According to function and role

(I) Shut-off valve

This valve is used to open and close. Permanently installed on the inlet and outlet of cold and heat sources, equipment inlet and outlet, and branch lines of pipelines (including standpipes), and can also be used as drain valves and exhaust valves. Commonly used globe valves include gate valve, globe valve, ball valve and butterfly valve. Gate valve can be divided into open rod and dark rod, single gate and double gate, wedge gate and parallel gate, etc. The closing tightness of the gate valve is good, and the small diameter gate valve is difficult to open; the valve body is large in size along the water flow direction, the flow resistance is large, and the nominal diameter span of the gate valve is small. According to the flow direction of the medium, the globe valve is divided into three types: straight-through, right-angle and direct-flow Type, divided into open rod and dark rod. The closing air tightness of the globe valve is better than that of the gate valve. The valve body is long and the flow resistance is small. The valve core of the ball valve with the minimum nominal diameter of DN200 is a ball with a hole. Turn the valve stem so that the opening of the ball is facing the axis of the pipe, the pipe is in a fully open state, and turn it 90° to make it in a fully closed state. The ball valve has a certain adjustment performance, and the valve core of the closed butterfly valve is a circular valve plate, which can rotate along the vertical axis perpendicular to the pipeline axis. When the plane of the valve plate is the same as the axis of the pipeline, the valve plate is in a fully open state; when the plane of the gate plate is perpendicular to the axis of the pipeline, the valve plate is completely closed. Butterfly valve has large body length and large flow resistance, which is higher than the price of gate valve and globe valve.

(II) Check valve

This valve is used to prevent backflow of media. It opens on its own using the kinetic energy of the fluid and closes automatically when the flow is reversed. Stand at pump outlets, trap outlets, and other locations 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 fluid can only flow from left to left, it will automatically close when fluid flows in the opposite direction. For poppet check valves, when the fluid flows from left to left, the spool is lifted to form a channel, and when the fluid flows in the opposite direction, the spool is pressed over the valve seat and closed. For a wafer check valve, when fluid flows from left to left, the spool opens to form a path, and when the flow is reversed, the spool presses against the seat and closes. Wafer-type check valves can be installed in multiple locations and are bulky, slow, and compact.

(III) Regulating valve

The pressure difference between the left and right of the valve is determined. When the opening of the general valve changes within a small range, the flow change is not small, but when it reaches a certain opening, the flow changes drastically, that is, the adjustment performance is less. The regulating valve can change the resistance number of the valve by changing the stroke of the spool according to the direction and size of the signal, so as to achieve the purpose of regulating the flow. The regulating valve is divided into manual regulating valve and automatic regulating valve. There are many kinds of manual or automatic regulating valve, and their regulating performance is also different. Automatic regulating valve includes self-operated flow regulating valve and self-operated differential pressure regulating valve