A sanitary valve control top is a device that provides real-time information about the performance of a sanitary valve electronically, and is mounted on top of the valve actuator. It can tell operators if a valve is open, closed, or partially open.
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Donjoy Valve Control Unit C-TOPValve control unit (C-TOP) is an electronic device that is used to control and automate industrial valves. It works by receiving instructions from a control device or a computer and then using
A valve control top serves three main functions. First, it provides status of the valve- is the valve open or closed? Second, it provides an "action"- the ability to open or close the valve. Finally, a control top provides feedback- did the valve open or close as intended? In the control top are individual components that help accomplish each of these three functions. Now, let's do a deeper dive on each of those.
Position Switches
For the first function- valve status or position indication- we use a switch. A switch in a valve control top detects a moving probe- usually a linear valve stem- and indicates valve change of state. The switch then sends a signal back to the main PLC to confirm the valve position.
There are a few different kinds of switches we see in Waukesha valve control tops, including microswitches, proximity switches, Hall Effect, and inductive sensors. We won't go too deep on each kind of switch, just know that microswitches are a mechanical technology common in pasteurizer divert applications in Grade A dairies, while promixity switches are probably the most common type of switch detect a moving probe without making physical contact with the target, and inductive switches are used in newer "set and forget" applications. But ultimately, they all do the same thing- provide information about valve position.
Solenoids
The next function we have is "action". Solenoids are what allows valves to actuate or change position. Solenoids are basically little electrical air check valves that control air flow into the valve actuator. Solenoids are typically provided in the "closed" state, meaning no air can flow through. When the valve coil is energized, however, a little plunger lifts, allowing air to flow forward into the valve actuator, causing the valve to open or change position. When the coil is de-energized, air supply to the actuator is stopped and the valve position returns to the closed or alternate position.
In Waukesha and APV control tops, solenoids are available in 110VAC and 24VDC versions. We should also mention that solenoids may not always be located in the valve control top. Occasionally, they can also be located in a remote panel, with poly flow or stainless air tubing routed the valve.
Feedback
The final function our control top carries out is valve feedback or communication. Ultimately, the control top needs to tell the rest of the system what is going on in the valve. There are a number of ways to do this- ranging from a simple wired terminal strip, to an industrial communications card- such as ASi or DeviceNet- which can simplify the wiring, addressing, and communication of 100's of valves. Again, we won't get into the specific pro's and con's are DeviceNet or Profibus here, just know that one of the primary functions of the valve control top is to communicate with the rest of the system.
In sum, while valve control tops are often bright and provide visual indication of valve state, their three primary functions are to provide status of the valve, actuate or control the valve, and provide feedback to the rest of the system on the status of the valve. It accomplishes this with position switches, solenoid valves, and feedback cards.
What is the purpose of a postioner in a control valve?
A positioner for a control valve is used to adjust a valve's position based on a desired set point for a process variable, whether it be pressure, temperature, or flow.
How does a positioner work?
Producers typically install valve positioners on the yolk or top casing of a pneumatic actuator for linear control valves. On rotary control valves, the valve positioner is installed in line with the valve and actuator stems on top of the actuator or on the side of the actuator. Installation depends on what type of actuator one uses.
Affixing the positioner to the actuators allows the positioner to measure the stem travel (linear valves) or degree of rotation (rotary valves). This also changes the position of the valve as required based on the input signal from the instrument controller.
When the process variable differs from the desired set point, the instrument controller sends an electrical or pneumatic signal to the positioner. This varies its pneumatic output to the actuator to move the valve open or closed accordingly. This occurs until the process variable reaches the desired set point.
How many types of positioners are there?
There are 3 primary types of positioners:
Pneumatic Valve Positioner
Electro-Pneumatic (EP) Valve Positioner
Digital Valve Positioner
In any hygienic fluid processing environment, finding ways to increase productivity while reducing the potential for human error can add considerable dividends to the bottom line. Valve automation through the use of control tops is one strategy processors use more and more to accomplish this goal. In this article, we will discuss how automated valves work when connected to a control top and outline the latest technological improvements in these fields.
