Selection of Pneumatic Control Valve for Working Characteristics

Selection of Pneumatic Control Valve for Working Characteristics

(1) The differential pressure control valve should be matched with the differential pressure of the pipeline outside the valve

The working characteristic curve of the pressure difference control valve varies depending on the pressure difference outside the valve network. Therefore, in the design selection and actual operation of the pipeline network, it should be ensured that the pressure difference of the pipeline network at the installation position of the valve varies within the allowable range of the valve. Excessive or insufficient actual pressure difference will cause the spring to fail, resulting in the valve not functioning properly.

(2) Selection of pressure difference setting for differential pressure control valve

The set pressure difference of the differential pressure control valve should match the resistance of the pipeline system inside the valve at the design flow rate to ensure that the valve operates in its optimal working area. If the difference between the two is too large, it will cause the actual flow rate of the pipeline system inside the valve to be too large, resulting in hydraulic imbalance of the pipeline system outside the valve or causing the actual flow rate of the pipeline system inside the valve to be too small, which will affect the heating effect.

(3) Selection of Diameter for Differential Pressure Control Valve

The flow range controlled by differential pressure control valves of different diameters varies. When selecting valves, the design flow rate of the pipeline system inside the valve should be set within the optimal working area of the valve control flow range, preferably on the larger side, based on the valve's operating characteristic curve. Choosing a valve diameter that is too small to operate at the high-end of its control flow range can easily generate noise. Choosing a valve with a large diameter to operate at the lower end of its control flow range can cause a large range of changes in system flow, leading to hydraulic imbalance in the external pipeline system and economic waste. Generally, it is better for the valve diameter to be equal to or one size smaller than the interface diameter of the pipeline system inside the valve.

(4) Differential pressure control valve cannot replace flow control valve

The purpose of using differential pressure control valves is to enable thermal users to adjust the flow rate within a certain range according to their heating needs. The heating system using differential pressure control valves is a variable flow system. But currently, most heating networks are determined based on the basic needs of heating, and it is difficult for the network system to achieve unlimited heating according to demand, which will inevitably cause hydraulic imbalance in the network system. Especially in heating systems that only install pressure difference control valves without heat meters, hydraulic imbalance is particularly serious. In the transitional stage from meeting basic heating needs to on-demand heating, there are two ways to solve this contradiction: ¢Ù increasing the flow of the pipeline network; ¢Ú Limit the flow at the thermal inlet or on the branch line. The method of limiting flow is to set a flow control valve. The flow control valve can be a self operated flow control valve to automatically balance the flow in the pipeline network. Install self operated flow control valves at each thermal inlet, which is more expensive and therefore less commonly used. Another way is to install a self operated flow control valve on the branch line. At present, the vast majority of thermal inlets use locked flow control valves, which requires manual adjustment work to be done during the initial operation of the pipeline network. This work is time-consuming, laborious, complex, and difficult to adapt to changes in the working conditions of the heating network. But this is an economic measure to ensure the hydraulic balance of the heating pipeline network