GORE MAITRAYEE
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Nov 18, 2022
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The most typical device used to control fluid flow in a process is a control valve.
The control valve is a power-operated device that regulates the flow rate of a fluid in a process control system, according to the International Society of Automation.
If a control valve has the right accessories, it will function more smoothly and effectively and be more valuable for process control.
The following list shows the most commonly used accessories with the control valve, as per the requirements.
The vital part of a process control system, pneumatic control valve accessories help to ensure optimal operation.
A converter module is used in a current to pressure device to convert a 4 to 20 mA current input to a proportionate output of 3 to 15 psi pressure.
When a positioner’s high level of positioning accuracy is not necessary for some applications. Only an electro-pneumatic (I/P) transducer can be used in these situations.
When the actuator volume is very large, the control valve positioning reaction speed slows down.
Volume boosters are used to increase a valve assembly’s capacity for pneumatic thrust output. One volume booster is often used by single-acting actuators. At least two volume boosters are necessary for double-acting actuators.
A position transmitter’s main function is to give the control system independent, separate feedback on the position of each valve. As the control valve is used for process monitoring, troubleshooting, or startup/shutdown verification from the control room by an operator, position feedback of the control valve frequently becomes necessary.
The position transmitter, which measures the position of the valve stem or shaft, is directly mounted to the valve yoke.
To lock the valve in its current position in some situations, the solenoid valve will trap air in the actuator. To enable the valve to shift to its no air position in some situations, the solenoid valve will vent out the air from the actuator.
When the valve reaches a particular location within its range of motion, a limit switch is used to deliver a discrete open or discrete close input signal to the control system.
Limit switches located on the control valve and on the yoke can also be used by an operator in the control room for process monitoring, troubleshooting, or startup/shutdown verification.
Only specific feedback on valve position will be provided by these switches. According to our needs, these can be put on the control valve to provide extra feedback signals to the DCS or PLC systems.
In control applications where a specified actuator response is necessary in the event that the air supply pressure is interrupted, trip systems like air lock relays are used. These are utilized with single or double acting actuators to give pneumatic lock-up or with double acting actuators that do not have an inherent air failure condition.
The trip valve causes the actuator to fail up, lock the control valve in the last position, or fail down when the instrument air supply pressure drops below the trip point.
An air volume tank provides the reserve air capacity needed to operate the valve for double-acting applications in the event of an air supply breakdown and while the supply pressure is being restored. The trip valve automatically resets, turns normal, and permits the system to resume normal operation once the air supply pressure has increased above the trip point.
Adjustable travel stops are frequently utilized on the control valve’s handwheels for diaphragm actuators. In an emergency, they also offer a manual method of placing the control valve.
They are arranged in two ways to a control valve.
Travel in any direction can be restricted using the side-mounted handwheel, but not simultaneously in both directions. The control valve’s handwheel can be left in the neutral position to enable automatic operation for the duration of the whole valve movement.
For “infrequent service,” top-mounted handwheels are utilized to manually turn the valve.
There are five basic reasons that accessories are added to a control valve:
In the dynamic world of fluid control, a control valve is one of the most important parts of the processing, usually, they will combine with a couple of accessories to improve the controlling performance, including a handwheel, valve positioner, limit switches, solenoid valves, pneumatic lock-up valves, supply pressure regulators, volume boosters, and quick exhaust valves. In this article, we will explain them one by one, and the assembly method or control solution used in control valves.
control valve accessoriesThe field of engineering relies heavily on control valves as a crucial component in various operations. However, the addition of auxiliary accessories can greatly enhance their functionality and fine-tune processes for maximum efficiency. In this article, we will explore the 8 essential control valve accessories that can revolutionize your operations.
The handwheel stands as a physical testament to the manual control we wield over our systems. It lets us adjust the valve’s position to fine-tune flow control. With every turn, the handwheel brings us closer to achieving the perfect balance in our systems. Whether it’s a minor adjustment of flow capacity or a complete redirection, the power is in your hands.
When it comes to control valves, handwheels form a pivotal aspect, allowing manual operation and fine-tuning of the valve position. Diverse control valve applications necessitate different types of handwheels, each designed with specific advantages in mind. Here, we dive into four key types of handwheels for control valves: top-mounted handwheels, side-mounted handwheels, gear-operated handwheels, and bevel handwheels.