All valves in a process plant contain what are called valve actuators, which are simply the valve mechanisms that actually open and close the valves. Simple valves that are opened and closed manually typically use a lever or a wheel to operate the valve.
Most process plants with a large number of valves, though, have automated valve actuators for opening and closing valves. This valve automation is operated via air pressure, hydraulically, or electronically. Automated valve actuators are commonly found in process plants in the pharmaceutical manufacturing and in the food & beverage processing industries.
They are typically used to control butterfly valves, seat valves, and mixproof valves in process pipelines that contain a large number of valves.
Most types of automated valve actuators may be fitted with an optional device called a control top. As the name implies, control tops are mounted on the top of the valve actuator and are used to provide real-time information, electronically, about the performance of the valve.
Control tops tell process plant operators whether each valve in their system is open, closed, or partially open. Information that is transmitted via valve actuator control tops may be looped into a system network, controlled via a PLC (programmable logic controller), or monitored remotely from a control room in the process plant.
In process piping installations that contain a large number of automated valves, installing control tops on valve actuators can provide a number of advantages.
They notify the pipeline operator if each and every valve in their system is operating properly, and set to the correct position for the intended operation.
Automation provides significant cost savings. For example, without a control top a PLC may think that a particular valve is open when it actually isn't. As a result, thousands of dollars worth of product could accidentally be sent down a waste drain or contaminate a large storage silo.
Due to the peace of mind afforded by control tops, most large process pipeline system operators will pay for the extra cost to install control tops on their automated valve actuators as a risk mitigation measure.
Control Valves vs. Regulators in Control Applications
Understanding the differences between regulators and control valves is crucial in the automation industry. Each of these holds equal importance but have different functions and also operate in a different way. It is important to be knowledgeable about both solutions so that control process designers do not engage in major problems or waste money and resources.
Understanding the Difference
First, in order to understand the differences between regulators and control valves we should look into the components of each. In terms of design, a typical control loop allows control valves to employ a range of process variables. This depends on which variable is being measured for control (flow, level, temperature, pressure…). The process control variable is first measured by a sensor or transmitter and then sent to a host control system. More times than not, this system is known as the DCS or Distributed Control System. This system is responsible for interpreting how the valve should respond to a deviation from the set point value (predetermined). After this occurs a signal is communicated back to the DCS control which in return reports the degree of which the actuator needs to close or open the valve in order to return back to the predetermined set point.
Operationally, the main difference between a control valve and a regulator is that regulators are better defined as process powered valves without the demand for an external power or even an instrument air source to operate. Typically, a regulator applies the pressure of the controlled process fluid against a diaphragm. The same diaphragm then rejects a compressed spring in order to achieve forced balance with the diaphragm at a given set pressure. If there is any change in the controlled pressure the diaphragm is forced to move. This then causes the flow area of the regulator to change which allows more or less process fluid to flow.
Since the use of process fluid pressure is a means for control, regulators are functional as pressure control valves.
Another difference comes in relation to the design pressure rating of the body of the regulator. Control valves are able to handle the same pressures on the outside of a valve as they are on the inlet side. However, a regulator may have a lower pressure rating on the control pressure side of itself (the regulator). Why? You might ask. This is because the process fluid pressure is being directly applied to the components of the diaphragm casing.
One more difference is speed. Compared to control valves, a regulators speed of response is faster. Regulators are able to respond instantly to changes occurring in the controlled pressure.
As far as maintenance they are also easier to maintain and have no volatile emissions.
Control valves, however, are available in larger sizes and are in higher pressure classes than regulators are.
Choosing the Right Solution for the Right Application
Regulators, usually, are associated with a lower cost for maintenance and installation. But it is also important to keep in mind that many projects spec in the use of an actuator with its valve for their control applications.
