An Introduction to Performance of Valves

1. Sealing performance. It refers to the ability of each sealing part of valves to prevent leakage of the medium, which is the most important technical performance index of valve. The valve has three sealing positions: the contact point between the opening and closing parts and the two sealing surfaces of the valve seat, the position between packing and the valve stem and the stuffing box, the joint between the valve body and the bonnet. Among them, if the former leaks, it is called internal leakage. In other words, the valve isn't closed tightly, affecting its ability to cut off the medium. For block valves, internal leakage is not allowed. And if the last two sealing positions leak, they are called external leakage, that is, the medium leaks from inside the valve to outside the valve, which will cause material losses, pollution, and even accidents in severe cases. For flammable, explosive, toxic or radioactive media, leakage is not allowed, so the valve must have reliable sealing performance.

2. The flowing medium. After the medium flows through the valve, there will be a pressure difference between the inlet and outlet of the valve, which makes the valve have a certain resistance to the flow of the medium, and the medium will consume a certain amount of energy to overcome the resistance of the valve. Therefore, when you design and manufacture the valve, it is necessary to reduce the resistance of the valve to the flowing medium as much as possible and reduce the energy loss.

3. Opening and closing force and moments. They refer to the force or moment that must be applied to open or close the valve. When the valve is closed, it is necessary to form a certain sealing pressure between the opening and closing parts and the two sealing surfaces of the valve seat, and at the same time overcome the friction between the valve stem and other parts. Therefore, a certain closing force and moment must be exerted during the opening and closing of the valve. Strive to reduce the closing force and moment when designing and manufacturing the valve.

4. Opening and closing speed. Generally, there is no strict requirement on the opening and closing speed of valves, but some working conditions have special requirements on it, such as quick opening or closing to prevent accidents, and slow closing to prevent water hammer, which should be considered when you select valve types.

5. Service life. It represents the durability of the valve and is an important performance index of the valve, and has great economic significance. It is usually judged by the opening and closing times that can guarantee the sealing, and it can also be judged by using time.