Classification of gate valves

Gate valves have a variety of structural styles, and the main difference is that the structure type which is adopted for the sealing element. Gate valves are often divided into several types  based on the structure of the sealing element. For example, gate valves can be classified into parallel gate valves and wedge gate valves according to the type of structure. And gate valves can be divided into rising stem gate valves and non rising stem gate valves according to the structure of the valve stem.

Classification of gate valves based on valve stems
The valve stem is an operating component of the gate valve, and its function is to transmit the opening and closing force to the disc. Gate valves can be classified into rising stem gate valves and non rising stem gate valves according to the structure of the valve stem.

The trapezoidal thread of a rising stem gate valve is placed outside the valve body and is at the upper part of the valve stem. The valve stem drives the valve plate to rise and fall synchronously to open and close the gate valve by rotating the valve stem's nut. Therefore, it is easy to identify the status of the valve so as to avoid misoperation. The stem nut is outside the body cavity, which is good for lubrication. The opening and closing state of the rising stem gate valve is obvious, so it is widely used. However, the exposed threads of the rising stem gate valve are easily damaged and corroded and even affect the operation in harsh environment. 

The stem nut of non rising stem gate valve is in the valve body and is often fixed on the valve plate. The valve stem drives the valve plate to rise and fall so as to open and close the gate valve by rotating the valve stem's nut. Trapezoidal threads are in the non rising stem's valve body, which will not be influenced by the external environment, but they are not easily corroded and can't be lubricated. The stroke can not be directly observed, so there should be an indicating device. The valve stem does not move up and down, and the required operating space is small. Therefore, it is suitable for ship and underground pipes.

Classification of gate valves based on valve stems
The structure type of the gate valve usually refers to the type of the valve plate. There are two kinds of valve plates, including the wedge type and parallel type.