Gate valve, also known as gate valve, is mainly composed of valve body, valve cover, gate plate, valve stem, valve seat and sealing packing. It is one of the common types of valves in isolation valves. The main purpose of the gate valve is to cut off the fluid. For this reason, it is often called the "cut-off" valve or "blocking" valve. There are many different structural forms of gate valves, and the structure types of sealing elements used are different. According to the structure of the sealing element, it can be divided into several different types. 

 I. Classification according to the valve stem: 

 According to the stem type, it can be divided into open rod gate valve and hidden rod gate valve. The stem is the operating part of the gate valve, and its function is to transmit the opening and closing force to the opening and closing part. 

 1. The trapezoidal thread of the valve stem of the clear stem gate valve is placed outside the valve body and is located in the upper part of the valve stem. By rotating the valve stem nut, the valve stem drives the gate plate to rise and fall synchronously to achieve the opening and closing of the valve, so it is easy to identify the opening and closing state of the valve and avoid misoperation. Because the valve stem nut is outside the cavity, it is conducive to lubrication, and the opening and closing state is intuitive and obvious, so it is widely used. However, in harsh environments, the exposed thread of the valve stem is vulnerable to damage and corrosion, and even affects the operation. Its disadvantage is that the height of the valve is large after opening. Usually, a stroke is added to the original height of the valve, so it requires a large operating space. 

 2. The dark rod gate valve is also known as the rotary rod gate valve (also known as the hidden rod wedge gate valve). The stem nut is placed inside the valve body, directly in contact with the medium, and is often fixed on the gate plate. Through the rotation of the valve stem, the valve stem nut drives the gate plate to lift and close to complete the opening and closing. Usually, there is a trapezoidal thread at the bottom of the valve stem. Through the thread at the bottom of the valve and the guide groove on the valve flap, the rotational movement is changed into a linear movement, that is, the operating torque is changed to the operating thrust. Because the trapezoidal thread for transmission is inside the valve body, it is susceptible to medium corrosion and cannot be lubricated. The degree of opening cannot be directly observed, and a separate indication device needs to be set up. However, its valve stem does not move up and down, and the operating space required is small, so it is suitable for occasions where the position is limited and the pipeline is dense. 

 II. Classification by structure: 

 According to the structure type, it can be divided into two types: wedge gate valve and parallel gate valve. That is, if the gate plate is wedge-type, it is called a wedge gate valve, and if the gate plate is parallel, it is a flat gate valve. 

 1. The flat gate valve means that the sealing surface is parallel to the vertical center line, so the valve body and the sealing surface on the gate plate are also parallel to each other. This kind of gate valve is commonly double gate plate type. In order to make the valve body and the two sealing surfaces of the gate plate in close contact when closed, double-sided thrust wedges are often clamped between the two gate plates. It is mostly used in low-pressure pipelines such as small pipelines. There are also parallel gate valves with single gate plates, but they are rare. 

 2. The wedge gate valve is a gate valve with a certain angle between the sealing surface and the vertical center line, that is, a wedge-shaped gate valve with two sealing surfaces. There are single and double gate plates of wedge gate valves. The advantage of the double gate plate type is that it is sealed and the accuracy requirements of the angle are low. The temperature change is not easy to make the gate wedged, and the wear of the sealing surface can be compensated by gaskets. The disadvantage is that the structure is complex, easy to stick in the dry medium, and the gate is easy to fall off after the upper and lower baffles are rusted for a long time. 

 III. Classification in other ways: 

 According to different standards: national standard gate valve, American standard gate valve, German standard gate valve, Japanese standard gate valve 

 According to the connection method: flange gate valve, welded gate valve, threaded gate valve (also divided into internal thread and external thread) 

 According to pressure level: high-pressure gate valve, low (medium) pressure gate valve 

 According to the drive mode: electric gate valve, pneumatic gate valve, manual gate valve 

 Classification by material: stainless steel gate valve, forged steel gate valve, cast steel gate valve, carbon steel gate valve, cast iron gate valve, copper gate valve (also divided into bronze gate valve, brass gate valve), ceramic gate valve, plastic gate valve