Working Principle and Classification of Adjusting Valve

In the automatic control of modern factories, the regulating valve plays a very important role. The production of these factories depends on the correct distribution and control of the flowing medium. Whether it is energy exchange, pressure reduction or simple container feeding, these controls require certain terminal control components to complete.

Ⅰ. Definition of adjusting valve

The regulating valve acts as a variable resistance in the pipeline. It changes the turbulence of the process fluid or provides a pressure drop in the case of laminar flow. The pressure drop is caused by changing the valve resistance or friction. This pressure reduction process is commonly referred to as throttling. For gas, it is close to the isothermal adiabatic state, and the deviation depends on the degree of non-idealness of the gas. In the case of liquid, the pressure is consumed by turbulent flow or viscous friction, both of which convert pressure into heat energy, resulting in a slight increase in temperature.

A common control loop consists of three main parts. The first part is a sensitive element, which is usually a transmitter. It is a device that can be used to measure the adjusted process parameters, such as pressure, liquid level or temperature. The output of the transmitter is sent to the regulating instrument-the regulator, which determines and measures the deviation between the given value or expected value and the actual value of the process parameter, and sends the correction signals to the final control element one by one-regulation valve. The valve changes the flow rate of the fluid, so that the process parameters reach the desired value. The regulating valve belongs to the series of adjusting valves. Its main function is to adjust the pressure, flow, temperature and other parameters of the medium. It is a control element in the process loop.

Ⅱ. Working principle of the adjusting valve

The regulating valve is used to regulate the flow, pressure and liquid level of the medium. The working principle of the regulating valve is to automatically control the opening of the valve according to the signal of the regulating position, so as to achieve the adjustment of the medium flow, pressure and liquid level. Adjusting valves are divided into electric adjusting valves, pneumatic adjusting valves and hydraulic adjusting valves. The regulating valve is composed of two parts: electric actuator or pneumatic actuator and regulating valve. Regulating valves are usually divided into two types, straight-through single-seat regulating valve and straight-through double-seat regulating valve. The latter has the characteristics of large flow capacity, small imbalance and stable operation, so it is usually especially suitable for occasions of large flow, high pressure drop and a little leakage.

Ⅲ. Classification of adjusting valve

1. According to the characteristics of the stroke, the regulating valve can be divided into straight stroke and angular stroke. Straight stroke includes single seat valve, double seat valve, sleeve valve, cage valve, angle valve, three-way valve and diaphragm valve. Angular stroke includes butterfly valve, ball valve, eccentric rotary valve and full-function ultra-light regulating valve.

2. The adjusting valve can be divided into the following categories according to the driving mode, including manual adjusting valve, pneumatic adjusting valve, electric adjusting valve and hydraulic adjusting valve, electric adjusting valve with electricity as power source and hydraulic regulating valve powered by the pressure of a liquid medium such as oil.

3. According to the adjustment form, it can be divided into adjustment type, cut-off type and adjustment cut-off type.

4. According to the flow characteristics, it can be divided into linear, logarithmic (percentage), parabola and quick opening.

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