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2020

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03

Types and classifications of gate valves

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Gate valve, also called gate valve, is mainly composed of valve body, valve cover, gate plate, valve stem, valve seat and sealing packing. It is one of the most common valve types among isolation valves. The main purpose of a gate valve is to intercept fluid, and it is for this reason that it is often called a "block" valve or a "blocking" valve. Gate valves come in many different structural forms, and they use different structural types of sealing elements. According to the structure of the sealing element, it can be divided into several different types.

Gate valve, also called gate valve, is mainly composed of valve body, valve cover, gate plate, valve stem, valve seat and sealing packing. It is one of the most common valve types among isolation valves. The main purpose of a gate valve is to intercept fluid, and it is for this reason that it is often called a "block" valve or a "blocking" valve. Gate valves come in many different structural forms, and they use different structural types of sealing elements. According to the structure of the sealing element, it can be divided into several different types.

Classification by valve stem:

According to the valve stem type, 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, and its function is to transmit the opening and closing force to the opening and closing parts.

  1. The trapezoidal thread of the valve stem of the rising stem gate valve is placed outside the valve body and located on 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 realize the opening and closing of the valve. Therefore, it is easy to identify the opening and closing of the valve. status to avoid misoperation. Since the valve stem nut is outside the body cavity, it is conducive to lubrication, and the opening and closing status is intuitive and obvious, so it is widely used. However, in harsh environments, the exposed threads of the valve stem are susceptible to damage and corrosion, even affecting operation. Its disadvantage is that the height of the valve after opening is large, and a stroke is usually added to the original height of the valve, thus requiring a large operating space . 

  2. Concealed stem gate valve is also called rotating stem gate valve (also called concealed stem wedge gate valve). The valve stem nut is placed inside the valve body, in direct 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 perform lifting movement to complete 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 disc, the rotational 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, it is susceptible to medium corrosion and cannot be lubricated. The opening degree cannot be directly observed, and an additional indicating device is required. However, its valve stem does not move up and down and requires little operating space, so it is suitable for situations with limited positions and dense pipelines. 

    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 wedge gate valve, and if the gate plate is parallel type, it is called flat gate valve.

  1. The sealing surface of the flat gate valve is parallel to the vertical center line, so the sealing surfaces of the valve body and the gate plate are also parallel to each other. The most common type of this kind of gate valve is the double gate plate type. In order to ensure tight contact between the two sealing surfaces of the valve body and the gate plate when closing, a double-sided thrust wedge is often used between the two gate plates. Mostly used in low-pressure pipelines such as small pipelines. There are also parallel gate valves that use a single gate plate, but they are rare. 

  2. Wedge gate valve is a gate valve in which the sealing surface is at a certain angle with the vertical centerline, that is, the two sealing surfaces are wedge-shaped. Wedge gate valves have single or double gate plates. The advantage of the double gate type is that the sealing and angle accuracy requirements are low, temperature changes are not easy to cause the gate to wedge, and gaskets can be added to compensate for sealing surface wear. The disadvantage is that the structure is complex and easy to stick in dry media. More importantly, the gate plate is easy to fall off after the upper and lower baffles are rusted for many years. 

    Other ways to classify:

    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 driving mode: electric gate valve , pneumatic gate valve , manual gate valve

    Classified 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