Top-mounted handwheels, as the name suggests, are affixed at the top of the control valve. This positioning provides a clear view of the valve’s operations and allows direct, unobstructed access for easy manipulation. Ideal for valves located at easily accessible heights, top-mounted handwheels are a classic choice for many systems.
Side-mounted handwheels offer an ergonomic alternative for valves located at lower or intermediate heights. By being attached to the side of the valve, they provide easy access and comfortable operation, reducing the physical strain on the operator.
Gear-operated handwheels utilize a gear mechanism to simplify the operation of heavier valves and machinery. The gearing reduces the force needed to turn the valve, making it more user-friendly and efficient, especially for larger control valves that might be challenging to operate manually.
Bevel handwheels incorporate a bevel gear system, offering high torque and precision control. The bevel gear’s angled teeth allow for smooth and efficient operation, ensuring precise valve positioning. This type of handwheel is an excellent choice for applications requiring detailed and accurate control.
Valve positioners play a crucial role in managing the opening and closing of a valve based on a control signal. They come in different types, each with unique attributes designed to optimize performance across a wide array of applications. Let’s dive into the world of valve positioner types.
Pneumatic positioners are the most traditional type of valve positioners. They use air pressure to control the valve’s operation, adjusting the valve’s position based on an input signal. These positioners are known for their simplicity and reliability.
Electro-pneumatic positioners receive an electrical input signal and convert it into a pneumatic output. This conversion makes them a versatile option for various industrial applications where both electrical and pneumatic systems are in use.
Digital or intelligent positioners are the latest advancement in valve positioner technology. They use digital protocols to communicate and interface with control systems. These positioners offer higher precision, better diagnostics, and easier integration with modern control systems.
I/P positioners, or current to pressure converters, convert an up electrical power signal into a proportional pneumatic output. They are typically used in applications where a direct electrical control signal needs to be converted to a pneumatic signal to control a valve.
If the control valve is not assembled with a valve positioner, then the valve does not have proportional control characteristics, only for on/off performance.
control valve with solenoid valve1 Solenoid valve
2 Supply pressure regulator
3 Control valve
The on/off control valve can be realized with the mounting brackets of the solenoid valve as a single mounting device on the valve assembly. This connection does not require additional external pilot power, as the pilot power is fed internally to the solenoid valve.
Control valve with a positioner, a solenoid valve provides additional emergency shutoff to extend the control function of the valve assembly. In this case, the solenoid valve is connected directly upstream of the actuator.
In an emergency, the solenoid valve ensures that the actuator is vented and moved to a fail-safe position. In throttling applications, an external pilot power supply for the solenoid valve is always required
control valve with solenoid valve and positioner1 Solenoid valve
2 Supply pressure regulator
3 Control valve
4 Positioner
In the world of control valves, limit switches are vital accessories that contribute significantly to system safety and efficiency. Their role in monitoring and reporting the valve’s position is pivotal to ensuring that operations remain within designated parameters. Let’s dive deeper into two main types of limit switches used in control valves: indicating type limit switches and mechanical type limit switches.
Indicating type limit switches not only perform the function of traditional limit switches but also provide visual indications of the actual valve position itself. This feature is particularly beneficial in situations where real-time monitoring of valve operations is crucial. They typically utilize a display system, such as LED lights or mechanical flags, to clearly demonstrate whether the valve is open or closed. This immediate, clear visual feedback allows operators to quickly understand the valve’s status and make necessary adjustments, enhancing system efficiency and safety.
Mechanical-type limit switches rely on the physical movement of the valve to activate the switch. As the valve reaches its set limits, it triggers a mechanical arm on the switch, initiating an electrical signal. This traditional type of limit switch is known for its simplicity, reliability, and durability. It serves as an effective tool to prevent the valve from moving beyond its intended range, thereby ensuring operational safety and efficiency.
Whether indicating or mechanical, limit switches play an instrumental role in controlling the movement of valves. By selecting the right type for your specific needs, you can enhance system control accuracy, safety, and efficiency.
Solenoid valves serve as an electrical interface in a predominantly mechanical system. These electrically-triggered valves provide fast and reliable activation or shutdown, ensuring timely response to control signals. They’re the embodiment of modern automation, integrating electrical control with fluid dynamics.
