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.
Improve Your Plant Efficiency with 8 Essential Control Valve Accessories
The 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.
1. Handwheel
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.
Types of Handwheels
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
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
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
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
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.
2. Valve Positioner
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
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
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
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
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.
Assembly method without Valve positioner
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.
1 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.
Assembly Method with Valve Positioner and Solenoid valve in control 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
3. Limit Switches
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
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
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.
4. Solenoid Valves
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.
Types of Solenoid Valve
Direct-Acting Solenoid Valves
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.
Pilot-Operated Solenoid Valves
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
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.
Three-Way Solenoid Valves
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.
Four-Way Solenoid Valves
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.
5. Pneumatic Lock-up Valves
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.’
Assembly methods for lock-up valve in control valve
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.
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.
1 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.
Q: What is the priority function of a valve assembly with quick-acting shut-off and fail-in-place features?
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.
Q: How does the opening and closing action of the valve assembly get accelerated?
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.
Q: Which part of the valve assembly performs the quick-acting shut-off function and how?
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.
Q: How is a constant supply pressure provided to the devices in the hookup?
A: The supply pressure regulator ensures a consistent supply pressure to the devices in contact with the hookup.
6. Pressure Regulators
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.
7. Volume Boosters
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.
Standard Assemble Solution for Volume Booster in Control Valve
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.
1 Positioner
2 Supply pressure regulator
4 Control valve (failclose)
6 Pneumatic volume booster
Assembly Design of Solenoid Valve Combine with Volume Booster in Control Valve
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.
1 Positioner
2 Supply pressure regulator
3 Solenoid valve
5 Control valve (fail-open)
6 Pneumatic volume booster
8. Quick Exhaust Valves
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.
How to improve the response time for control valves?
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.
1 Positioner
2 Pneumatic actuator
3 Solenoid valve
4 Quick exhaust valve
5 Silencer
Design of Lock-up function with priority for control valves
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.
1 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.
How to Adjustable Control Valve closing time
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.
1 Actuator
2 Supply pressure regulator
3 Positioner
4 Limit switch
5 Solenoid valve
6 Pneumatic volume booster
7 Restriction
What Control Valve Accessories Should Consist of Emergency Venting?
The hook-up for emergency venting consists of a pneumatic actuator, a positioner, a limit switch, and a solenoid valve.
How does the emergency venting system operate for Control 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.
1 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.
