not used, and hysteresis is zero. The formulae used to determine the thrust available to hold a valve on its seat for various valve and actuator combinations are shown in Figure 6.
For many applications, the 0. A higher control pressure and stronger springs could be used, but the practical solution is to use a positioner. This is an additional item see Figure 6. A valve positioner relates the input signal and the valve position, and will provide any output pressure to the actuator to satisfy this relationship, according to the requirements of the valve, and within the limitations of the maximum supply pressure.
The air pressure will also be adjusted as required to overcome friction, therby reducing hysteresis effects. With the second option, the 0. In these circumstances the positioner acts as an amplifier to the control signal, and modulates the supply air pressure, to move the actuator to a position appropriate to the control signal pressure.
For example, if the control signal was 0. It should be noted that a positioner is a proportional device, and in the same way that a proportional controller will always give an offset, so does a positioner. The positioner sensitivity can usually be adjusted. It is essential that the installation and maintenance instructions be read prior to the commissioning stage.
To ensure that the full valve differential pressure can be accepted, it is important to adjust the positioner zero setting so that no air pressure opposes the spring force when the valve is seating. One advantage of a pneumatic control is that it is intrinsically safe, i. To alleviate this, additional components are available to enable the advantages of a pneumatic valve and actuator to be used with an electronic control system.
The basic unit is the I to P converter. This unit takes in an electrical control signal, typically 4 - 20 mA, and converts it to a pneumatic control signal, typically 0. With this arrangement, an I to P electrical to pneumatic conversion can be carried out outside any hazardous area, or away from any excessive ambient temperatures, which may occur near the valve and pipeline.
Most sensors still have analogue outputs for example 4 - 20 mA or 0 - 10 V , which can be converted to digital form. A digital sensor can be directly connected into a communications system, such as Fieldbus, and the digitised data transmitted to the controller over a long distance. Compared to an analogue signal, digital systems are much less susceptible to electrical interference. Analogue control systems are limited to local transmission over relatively short distances due to the resistive properties of the cabling.
Most electrical actuators still require an analogue control signal input for example 4 - 20 mA or 0 - 10 V , which further inhibits the completion of a digital communications network between sensors, actuators, and controllers. Digital positioners. Sometimes referred to as a SMART positioner, the digital positioner monitors valve position, and converts this information into a digital form. Actuators are available to drive rotary action valves, such as ball and butterfly valves. The commonest is the piston type, which comprises a central shaft, two pistons and a central chamber all contained within a casing.
The pistons and shaft have a rack and pinion drive system. In the simplest types, air is fed into the central chamber Figure 6. The rack and pinion arrangement turns the shaft and, because the latter is coupled to the valve stem, the valve opens or closes.
When the air pressure is relieved, movement of the shaft in the opposite direction occurs due to the force of the return springs Figure 6.
It is also possible to obtain double acting versions, which have no return springs. Air can be fed into either side of the pistons to cause movement in either direction.
An adequate compressed air supply system is essential to provide clean and dry air at the right quantity and pressure. Air quality is particularly important for pneumatic instrumentation such as controllers, I to P convertors and positioners.
Where a pneumatic supply is not available or desirable it is possible to use an electric actuator to control the valve. Electric actuators use an electric motor with voltage requirements in the following range: Vac, Vac, 24 Vac and 24 Vdc. The switches are rated at the actuator voltage and may be replaced by suitable relays. Limiting devices are fitted within the VMD actuators to protect the motors from over-travel damage.
These devices are based on either the maximum motor torque or physical position limit switches. Both devices stop the motor driving by interrupting the motor power supply. The controller positions the valve by driving the valve open or closed for a certain time, to ensure that it reaches the desired position. Valve position feedback may be used with some controllers.
In order to position the control valve in response to the system requirements a modulating actuator can be used.
Pneumatic actuators and systems taking advantage of next generation data
Pneumatic systems used in industry are commonly powered by compressed air or compressed inert gases. A centrally located and electrically powered compressor powers cylinders , air motors , and other pneumatic devices. A pneumatic system controlled through manual or automatic solenoid valves is selected when it provides a lower cost, more flexible, or safer alternative to electric motors and actuators. Pneumatics also has applications in dentistry , construction , mining , and other areas.
A valve actuator is the mechanism for opening and closing a valve. Manually operated valves require someone in attendance to adjust them using a direct or geared mechanism attached to the valve stem. Power-operated actuators, using gas pressure, hydraulic pressure or electricity, allow a valve to be adjusted remotely, or allow rapid operation of large valves. Power-operated valve actuators may be the final elements of an automatic control loop which automatically regulates some flow, level or other process.