Direct-acting solenoid valves operate through a simple principle: when energized, the solenoid directly opens the valve by lifting the seal off the valve stem and seat. These valves are compact, reliable, and quick to respond, making them ideal for systems that require fast opening and closing.
Unlike their direct-acting counterparts, pilot-operated solenoid valves rely on system pressure to open and close the valve. When the solenoid is energized, it opens a pilot orifice that changes the pressure distribution, causing the valve to open or close. These valves are well-suited for handling larger flow rates and higher pressure systems.
Two-way solenoid valves consist of an inlet and an outlet port, making them ideal for controlling the flow of fluid in a single direction. They operate in an “on/off” manner, either allowing or blocking flow when energized or de-energized.
With an additional port, three-way solenoid valves offer more control options, enabling them to divert flow, mix fluids, or operate double-acting actuators. Depending on the design, these valves can alternate between blocking one port and connecting the other two, or connecting all three ports simultaneously.
Primarily used for operating double-acting cylinders or actuators, four-way solenoid valves have four or more ports. These versatile valves can simultaneously control pressure, exhaust, and flow in two different paths, making them suitable for complex fluid control applications.
Pneumatic lock-up valves function as a fail-safe for pneumatic actuators, severing the signal pressure line under specific circumstances. When the air supply dips beneath a pre-set threshold, or in instances of total air supply failure, the lock-up valves step in to cut off the line. This action freezes the actuator in its current position, hence ensuring it ‘fails in place.’
Standard Method: Pneumatic lockout valves are mounted between the positioner and actuator.
Recommended Version: Type 3709-1 for direct connection to the positioner. This version is particularly compact and uses a minimum of piping.
standard assembly method for lock-up valve for control valve1 Actuator
2 Positioner
3 Pneumatic lock-up valve
Combination with Solenoid Valve: The desired function determines the order in which the device is mounted on the valve assembly.
In the example shown, the pneumatic locking valve is mounted between the actuator and the solenoid valve. In this case, the lockout function takes precedence over the fail-safe action triggered by the solenoid valve.
lock up valve with solenoid valve in control valve1 Actuator
2 Positioner
3 Pneumatic lock-up valve
4 Solenoid valve
Recommended Models – Models 3709-7 and 3709-8 for compact, sandwich-type attachments in combination with rotary actuators. The pneumatic lockout valve is installed between the solenoid valve and the actuator without any piping.
A: The lock-up function takes priority in such a valve assembly. As the last device connected upstream of the actuator, the pneumatic lock-up valve takes precedence. No matter what signal the positioner sends or the position of the solenoid valve, the pneumatic lock-up valve makes the actuator stay put if the supply pressure drops below a certain point.
A: The opening and closing action is sped up by the volume booster, which increases the control signal of the positioner. If we consider the Type 3755 Volume Booster, it feeds the actuator with an airflow output. This output’s pressure is exactly the same as the positioner’s signal pressure, except that it has a much higher volume.
A: The quick-acting shut-off function is carried out by the solenoid valve. In the example, the solenoid valve is activated by the volume booster.
A: The supply pressure regulator ensures a consistent supply pressure to the devices in contact with the hookup.
A pressure regulator accessory for pneumatic control systems and valves works by reducing a high input pressure to a lower, more manageable output pressure. It adjusts to changes in the input pressure or demand for the output pressure, providing a steady and reliable output regardless of these fluctuations. This reliable regulation helps prevent damage that can be caused by pressure spikes to component, such lik pneumatic actuator, and enhances overall system efficiency.
Pneumatic volume boosters have a straightforward setup and ideal boost ratio. They’re easy to adjust using a screw, perfect for different uses. They can work in very cold conditions, as low as -55 °C. The Type 3755-2 model has an extra flange with a threaded exhaust port. This port lets you guide the used air out through a pipe or back in to clean the actuator spring chamber. You can choose this model in either stainless steel or aluminum.
