Valves classified by function and applications

Thread Content

This post was last edited by *aowai99 on 2017-9-6 08:19. The flange manufacturers will introduce to you the classification of valves based on their function as well as their applications. 1. Control valve: When the pressure difference before and after the valve remains constant, for ordinary valves, the flow rate changes little as the opening degree varies over a wide range; however, at a certain opening degree, the flow rate changes sharply, indicating poor control performance. A control valve is a type of valve that can adjust the flow rate by changing the stroke of its valve element, in response to the direction and magnitude of the signal, thereby altering the resistance of the valve. Control valves are divided into manual control valves and automatic control valves, and both types further consist of many different varieties, each with varying control performance. Automatic control valves include self-acting flow control valves and self-acting differential pressure control valves, etc. 2. Vacuum types: Vacuum types include vacuum ball valves, vacuum flap valves, vacuum charging valves, pneumatic vacuum valves, etc. In a vacuum system, components that are used to change the direction of airflow, regulate the flow rate of gas, and shut off or connect pipelines are known as vacuum valves. 3. Special-purpose types: Special-purpose types include pigging valves, vent valves, drain valves, exhaust valves, filters, etc. The exhaust valve is an essential auxiliary component in pipeline systems, widely used in boilers, air conditioning systems, oil and gas industries, as well as water supply and drainage pipelines. It is often installed at high points or bends, etc., to remove excess gas from the pipes, improve the efficiency of pipe utilization, and reduce energy consumption. 4. Shut-off valves: These types of valves are used for opening and closing. It is commonly installed at the inlets and outlets of cold and hot sources, at the inlets and outlets of equipment, and on pipeline branches (including risers); it can also be used as a drain valve and a vent valve. Common shut-off valves include gate valves, globe valves, ball valves, and butterfly valves. Gate valves can be classified into straight-through and concealed stem types, as well as single-plate and double-plate types, and wedge-shaped plates and parallel plates. The gate valve does not seal properly, and large-diameter gate valves are difficult to open ； Along the direction of water flow, the valve body is small in size, resulting in low flow resistance, and the nominal diameter range of gate valves is wide. Based on the flow direction of the medium, stop valves are divided into straight-through, right-angle, and straight-type types, and they can also be classified as those with visible stems or hidden stems. The shut-off tightness of globe valves is better than that of gate valves; they have a longer valve body, resulting in higher flow resistance, with a maximum nominal diameter of DN200. The valve element of a ball valve is an open-ended sphere. When the valve stem is moved to align the opening in the ball with the pipeline axis, it is in the fully open position; rotating it 90° puts it in the fully closed position. Ball valves have a certain degree of regulation capability and can be closed tightly. The disc of a butterfly valve is a circular plate that can rotate around a vertical axis perpendicular to the pipeline axis. When the plane of the valve plate is aligned with the tube axis, it is fully open ； When the plane of the gate plate is perpendicular to the tube axis, it is fully closed. Butterfly valves have a short valve body and low flow resistance, but they are more expensive than gate valves and globe valves. 5. Check valve: These valves are used to prevent the backflow of fluid; they open on their own due to the kinetic energy of the fluid, and close automatically when flow occurs in the reverse direction. It is usually installed at the outlet of water pumps, the outlet of steam traps, and other locations where reverse flow of fluid is not allowed. Check valves are divided into swing type, lift type, and wafer type. In the case of a swing check valve, fluid can flow only from left to right; it automatically closes when flowing in the reverse direction. In the case of a lift-type check valve, when the fluid flows from left to right, the valve core rises to create a passage; when flowing in the opposite direction, the valve core is pressed against the valve seat, thereby closing the valve. For wafer-type check valves, when the fluid flows from left to right, the valve disc opens to create a passage; when flowing in the opposite direction, the valve disc is pressed against the seat, thereby closing the valve. Wafer-type check valves can be installed in multiple positions, and they are compact in size, light in weight, and have a simple structure.