Regulator type and selection

Abstract: A regulating valve, also known as a control valve, changes the fluid flow by means of power operation by receiving a control signal output from a regulating control unit. Regulators generally consist of actuators and valves. According to the power used by the actuators it is equipped with, the regulating valve can be divided into three types: pneumatic regulating valve, electric regulating valve, and hydraulic moving regulating valve, that is, a pneumatic regulating valve using compressed air as a power source, and an electric power source as the electric source. Regulating valve, electro-hydraulic regulating valve powered by liquid medium (such as oil, etc.) pressure, in addition, according to its function and characteristics, as well as hydraulic control valve, solenoid valve, electronic, intelligent, fieldbus type control valve Wait.

Valve body type selection <br><br><br> Valve body types are many, commonly used valve body types are straight single seat, straight through two seats, angle, diaphragm, small flow, three links, eccentric rotation, butterfly, sleeve Type, spherical and so on. When making specific choices, consider the following:
(1) The valve core shape structure is mainly based on selected flow characteristics and unbalanced forces.
(2) Wear resistance When the fluid medium is a suspension containing a high concentration of abrasive particles, the internal material of the valve is hard.
(3) Corrosion resistance Due to the corrosive nature of the medium, try to choose a simple structure valve.
(4) Temperature and pressure of the medium When the temperature and pressure of the medium are high and the change is large, the valve whose valve core and valve seat materials are affected by the temperature and pressure change should be selected.
(5) Preventing flashing and cavitation Flashing and cavitation are only produced in liquid media. In the actual production process, flashing and cavitation will form vibration and noise, shortening the service life of the valve. Therefore, in selecting the valve, the valve should be prevented from flashing and cavitation.

Regulator actuator selection <br> In order to make the regulator work, the actuator must be able to generate enough output force to ensure a high degree of sealing and valve opening.
For double-acting pneumatic, hydraulic, and electric actuators, there is generally no return spring. The size of the force is independent of its direction of operation. Therefore, the key to selecting the actuator is to find out the maximum output force and the rotational torque of the motor. For single-acting pneumatic actuators, the output force is related to the opening of the valve, and the force appearing on the regulator valve will also affect the motion characteristics, so it is required to establish a force balance in the opening range of the entire regulating valve.

Actuator type determination
After the output force of the executing agency is determined, according to the requirements of the process environment, select the appropriate actuator. When there is an explosion-proof requirement at the site, pneumatic actuators should be used. Considering energy conservation, electric actuators should be selected as far as possible. If the adjustment accuracy is high, select the hydraulic actuator. Such as the power plant transparent machine speed adjustment, refinery catalytic device reactor temperature regulation control.

The mode of action of the regulating valve
The mode of action of the regulating valve is only available when the pneumatic actuator is selected. The mode of action is formed by combining the positive and negative action of the actuator and the positive and negative action of the valve. There are four types of combinations: positive (air-type), positive-negative (open-type), positive-type (air-open type), and reverse-reverse (air-closed type). Open and air off two. The choice of the mode of action of the regulating valve is mainly considered from three aspects: a) process production safety; b) characteristics of the medium; c) guaranteeing product quality and minimizing economic losses.