1. Shut-off Valves
These valves are used for opening and closing. They are commonly installed at the inlet and outlet of cold and heat sources, equipment inlet and outlet, and pipeline branches (including risers). They can also be used as drain valves and vent valves. Common shut-off valves include gate valves, globe valves, ball valves, and butterfly valves.
Gate valves can be classified as rising stem or non-rising stem, single gate or double gate, wedge gate or parallel gate, etc. Gate valves have poor sealing tightness, and large-diameter gate valves are difficult to open; the valve body size is small along the water flow direction, resulting in low flow resistance, and the nominal diameter range of gate valves is large.
Globe valves are classified into three types according to the medium flow direction: straight-through, right-angle, and direct-flow, and are further divided into rising stem and non-rising stem types. Globe valves have better sealing tightness than gate valves, but the valve body is longer, resulting in higher flow resistance. The maximum nominal diameter is DN200.
Ball valves have a perforated ball as their valve core. A ball valve is fully open when the valve stem is turned so that the orifice of the ball is aligned with the pipe axis; a 90° rotation closes it completely. Ball valves offer some regulating capability and provide a tighter seal.
A butterfly valve has a circular valve plate as its valve core, which can rotate along a vertical axis perpendicular to the pipe axis. It is fully open when the valve plate plane is aligned with the pipe axis; it is fully closed when the valve plate plane is perpendicular to the pipe axis. Butterfly valves have a shorter valve body and lower flow resistance, but are more expensive than gate valves and globe valves.
2. Check Valves
These valves prevent backflow of the medium. They open automatically using the fluid's own kinetic energy and close automatically when the flow reverses. They are commonly installed at pump outlets, steam trap outlets, and other locations where reverse flow is not permitted. Check valves are classified into three types: swing, lift, and wafer. For swing check valves, the fluid can only flow from left to right; reverse flow closes automatically. For lift check valves, the valve core rises when the fluid flows from left to right, creating a passage; reverse flow closes the valve core against the valve seat. For wafer-type check valves, when fluid flows from left to right, the valve core is opened, forming a passage; when flowing in the opposite direction, the valve core is pressed against the valve seat and closed. Wafer-type check valves can be installed in multiple positions, are small in size, lightweight, and have a compact structure.
3. Control Valves
When the pressure difference across a valve is constant, the flow rate of an ordinary valve changes little over a large range of opening degrees, but changes drastically at a certain opening degree, indicating poor regulating performance. Control valves can change the valve core stroke according to the direction and magnitude of the signal, thereby changing the valve's resistance and achieving the purpose of regulating flow. Control valves are divided into manual control valves and automatic control valves, and both manual and automatic control valves have many types with different regulating performances. Automatic control valves include self-operated flow control valves and self-operated differential pressure control valves, etc.
4. Vacuum
Vacuum valves are components used in vacuum systems to change the direction of airflow, regulate the flow rate, and cut off or connect pipelines.
5. Special Purpose Valves
Special purpose valves include pigging valves, venting valves, drain valves, exhaust valves, and filters.
Exhaust valves are essential auxiliary components in piping systems and are widely used in boilers, air conditioning, oil and gas, and water supply and drainage pipelines. They are often installed at high points or bends to remove excess gas from pipelines, improve pipeline efficiency, and reduce energy consumption.
