Nov.08.2024
1. Selection Issues of Control Valves
Currently, the commonly used control valves in engineering are electromagnetic valves and electric valves. However, both have their drawbacks in usage. Electromagnetic valves are prone to blockage by foreign objects, have high water resistance, and require long-term specialized maintenance. On the other hand, electric valves, while having no water resistance issues, face challenges in terms of necessary control circuits, leading to concerns about the impact of water vapor infiltration on their lifespan.
2. Maximizing Overcoming the Impact of Scaling on Valve Usage
Scaling, whether in electromagnetic or electric valves, not only causes valve leakage but can also seriously affect the normal operation of the valve. Therefore, addressing the impact of scaling has become a widespread concern in the industry.
However, the differences in design, actuation mechanisms, and use of sealing materials contribute to variations in the performance of control valves:
The presence of dead zones in the manufacturing process can cause process variables to deviate from the original setpoint. Therefore, the controller's output must increase enough to overcome the dead zone, and only then will this corrective action take place.
1) Primary factors affecting dead zones: Friction, backlash, valve shaft rotation, and amplifier dead zones. Different control valves are sensitive to friction in various ways. For example, rotary valves are very sensitive to friction caused by high seat loads, so attention should be paid to this during use.
2) Wear: Wear is inevitable during normal valve usage, with the lubrication layer experiencing the most significant wear. Different fillings lead to significant differences in friction.
3) Friction from packing: Friction from packing is a major source of friction in control valves, and different fillings result in significant differences in friction.
4) Type of actuator: Different types of actuators fundamentally impact friction. Generally, spring diaphragm actuators are better than piston actuators.
3. Design Issues of Positioners
From the initial design thinking, the design of actuators and positioners must be considered together. How to design a good positioner? Knowing its important characteristics, it must be a high-gain device, consisting of static and dynamic gains. Increasing static gain is achieved by designing a preamplifier, such as a nozzle-baffle device.
Dynamic gain is obtained through a power amplifier, typically a sliding valve. Nowadays, some people use microprocessors to set positioners. It seems that valves will "speak" to us about their issues in the future, making maintenance simpler. A high-performance positioner with high static and dynamic gains can provide the best overall performance in reducing process deviations for any given valve component.
