Three fine knowledge of it: a flow coefficient valve <br> valve flow coefficient is a measure of the ability of the valve opening, the flow coefficient greater the pressure loss when the fluid flow through the valve is smaller. Valve manufacturers in foreign industrialized countries mostly include flow coefficient values ​​of different pressure grades, different types and different nominal diameter valves in product samples for selection by design departments and users. The flow coefficient value varies with the size, form and structure of the valve. Different types and different specifications of the valve must be tested separately to determine the flow coefficient value of the valve. Guangdong Jia Mei Biological Technology Co.Ltd , https://www.jaymeimask.com
1. Definition of flow coefficient
The flow coefficient represents the flow of fluid as it flows through the valve to produce a unit pressure loss. Due to the different units, the flow coefficient has several different codes and magnitudes.
2. Calculation of valve flow coefficient
3. Typical data of flow coefficient and factors affecting flow coefficient
Typical flow rates for various types of valves with nominal diameters of DN 50 mm are given in the table.
The flow coefficient value varies with the size, form, and structure of the valve. The flow coefficient of several typical valves varies with diameter as shown in Figure 1-9.
For valves of the same construction, the direction of fluid flow through the valve is different. The flow coefficient value also changes. This change is generally caused by different pressure recovery. If the fluid flows through the valve to cause the valve flap to open, the annular diffusion channel formed by the valve flap and the valve body can restore the pressure. When the fluid flows through the valve and the valve flap tends to close, the seat has a large effect on the pressure recovery. When the flap opening is &#+ or less, the spread angle downstream of the flap causes some pressure to recover in both flow directions.
For the high pressure angle valve shown in Figures 1-11, the flow coefficient is higher when the flow of fluid causes the valve to close, because the diffusion cone of the valve seat restores the pressure of the fluid. The geometry inside the valve is different and the curve of the flow coefficient is different.
The mechanism of pressure recovery inside the valve is the same as the pressure loss mechanism caused by the contraction and diffusion of the venturi. When the pressure drop inside the valve is the same, if the internal pressure of the valve can be recovered, the flow coefficient value will be larger and the flow rate will be larger. Pressure recovery is related to the geometry of the valve lumen, but more importantly depends on the structure of the valve flap and seat.
Second, the flow resistance coefficient of the valve <br> When the fluid passes through the valve, its fluid resistance loss is expressed by the fluid pressure drop Δp before and after the valve.
1. Fluid resistance of the valve element The coefficient of flow resistance of the valve! Depends on the size, structure and shape of the valve product. It can be considered that each component in the valve body cavity can be regarded as a component system that generates resistance (fluid turning, expansion, reduction, re-turning, etc.). Therefore, the pressure loss in the valve is approximately equal to the sum of the pressure losses of the various components of the valve.
It should be noted that a change in the resistance of a component in the system causes a change or redistribution of the resistance in the overall system, that is, the flow of the medium affects each pipe segment.
In order to assess the effect of various components on valve resistance, resistance data for some common valve components are now cited, which reflect the relationship between the shape and size of the valve components and fluid resistance.
(1) Sudden expansion will result in a large pressure loss. At this time, the velocity of the fluid portion is consumed in terms of forming eddy currents, agitation of the fluid, and heat generation. The approximate relationship between the local resistance coefficient and the ratio of the cross-sectional area A1 of the pipeline before expansion and the cross-sectional area A2 of the enlarged pipeline can be expressed by equations (1-9) and (1-10); the resistance coefficient is gradually expanded as shown in Table (2). When θ<40°C, the resistance coefficient of the gradually expanding circular tube is smaller than that when it is suddenly expanded, but when θ=50-90° C., the resistance coefficient is increased by 15%-20% more than the sudden expansion. The gradually expanding Zui has a good expansion angle θ: a circular tube θ=5-6.5 ° C, a square tube θ=7-8 ° C, and a rectangular tube 10-12 ° C.
(3) Sudden reduction (4) Gradually shrinking (5) Smooth and uniform turning (6) Corner turning Turning corner turning is mainly produced in forged valves because the medium passage of the forged valve is machined by drilling. A sharp turn can also occur in the welded valve.
(7) Symmetrical tapered joints Symmetrical tapered joints resemble valve shrinkage passages.
2. Valve fluid resistance The flow resistance coefficient of the valve varies with the type, model, size and structure of the valve.
Third, due to the pressure of the valve butterfly <br> loss in the piping pressure loss is relatively large, about three times the gate valve, butterfly valve in the choice should be considered affected by the piping system pressure loss.