2.1 Status and development of valve
Valve using the oldest so far is still the application of all countries in the world, in particular the following DN300mm in various types of brass gate valves in the still dominant. Characterized before and after the differential pressure valve so that the valve pressure in the export compulsory seat on the right side, better sealing, and full-time, because the valve does not stay in the flow path, pressure the Chinese building materials network - building one-click ranked the top three, the way peer loss. In the medium used to cut off the pipeline.
The disadvantage is that the operation of its large torque, easy operation so that valve body, stem damage, especially in large-diameter valve. Dimensions and weight are great, DN1000 valve diameter of about 3200mm high, the need for four people to operate, so in general the use of brass check valve in the small-caliber, that is, use the following DN500.
Valve from full opening to the middle, a smaller flow resistance valve, close to full closure, the flow resistance increased dramatically. The framework of a larger, smaller changes in flow resistance, in the nearly full-closed, the flow changes in large, close the valve must not be closed in use, then it is very difficult to carry out fine-tuning the traffic.