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1、阀门流量计算方法如何使用流量系数How to use Cv阀门流量系数(Cv)是表示阀门通过流体能力的数值。Cv越大，在给定压降下阀门能够通过的流体就越多。Cv值1表示当通过压降为1 PSI时，阀门每分钟流过1加仑15oC的水。Cv值350表示当通过压降为1 PSI时，阀门每分钟流过350加仑15oC的水。Valve coefficient (Cv) is a number which represents a valves ability to pass flow. The bigger the Cv, the more flow a valve can pass with a given
2、pressure drop. A Cv of 1 means a valve will pass 1 gallon per minute (gpm) of 60oF water with a pressure drop (dp) of 1 PSI across the valve. A Cv of 350 means a valve will pass 350 gpm of 60oF water with a dp of 1 PSI.公式1FORMULA 1流速：磅/小时(蒸汽或水)FLOW RATE LBS/HR (Steam or Water)在此：Where:dp=压降，单位：PSIdp
3、=pressure drop in PSIF=流速，单位：磅/小时F=flow rate in lbs./hr.=比容积的平方根，单位：立方英尺/磅(阀门下游)=square root of a specific volume in ft3/lb.(downstream of valve)公式2FORMULA 2流速：加伦/分钟(水或其它液体)FLOW RATE GPM (Water or other liquids)在此：Where:dp=压降，单位：PSIdp=pressure drop in PSISg=比重Sg=specific gravityQ=流速，单位：加伦/分钟Q=flow r
4、ate in GPM局限性LIMITATIONS上列公式在下列条件下无效：Above formulas are not valid under the following conditions:a. 对于可压缩性流体，如果压降超过进口压力的一半。For compressible fluids, where pressure drop exceeds half the inlet pressure. b. 对于不可压缩性流体，如果压降产生空穴或闪蒸。For non-compressible fluids, where pressure drop causes cavitation or flas
5、hing. c. 对于双相流体，如蒸汽-水混合流体。For dual-phase flow such as steam-water mixtures. 例子EXAMPLE1. 通过DN350, 压力等级Class 900的压力密封闸阀，水温400oF，压力为1500 PSIG，流速为5,000,000磅/小时的压降是多少？What is the pressure drop through a 14 Class 900 pressure seal gate valve with 400oF water, 1500 PSIG, and 5,000,000 lbs/hr flow rate?解：采用
6、公式1Solution: Use formula 1. F=5,000,000=0.137 (从水温为400oF的表中得到)=0.137 (from chart for water at 400oF)Cv=9150 (来自本页)Cv=9150 (from page 26)2. DN350 x DN300 x DN350，压力等级Class 900缩喉管压力密封闸阀，其它条件与例1相同，求压降。What is the pressure drop through a 14x12x14 Class 900 Venturi pressure seal gate valve with the same
7、conditions as example 1.解：采用公式1Solution: Use formula 1.Cv = 6285 (来自本页)Cv = 6285 (from page 26)3. 温度900oF, 压力1200 PSI，流速500,000磅/小时的蒸汽应用中压降小于5 PSI的压力等级Class 2500闸阀的最小通径是多少？What is the smallest Class 2500 gate valve that will have less than a 5 PSI pressure drop in 900oF, 1200 PSI steam service at a
8、flow rate of 500,000 lbs/hr?解：采用公式1Solution: Use formula 1. F=500,000=0.785 (来自900oF, 1200 PSIG蒸汽表)=0.785 (from chart for steam at 900oF, 1200 PSIG)= 2.24最接近的、较大的Cv是DN250压力等级Class 2500闸阀，其Cv是3130。这里是压降小于5 PSIG的最小的阀门。The closest higher Cv is a 10 Class 2500 gate with a Cv of 3130. This is the smalles
9、t valve with a pressure drop less than 5 PSIG.水和蒸汽的备选特性Selected Properties of Water and Steam水的(下游)For Water (Downstream)所有压力等级AllPressures温度(oF)Temperature (oF)1002003004005006000.1270.1290.1320.1370.1430.154蒸汽的(下游)For Steam (Downstream)压力PSIG PressurePSIG温度(oF)Temperature (oF)Sat500600700800900100
10、0110010020030040050060070080090010001100120013001400160018002000250030004000500060001.971.461.211.060.9500.8650.8010.7470.7010.6620.6280.5980.5700.5452.201.611.301.110.9790.8952.321.681.381.191.060.9600.8800.8150.7590.7100.6700.6290.5900.5592.441.771.461.261.121.020.9410.8750.8210.7730.7320.6950.662
11、0.6330.580.540.500.410.310.170.160.162.541.851.521.321.181.080.9940.9260.8700.8160.7810.7450.7100.6830.630.590.550.480.420.320.240.192.641.951.601.381.231.131.040.9720.9140.8650.8230.7850.7520.7230.670.630.590.520.460.380.320.282.742.001.651.431.281.171.081.010.9550.9170.8720.8130.7890.7520.700.660.
12、620.550.490.420.360.322.842.071.711.471.331.221.121.050.990.940.900.860.830.790.740.690.650.580.520.440.390.35阀座端口流速计算Calculating Seat Port Velocity下列公式可以用来计算任何阀门的阀座流速：The following formulas can be used to calculate seat portvelocity in any valve:流量(磅/小时): 流速: (英尺/秒)= F()225AFlow (lbs/hr): vel: (fps
13、) = F()225A流量(加仑/分钟): 流速: (英尺/秒)= 0.32QAFlow (GPM): vel: (fps) = 0.32QA在此：Where:F=流量(磅/小时)F=flow (lbs/hr)=比容积的平方根=square root of specific volumeA=阀座端口面积 (英寸2)A=seat port area (in2)Q=流量 (加仑/分钟)Q=flow (gpm)例：DN300型号58809 (压力等级Class 900)止回阀，流体介质为温度500 oF，压力200 PSIG的蒸汽，流速为90,000磅/小时，求阀座端口的流速？ Example:What is the seat port velocity in a 12 Figure 58809 (Class 900) check valve with a flow rate of 90,000 lbs/hr of steam at 500 oF and 200 PSIG?解：从蒸汽表得为1.61，从阀座端口面积表A得阀座端口面积为78.5英寸2。Answer:From the steam tables is 1.61, and from the seat port area table A is 78.5 in2.流速: (英尺/秒)= F
