■ Overview

The opening and closing component of the insulation globe valve is a plug shaped valve disc, with a flat or conical sealing surface. The valve disc moves linearly along the centerline of the fluid. The movement form of the valve stem includes a lifting rod type (the valve stem is lifted and lowered without the handwheel lifting), as well as a lifting rotating rod type (the handwheel rotates and lifts together with the valve stem, and the nut is set on the valve body). The bellows globe valve is only suitable for fully open and fully closed, and is not allowed to be adjusted or throttled. The insulation globe valve belongs to the forced sealing type valve, so when the valve is closed, pressure must be applied to the valve disc to force the sealing surface not to leak. When the medium enters valve six from below the valve disc, the resistance that the operating force needs to overcome is the frictional force between the valve stem and the packing, as well as the thrust generated by the pressure of the medium. The force required to close the valve is greater than the force required to open it, so the diameter of the valve stem should be larger, otherwise the valve stem will bend due to failure. In recent years, with the emergence of self sealing valves, the flow of medium in insulation shut-off valves has changed from above the valve disc into the valve chamber. At this time, under the pressure of the medium, the force to close the valve is small, while the force to open the valve is large, and the diameter of the valve stem can be correspondingly reduced. Meanwhile, under the influence of the medium, this type of valve is also relatively tight. The "Three Modernizations" of valves in our country have stipulated that the flow direction of insulated globe valves should be from top to bottom. When the insulation shut-off valve is opened, the opening height of the valve disc is 25% to 30% of the nominal diameter, and the flow rate has reached its maximum, indicating that the valve has reached the fully open position. So the fully open position of the shut-off valve should be determined by the stroke of the valve disc.

■ Images