In a typical setup, the volume booster is placed between the positioner and the actuator. To keep the air supply clean and pressure steady, it goes through a supply pressure regulator before reaching the booster. This way, the volume booster provides the actuator with a flow of air that matches the signal pressure from the positioner but in a much larger volume.
standard control solution for volume booster in control valve1 Positioner
2 Supply pressure regulator
4 Control valve (failclose)
6 Pneumatic volume booster
When used with a solenoid valve, the solenoid valve is positioned between the volume booster and the actuator. It’s important to make sure the solenoid valve is big enough to handle all the air the volume booster can put out.
booster valve with solenoid valve in control valve1 Positioner
2 Supply pressure regulator
3 Solenoid valve
5 Control valve (fail-open)
6 Pneumatic volume booster
Quick exhaust valves are all about speed. They allow for rapid release of exhaust air, enabling quick cylinder return. By speeding up the exhaust process, these valves contribute to faster valve responses and overall system efficiency.
Quick exhaust valves work to make pneumatic actuators vent faster. The Type 3711 Quick Exhaust Valve stands out due to its compact size and ability to handle a lot of air. A built-in restriction lets you change how fast the valve responds, matching the needs of your project. If needed, you can guide the used air out through a pipe, and it can even be reused to clean the actuator spring chamber.
Quick exhaust valves are installed between the positioner or solenoid valve and the pneumatic actuator. They are used to speed up the exhaust capability, allowing the whole pneumatic system and actuator to vent faster.
The example shows a standard connection, activated by the positioner, with another solenoid valve connected between the positioner and the quick exhaust valve.
The integrated restrictor allows for optimal adjustment of the response behavior, making the 3711 type quick exhaust valve adaptable to various valve assemblies and their control behaviors. For instance, opening the restrictor allows the quick exhaust valve to participate in closed-loop control after major signal changes occur. This can counteract overshooting, especially in response to minor signal changes. The control valve’s setting is fixed with a cotter pin.
improve control valve response time1 Positioner
2 Pneumatic actuator
3 Solenoid valve
4 Quick exhaust valve
5 Silencer
This design shows a valve assembly for pneumatic control valves with a fast closing and fail-in-place function. As the last device connected upstream of the pneumatic actuator, the pneumatic locking valve has priority. Regardless of the signal from the positioner and the position of the solenoid valve, the pneumatic lock-up valve will hold the actuator in the last position as long as the air supply pressure is below a certain limit.
lock up function with priority for control valves1 Actuator
2 Supply pressure
regulator
3 Positioner
4 Limit switch
5 Solenoid valve
6 Pneumatic volume booster
7 Pneumatic lock-up valve
The volume booster will boost the positioner’s control signal accordingly, thus speeding up opening and closing action. When using the Model 3755 booster, it provides the actuator with exactly the same airflow output pressure as the signal pressure from the positioner, except that it is larger.
The quick respond close function is performed by a solenoid valve. Performed by a solenoid valve, in the example the booster activates the solenoid valve. In the example, the solenoid valve is activated by the booster. The air supply pressure regulator provides a constant air supply pressure to the connection unit.
The following design shows a control valve assembly with adjustable capacity, closing time, and quick opening function. By using two boosters, the opening time of the control valve and especially the opening time of the control valve can be accelerated. The closing time can be adjusted within a certain range. The closing time can be adjusted within a certain range.
A solenoid valve activates two connected intensifiers for the quick opening function. When the solenoid valve is energized, the control valve is in a closed-loop control state: The positioner provides a control signal for the two boosters and boosts accordingly. The air supply pressure regulator provides constant air supply pressure. supply pressure.
adjusting the control valve close time1 Actuator
2 Supply pressure regulator
3 Positioner
4 Limit switch
5 Solenoid valve
6 Pneumatic volume booster
7 Restriction
The hook-up for emergency venting consists of a pneumatic actuator, a positioner, a limit switch, and a solenoid valve.
When the valve’s movement goes beyond or falls below a set limit, a sensor on the limit switch sends out a signal. This signal can activate the solenoid valve, leading to the emergency venting of the actuator.
emergency venting system operates for control valve1 Solenoid valve
2 Supply pressure regulator
3 Control valve
4 Positioner
5 Limit switch
If your control system needs for a unique design, you’re in the right hands with THINKTANK. As a professional control valve manufacturer based in China for over 32 years, we have the expertise and experience to offer an optimal solution for your project. Trust in our technical excellence and let us deliver the quality and reliability your operations need.
For the mentioned model for this article we use Samson’s accessories, if you want to learn the details, please feel free to click here.