What Are The Valve Classifications

By function and purpose
（1） Shutoff valves are valves that open and close. It is usually installed at the inlet and outlet of cold and heat sources, the inlet and outlet of equipment and the branch line of pipeline (including stand pipe), and can also be used as the drain valve and air release valve. Common shut-off valves include gate valve, globe valve, ball valve and butterfly valve.
Gate valves can be divided into rising stem and non-rising stem, single gate and double gate, wedge gate and parallel gate, etc. Poor tightness of gate valve and difficult opening of large-diameter gate valve; Small valve body size along the flow direction, small flow resistance and large nominal diameter span of gate valve.
Globe valves can be divided into straight-through type, right-angle type and straight-through type according to the medium flow direction, and can be divided into rising stem and non-rising stem. The closing tightness of the stop valve is better than that of the gate valve, the valve body is longer, the flow resistance is larger, and the maximum nominal diameter is DN200.
The valve core of ball valve is open ball. Move the valve rod so that the opening of the ball is fully open when facing the pipe axis and fully closed when rotating 90 °. The ball valve has a certain regulation performance and can be closed tightly.
The valve core of butterfly valve is round valve plate, which can rotate along the vertical axis vertical to the pipeline axis. When the valve plate plane is consistent with the pipe axis, it is fully open; When the gate plane is vertical to the pipe axis, it is fully closed. The length of butterfly valve body is small, the flow resistance is small, and the price is higher than that of gate valve and globe valve.
（2） The CHECK VALVE is a kind of valve used to prevent the medium from flowing backwards. It opens automatically by the kinetic energy of the fluid itself and closes automatically when flowing backwards. It is usually used at the outlet of water pump, outlet of steam trap and other places where reverse flow of fluid is not allowed. Check valves are divided into swing type, lift type and wafer type.
For swing check valves, when the flow is only from left to right, it automatically closes when the flow is reversed.
For lift check valves, when the fluid flows from left to right, the plug lifts to create a passageway, and when the fluid flows in reverse, the plug is pressed against the seat and closed.
For the wafer check valve, when the fluid flows from left to right, the valve core is opened to form a passage. When the fluid flows reversely, the valve core is pressed onto the valve seat and closed. The wafer check valve can be installed in multiple positions, with small volume, light weight and compact structure.
（3）The pressure difference between the front and rear of the control valve is certain. When the opening of the ordinary valve changes in a large range, the flow changes little. When the opening reaches a certain value, the flow changes rapidly, that is, the regulation performance is poor. The control valve can change the resistance of the valve by changing the valve core stroke according to the direction and size of the signal, so as to achieve the purpose of regulating the flow. The control valve is divided into manual control valve and automatic control valve, and the manual or automatic control valve is divided into many types, and its regulation performance is also different. Automatic control valves include self-operated flow control valves and self-operated differential pressure control valves. 
（4） Vacuum includes vacuum ball valve, vacuum baffle valve, vacuum inflation valve, pneumatic vacuum valve, etc. It is used in the vacuum system to change the direction of air flow, adjust the air flow and cut off or connect the vacuum system components called vacuum valves.
（5） Special Purpose Special purpose categories include pigging valves, vent valves, blowdown valves, vent valves, filters, etc. The exhaust valve is an indispensable auxiliary component in the pipeline system, widely used in boilers, air conditioners, oil and gas, water supply and drainage pipelines. It is usually installed at the commanding height or bend to remove excess gas in the pipeline, improve the use efficiency of the pipeline and reduce energy consumption.