Threaded valve has the following advantages: simple structure, manufacture and maintenance more convenient. Working stroke is small, open and close a short time. Sealing, the sealing surface between the friction force is small, longer life expectancy. Threaded valve defects are as follows: fluid resistance, force required to open and close more. Does not apply with particles, viscosity, easy to medium coke. Regulation performance is poor. The type of threaded valve stem according to the position of sub-threads are male, and internal threaded. Divided by the flow medium, with straight-through, DC type and angle type. The form of points according to the sealing valve, a fill valve and bellows bellows seal valves. Threaded valve installation and maintenance should note the following: hand wheel, lever operated bellows valve in the pipe can be installed in any position. Hand wheels, handles and Wai actuator, does not allow for lifting purposes. Medium as shown in the flow direction of the arrow should be consistent with the body. Threaded valve, also called cut-off doors, is the most widely used as a valve, which popular reason is because the process of opening and closing the friction between the sealing surface is small, more durable, opening height is not to create easy, easy maintenance, not only for low pressure, but also for hypertension. Its principle is closed, relying on the valve bar pressure, so that valve sealing surface and valve seat sealing surface tightly, to prevent media flow. Threaded valve can only way media flow direction when installing. Its structure is greater than the gate length, while the fluid resistance, long-term operation, the sealing reliability is not strong. Threaded valve is divided into three categories: straight-through, angled and DC-type oblique cut-off valve. Threaded valve is open, the valve opening height, the nominal diameter of 25% to 30%, the flow has reached the maximum that the valve has reached the fully open position. Therefore, valve fully open position, valve stroke should be determined.