Gate valve, also known as, is mainly composed of valve body, bonnet, gate, stem, valve seat and sealing packing. It is one of the most common valve types in isolation valves. The main purpose of gate valve is to cut off the fluid, which is usually called “block” valve or “block” valve. There are many different structural forms of gate valve, and the structural types of sealing elements are different. According to the structure of sealing element, it can be divided into several different types.
Classification by stem:
According to the type of stem, it can be divided into open stem gate valve and concealed stem gate valve. The valve stem is the operating part of the gate valve. Its function is to transfer the opening and closing force to the opening and closing parts.
- The trapezoidal thread of the valve stem of the rising stem gate valve is located outside the valve body and at the upper part of the valve stem. By rotating the valve stem nut, the valve stem drives the gate to rise and fall synchronously to realize the opening and closing of the valve, so it is easy to identify the opening and closing status of the valve and avoid misoperation. Because the stem nut is outside the body cavity, which is conducive to lubrication, and the opening and closing state is obvious, it is widely used. But in the bad environment, the exposed thread of the stem is easy to be damaged and corroded, and even affect the operation. Its disadvantage is that the height of the valve after opening is large, usually a stroke is added on the basis of the original height of the valve, so it needs a lot of operation space.
- The Non rising stem gate valve is also called rotary stem gate valve (also called non rising stem wedge gate valve). The stem nut is placed inside the valve body, in direct contact with the medium, and is often fixed on the gate. Through the rotation of the valve rod, the valve rod nut drives the ram to do lifting movement to complete the opening and closing. Generally, there is trapezoid thread at the bottom of the valve stem. Through the thread at the bottom of the valve and the guide groove on the valve disc, the rotary motion is changed into linear motion, that is, the operating torque is changed into the operating thrust. Since the trapezoidal thread used for transmission is located inside the valve body, susceptible to medium corrosion and unable to be lubricated, and the opening degree cannot be observed directly, an additional indicating device is required. However, the valve rod does not move up and down, so the operation space is small, so it is suitable for the occasions with limited position and dense pipeline.
According to the structure type, it can be divided into wedge gate valve and parallel gate valve. That is to say, the gate valve with wedge type is called wedge gate valve, and the gate valve with parallel type is called flat gate valve.
- The sealing surface of the flat gate valve is parallel to the vertical center line, so the sealing surface of the valve body and the gate is also parallel to each other. The most common type of gate valve is double gate plate. In order to make the sealing surfaces between the valve body and the gate close tightly, double-sided thrust wedge is often used between the two gates. Most of them are used in low-pressure pipelines such as small pipelines. There are also some parallel gate valves with single gate, but they are rare.
- Wedge gate valve is the gate valve whose sealing surface is at a certain angle with the vertical center line, i.e. two sealing surfaces are wedge-shaped. Wedge gate valve has single and double gate valves. The advantage of double gate plate is that it is sealed and the accuracy requirement of angle is low, the ram is not easy to be wedged due to the temperature change, and gasket can be added to compensate for the abrasion of sealing surface. The disadvantage is that the structure is complex, easy to stick in the dry medium, more importantly, the upper and lower baffles are easy to fall off after years of corrosion.
According to different standards: national standard gate valve, American standard gate valve, German standard gate valve and Japanese standard gate valve
According to the connection method: flange gate valve, welding gate valve, threaded gate valve (also divided into internal thread and external thread)
According to pressure rating: high pressure gate valve, low (medium) pressure gate valve
According to the driving mode: electric gate valve, pneumatic gate valve and 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 and brass gate valve), ceramic gate valve and plastic gate valve