The shut-off valve, also known as the ball valve, is a forced-sealed valve, so when the valve is closed, pressure must be applied to the valve flap to force the sealing surface to leak. When the medium enters the valve from below the valve flap, the resistance to be overcome by the operating force is the friction between the 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 stem The diameter of the stem should be large, otherwise the valve stem can be bent. There are three types according to the connection method: flange connection, thread connection, and welding connection.

In recent years, after the appearance of the self-sealing valve, the medium flow direction of the shut-off valve is changed from the valve flap to the valve chamber. At this time, under the action of the medium pressure, the force to close the valve is small, and the force of opening the valve is large, the valve stem 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. When the valve is to be installed horizontally, the opening height of the valve flap is 25% to 30% of the nominal diameter. The flow rate has reached the maximum, 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.

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