VIP - Pneumatic Coaxial Valve
This volume set contains chapters, each of size words, with perspectives, applications and extensive illustrations. It is the only publication of its kind carrying state-of-the-art knowledge in the fields of Control Systems, Robotics, and Automation and is aimed, by virtue of the several applications, at the following five major target audiences: University and College Students, Educators, Professional Practitioners, Research Personnel and Policy Analysts, Managers, and Decision Makers and NGOs. Heinz D. He received the Dipl. In he was awarded the title of Docent, and in he was appointed as Professor of Control Engineering in the Department of Energy Systems at the University of Stuttgart. He has authored and co-authored over journal articles, conference papers and seven books. He has delivered many invited lectures and special courses at universities and companies around the world. His main research interests are in the fields of system identification, adaptive control, robust control, control of multivariable systems, neuro-fuzzy control, predictive control, and control of mechatronic systems. He is a member of several national and international professional organisations and a Fellow of the IEEE.
What to Choose for Valve Actuation: Pneumatic vs. Electric Actuators
Hydraulic and pneumatic devices are all around us. They're used in manufacturing, transportation, earthmoving equipment and common vehicles we see every day. The brakes on your car are hydraulically operated; the garbage truck that passes weekly by your house uses hydraulic power to compact trash. Your mechanic uses a hydraulic lift when working on the underside of your car. Pneumatic systems are equally widespread.
Publisher BCT, Inc. Tom Arimes. The title is misleading until you check out the contents.
Eight selection criteria for actuation components
Energized and self-lubricated strips Less friction between piston and cylinder It prevents the bonding of the seal to the cylinder even after long periods of inactivity 2. Slots, bushes and pins made by steel with hardness higher than 50 HRC Higher resistance to the forces inside the actuator 3. Rolling friction between piston and slot Less friction 4.
Finding the right valve or valve actuator for a specific situation can be challenging. Our valve offerings include a broad range of ball valves and butterfly valves. To facilitate remote operation of our valves, we also offer a full product line of pneumatic and electric actuators. BI-TORQ is eager to assist our customers in identifying the appropriate valve actuator solution for their needs. The following page will provide basic background information on pneumatic and electric actuators. A pneumatic actuator facilitates linear or rotary valve motion in automated processes.
How to Decide Between Pneumatic and Electric Actuators
Internal diameter equal to the diameter of the pipe High flow capacity 2. Piston with chemical nickel plating Lower wear of the seals due to the increase of the surface hardness HV 4. Unidirectional flow. Improved fluid dynamics allow minimum pressure losses. See Flow Pressure Diagram. VIP valves can be used in any mounting position horizontal, vertical or oblique. Unsuitable for steam. Unsuitable for mineral products oils, grease, etc..
Types of Electric Linear Actuators
In manufacturing facilities, compressed air is so widely used that it is often regarded as the fourth utility after electricity, natural gas and water. The main reasons are lower upfront and maintenance costs, which combine to make pneumatics the most popular and cost-effective choice for executing mechanical motion. Linear power transmission is typically done with fluid pneumatic with air or hydraulic with oil or electric power.
Aluminium double acting pneumatic actuator DA type
A linear actuator is an actuator that creates motion in a straight line, in contrast to the circular motion of a conventional electric motor. Linear actuators are used in machine tools and industrial machinery, in computer peripherals such as disk drives and printers, in valves and dampers , and in many other places where linear motion is required. Hydraulic or pneumatic cylinders inherently produce linear motion. Many other mechanisms are used to generate linear motion from a rotating motor.
The debate surrounding the pros and cons of electric and pneumatic actuators has been raging for years and still no easy answer exists. Here, with the help of Bimba Manufacturing, we focus on the core differentiators to help narrow your decision. If there is any significant performance differentiator, it is that electric actuators are better known for their high levels of precision. Though this is not to say pneumatic actuators cannot deliver very precise motion.
Actuators can automate valves so that no human interaction with the valve package is necessary to cycle the valve. They can be remotely operated and act as shutdown mechanisms in an emergency situation that would be dangerous for human intervention. At a basic level, an actuator is a control mechanism that is operated by an energy source. This energy—hydraulic pressure, pneumatic pressure, or electric current—moves the internal mechanical parts of the actuator. They are also distinguished by whether they are for quarter-turn e. Double-acting actuators have air or liquid supplied to both sides of the piston with one side at higher pressure, which achieves the movement required to actuate the valve.
Pneumatic Actuators for On/off Valves
When deciding between fluid-driven and electromechanical linear actuators, close consideration of long-term benefits to the intended end user can help original equipment manufacturer OEM system designers maximize both product value and return on investment ROI. Fluid-driven actuators translate electric energy motion through a column of air, gas, oil or other media. While the motion they provide is simpler than with other type actuators, the infrastructure required to support them is not.