Technical principle: When the internal thread gate valve is opened, the opening height of the valve flap is 25% to 30% of the nominal diameter, and the flow rate has reached a large value, indicating that the valve has reached the fully open position. Therefore, the full open position of the shutoff valve should be determined by the stroke of the valve flap.
Internal thread gate valves, high pressure gate valves, and tube stop valves are mandatory seal valves, so when the valve is closed, pressure must be applied to the valve flap to force the seal face to leak. When the medium enters the valve six from below the valve flap, the resistance to be overcome by the operating force is the friction force of the valve stem and the packing and the thrust generated by the pressure of the medium. The force of closing the valve is greater than the force of opening the valve, so the valve The diameter of the rod is large, otherwise the valve stem will be bent. In recent years, after the appearance of the self-sealing valve, the medium flow direction of the shut-off valve is changed into the valve chamber from above the valve flap. At this time, under the action of the medium pressure, the force of closing the valve is small, and the force of opening the valve is large, the valve stem is The diameter can be reduced accordingly. At the same time, this type of valve is also tight under the action of the medium. China's valve "three-way to give" has stipulated that the flow of the stop valve, all from top to bottom.
advantage:
The structure is simple, and the manufacturing and maintenance are convenient.
The working schedule is small and the opening and closing time is short.
The sealing performance is good, the friction between the sealing surfaces is small, and the service life is long.
Disadvantages:
The fluid resistance is large, and the force required to open and close is large.
Not suitable for media with particles, high viscosity, and easy to coke.
Poor adjustment performance.
The type of internal thread gate valve is divided into external thread type and internal thread type according to the position of the stem thread. According to the flow direction of the medium, there are straight-through, direct-current and angular. The shut-off valve is divided into sealed forms, with a packing bellows gate valve and a bellows sealing globe valve.
Internal thread gate valves, high pressure gate valves, and tube stop valves are mandatory seal valves, so when the valve is closed, pressure must be applied to the valve flap to force the seal face to leak. When the medium enters the valve six from below the valve flap, the resistance to be overcome by the operating force is the friction force of the valve stem and the packing and the thrust generated by the pressure of the medium. The force of closing the valve is greater than the force of opening the valve, so the valve The diameter of the rod is large, otherwise the valve stem will be bent. In recent years, after the appearance of the self-sealing valve, the medium flow direction of the shut-off valve is changed into the valve chamber from above the valve flap. At this time, under the action of the medium pressure, the force of closing the valve is small, and the force of opening the valve is large, the valve stem is The diameter can be reduced accordingly. At the same time, this type of valve is also tight under the action of the medium. China's valve "three-way to give" has stipulated that the flow of the stop valve, all from top to bottom.
advantage:
The structure is simple, and the manufacturing and maintenance are convenient.
The working schedule is small and the opening and closing time is short.
The sealing performance is good, the friction between the sealing surfaces is small, and the service life is long.
Disadvantages:
The fluid resistance is large, and the force required to open and close is large.
Not suitable for media with particles, high viscosity, and easy to coke.
Poor adjustment performance.
The type of internal thread gate valve is divided into external thread type and internal thread type according to the position of the stem thread. According to the flow direction of the medium, there are straight-through, direct-current and angular. The shut-off valve is divided into sealed forms, with a packing bellows gate valve and a bellows sealing globe valve.
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