The valve is used for cutting off the medium. When fully open, the entire flow is straight through, and at this time, the pressure loss of the medium operation is minimal. Valves are usually suitable for situations where they do not need to be opened or closed frequently, maintaining the condition of the gate being fully open or fully closed. They are not suitable for use as regulators or throttles. For high-speed flowing media, the gate can cause vibration when partially open, and this vibration may damage the sealing surface of the gate and the valve seat, while throttling can cause erosion on the gate. In terms of structural form, the main difference lies in the form of the sealing element used. Based on the form of the sealing element, valves are often divided into several different types, such as wedge gate valves, parallel gate valves, double-disc parallel gate valves, wedge double-disc gates, etc. The most commonly used forms are wedge gate valves and parallel gate valves. This type of valve's function is to only allow the medium to flow in one direction and prevent reverse flow. These valves typically work automatically; under the pressure of fluid flowing in one direction, the valve disc opens; when the fluid flows in the reverse direction, the fluid pressure and the weight of the valve disc act together on the valve seat, thereby cutting off the flow. Among these, check valves belong to this type of valve, including swing check valves and lift check valves. A swing check valve has a hinge mechanism, with a valve disc that freely leans against an inclined valve seat like a door. To ensure that the valve disc reaches the correct position on the valve seat each time, it is designed with a hinge mechanism so that the valve disc has sufficient swing space and truly makes full contact with the valve seat. The valve disc can be entirely made of metal, or it can have leather or rubber embedded on metal, or use synthetic coatings, depending on the requirements of usage performance. Under fully open conditions, the fluid pressure in a swing check valve is almost unobstructed, so the pressure drop through the valve is relatively small. In a lift check valve, the valve disc rests on the sealing surface of the valve seat inside the valve body. Apart from the valve disc being able to move freely up and down, the rest is similar to a globe valve. Fluid pressure lifts the valve disc off the sealing surface of the valve seat; medium backflow causes the valve disc to fall back onto the valve seat and cut off the flow. Depending on the usage conditions, the valve disc can be all-metallic construction or have rubber pads or rings embedded on a valve disc frame. Like a globe valve, the passage through which fluid flows in a lift check valve is narrow, so the pressure drop through a lift check valve is greater than that of a swing check valve, and the flow restriction in a swing check valve is minimal. During the production process, to make parameters such as the pressure and flow rate of the medium meet the requirements of the process, a regulating mechanism needs to be installed to adjust these parameters. The main working principle of the regulating mechanism is to change the flow area between the valve disc and the valve seat of the valve to achieve the purpose of adjusting these parameters. Such valves are collectively referred to as control valves, among which those driven by the inherent power of the medium are called self-driven control valves, such as relief valves and pressure stabilizing valves, etc., while those driven by external power (such as electricity, compressed air, and hydraulic power) are called externally driven control valves, such as electric control valves, pneumatic control valves, and hydraulic control valves, etc.