Special valves are unconventional valves. The valves we often use include: wafer butterfly valve, medium-sized double flange butterfly valve, double eccentric butterfly valve, three-dimensional eccentric butterfly valve, expansion butterfly valve, ventilation butterfly valve, check valve butterfly valve, double flange sleeve expansion device, double flange loose sleeve expansion device, double flange limit expansion device, double flange force transmission expansion device, flexible rubber expansion device, compensator, gate valve, gate valve Exhaust valve, stop valve, etc.
Introduction to special valves
1、 Characteristics of gate valve:
Gate valve refers to the valve whose gate moves vertically along the center line of the channel. The gate valve is mainly used to cut off the pipeline. Gate valve is a widely used valve, which is generally used for the cut-off device with diameter DN ≥ 50mm, and sometimes for the cut-off device with small diameter. Gate valves have the following advantages:
① Low fluid resistance.
② The external force required for opening and closing is small.
③ The flow of media is unlimited.
④ When fully open, the erosion of the working medium on the sealing surface is less than that of the stop valve. ⑤ The shape is relatively simple and the casting process is good.
Gate valves also have disadvantages:
① The overall dimension and opening height are large. The required installation space is large.
② During the opening and closing process, there is relative friction between the sealing surfaces, which is easy to cause wear.
③ The gate valve generally has two sealing surfaces, which makes it difficult to process, grind and maintain.
2、 Classification of gate valves:
1. according to the structure of the ram, it can be divided into
1) Parallel gate valve: the sealing surface is parallel to the vertical center line, that is, the two sealing surfaces are parallel to each other.
In parallel gate valves, there are single gate valves and double gate valves with thrust wedges. It is common that since there are double thrust wedges between the two rams, this kind of gate valve is suitable for low and medium pressure (dn40-300mm) gate valves. There is also a spring between the two rams, which can generate pre tightening force, which is conducive to the sealing of the rams.
2) Wedge gate valve: the sealing surface forms a certain angle with the vertical center line, that is, the two sealing surfaces are wedge gate valves. The inclination angle of the sealing surface is generally 2 ° 52 °, 3 ° 30 °, 5 °, 8 °, 10 °, etc. The angle mainly depends on the temperature of the medium. Generally speaking, the higher the operating temperature, the greater the angle should be, so as to reduce the possibility of wedging in case of temperature change.
2. according to the structure of the valve stem, the gate valve can be divided into
1) Rising stem gate valve: the stem nut is on the bonnet or bracket. When opening and closing the gate, rotate the valve rod nut to lift the valve rod. This structure is conducive to the lubrication of the valve rod, and the opening and closing degree is obvious, so it is widely used.
2) Non rising stem gate valve: the valve stem nut is in the valve body and in direct contact with the medium. This is achieved by rotating the valve stem when the gate is opened and closed. The advantage of this structure is that the height of the gate valve is always the same, so the installation space is small. It is suitable for gate valves with large diameter or limited installation space. The structure shall be equipped with an opening and closing indicator to indicate the degree of opening and closing. The disadvantage of this structure is that the valve rod thread is not only not lubricated, but also directly corroded by the medium and easy to be damaged.