In some situations a control actuator and valve package or a regulator should not be used. This is due to the fact that certain applications mean technical advantages for either a control valve or a regulator. Some of these examples include:
Tank Blanketing
This is also known as blanket gas control and is the process of maintaining the pressure of a mass of inert gas at the top of a tank or container which prohibits contact with the outside air. Regulators are often used for the pressure-reducing valve as well as for the back pressure regulator because they are able to monitor the tank pressure directly as well as respond more quickly to any changes. However, it may be necessary to use a valve with a throttling actuator if it is not possible to set a safety relief valve to a pressure below the design pressure of the regulator.
Differential Pressure Control
In oil and gas production, maintaining production pressure coming from the rig is critical. The wellhead pressure is continuously varying. This means that a positive differential pressure from the pipeline must be maintained without the line being over pressured. If the extraction happens in an area where power supply is available, control valves can be used. However, some production sites are located in remote areas and thus do not have access to power supply, eliminating valve actuators as an option. Regulators, on the other hand, are capable of maintaining differential pressure between the reference point and outlet pressure without the use of power supply.
Boiler and Heater Control
This can be understood as an application that commonly uses a control valve and a regulator together. In normal operational standards, a large volume of gas is required to fuel the system. This typically results in using a high-capacity valve used for control.
Extreme Service Conditions
Often times the term known as service is applied to automation applications where things such as excessive vibration, cavitation (formation of vapor cavities in a liquid causing excessive wear), or flashing occur due to excessive pressure drop across the valve. If bubbles or flash evaporation with moderate pressure drops are expected, or any pressure drops, regulators should be avoided. Control valves have trim designs capable to manage wide variations or extreme spikes of pressure as well as reduce potential damages due to cavitation.
Knowledge-based decision
Understanding the differences between regulators and control valves is crucial in the automation industry. Each of these holds equal importance but are different in the way they function and operate. If one understands the capabilities and functions of valve actuators as well as regulators, those whom are tasked to select from the two options will be able to select with confidence.
The valve positioner is a feedback mechanism. It allows valves to be positioned precisely in accordance with the output signal of the controller, in the presence of major disturbances caused by unbalanced forces acting on the valve stem, changes in actuator temperature, etcetera. Even a relatively small actuator, that otherwise would have to be bench-set to an unacceptable degree, can be stroked precisely when a valve positioner is used to signal the valve position.
Positioners are not now considered to be the universal solution to many problems. In fact, in some control circuits the effect of fitting a positioner can be detrimental. Whilst it is an advantage to use positioners in slow systems, it can be a disadvantage in the case of control loops with short reset times. A positioner should also be considered for relatively slow systems, such as mixing/separation, level, and temperature control when the volume and mass of the fluids handled are large compared to the process action. The best solution is to correctly size the valve actuator and spring and ensure that the valve functions correctly without the need for a positioner.
The use of a positioner however should be considered for:
Split-range systems, where a controller controls more than one valve; although it is now preferable to split the controller output electronically and control each valve in a range by a full range signal from the control room.
Valves where the actuator working pressure is greater than the control signal pressure, higher actuator pressures are used to provide sufficient force to ensure correct valve movement, a frequently used range is 0.4 to 2.0 barg, 6 to 29 psig.
Actuators operating at higher pressures to increase actuator "stiffness".
Where it is necessary to achieve the best possible control with a minimum of overshoot and the fastest possible reaction in systems with long pneumatic signal lines between the valve and regulator. In this case it would be better to use electric analogue or digital signal transmission.
Where the control loop reacts slowly to changes in valve position, and accurate positioning is therefore desired.
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For many years, as a leader in the pump and valve industry, Donjoy has been adhering to the tradition of excellent innovation and maintaining excellent quality. The products manufactured by Donjoy comply with a series of international standards and specifications such as ASMEBPE, EHEDG, FDA, 3A, etc., and have passed the EU Pressure Equipment Directive (PED-97 / 23 / EC) and (MD-06) implemented by the German TüV agency. / 42 / EC) certification, 3-A sanitary standard certification implemented by the US 3A agency, EU ATEX explosion-proof certification, China Safety Valve Special Manufacturing Equipment (TS) license and China Quality Certification Center GB / T 19001-2016 / ISO 9001: 2015 quality management system certification and many other international authority certifications.
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