The shut-off valve is used to open completely or completely. According to their function, can not be used as a throttling. In this case, an accident may occur due to the violent vibration of the medium, which may damage the flapper of the flash valve. However, the throttle valve flap design, to consider the need to completely close the incense seal performance. The following data on globe valve hydraulic characteristics apply to accurate drive power calculations and can also be used in the identification of closed-circuit valves. In the cut-off valve, the size of the open cross-sectional area Ak depends on the structure of the valve flap and its opening height on the valve seat. If the plane seal, the size of the open area can be approximated by the following formula: Ak = πDch If the cone disc (needle valve, see Figure 3-142c), can be calculated as Ak = π (Dc- hsinαcosα) hsinα The chamfered planar disc is, in terms of its shape, between plane and conical. If the valve opening height is very small, the bottom of the valve is not higher than the seat surface above the cone valve can be used formula; if the opening height is large, Ak value close to the flat seal valve flap determined by the data , Then the valve opening height should be calculated according to the distance between the valve flap bottom and the valve seat surface. DN25mm globe valve fluid resistance, depending on the valve flap from the valve opening height.
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