Ascending Efficiency: Rising Stem Valves in Critical Process Control
Nov 21,2023Read More
Gate valve is mainly composed of valve body, bonnet, gate plate, valve stem, valve seat and sealing packing. It is one of the common valve types in isolation valves. The main purpose of a gate valve is to shut off fluid, and it is for this reason that it is often called a "block" valve. There are many different structural forms of gate valves, and the types of sealing elements used in them are different. According to the structure of the sealing element, it can be divided into several different types.
According to the stem type, it can be divided into rising stem gate valve and dark 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, on the upper part of the valve stem. By rotating the stem nut, the valve stem drives the gate plate to rise and fall synchronously to realize the opening and closing of the valve, so it is easy to identify the valve The opening and closing state to avoid misuse. Because the valve stem nut is outside the body cavity, it is beneficial to lubrication, and at the same time, the opening and closing state is intuitive and obvious, so it is widely used. However, in harsh environments, the exposed threads of the valve stem are vulnerable to damage and corrosion, and even affect the 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) Dark stem gate valve is also called rotary stem gate valve (also known as dark 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 plate. Through the rotation of the valve stem, the valve stem nut drives the gate plate to move up and down to complete the opening and closing. Usually there is a trapezoidal thread at the bottom of the valve stem, and through the threads at the bottom of the valve and the guide groove on the valve clack, the rotating motion is changed into a straight line motion, that is to say, the operating torque is changed into the operation thrust. Since the trapezoidal thread for transmission is located inside the valve body, it is easily corroded by the medium 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 the required operating space is small, so it is suitable for occasions with limited locations and dense pipelines.
According to the structure type, gate valve can be divided into wedge gate valve and parallel gate valve. That is, the wedge-type gate valve is called wedge gate valve, and the parallel gate valve 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. This kind of gate valve is usually of the double gate type. In order to make the valve body and the two sealing surfaces of the gate tightly contact when closing, a double-sided thrust wedge is often used between the two gates. It is mostly used on low-pressure pipelines such as small pipelines. There are also parallel gate valves with single gate, but they are rare.
(2) Wedge gate valve is a gate valve in which the sealing surface is at a certain angle to the vertical centerline, that is, the two sealing surfaces are wedge-shaped. Wedge gate valves have both single and double gates. The advantage of the double ram type is that the accuracy of the angle of the sealing surface is relatively low, the temperature change is not easy to cause the ram to be wedged, and the wear of the sealing surface can be compensated by adding gaskets. The disadvantage is that the structure is complex, and it is easy to stick in the viscous medium. What's more, the gate plate is easy to fall off after the upper and lower baffles have been rusted for many years.
(1) According to different standards: national standard gate valve, American standard gate valve, German standard gate valve, Japanese standard gate valve.
(2) According to the connection method: flanged gate valve, welded gate valve, threaded gate valve (also divided into internal thread and external thread).
(3) Pressure level: high pressure gate valve, low (medium) pressure gate valve.
(4) According to the driving mode: electric gate valve, pneumatic gate valve, manual gate valve.
(5) 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.
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