阀门流量计算方法

阀门流量计算方法如何使用流量系数HowtouseCv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1PSI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1PSI时，阀门每分钟流过350加仑15oC的水。Valvecoefficient(Cv)isanumberwhichrepresentsavalve'sabilitytopassflow.ThebiggertheCv,themoreflowavalvecanpasswithagivenpressuredrop.ACvof1meansavalvewillpass1gallonperminute(gpm)of60oFwaterwithapressuredrop(dp)of1PSIacrossthevalve.ACvof350meansavalvewillpass350gpmof60oFwaterwithadpof1PSI.公式1FORMULA1流速：磅/小时(蒸汽或水)FLOWRATELBS/HR(SteamorWater)在此：Where:dp=压降，单位：PSIdp=pressuredropinPSIF=流速，单位：磅/小时F=flowrateinlbs./hr.=比容积的平方根，单位：立方英尺/磅(阀门下游)=squarerootofaspecificvolumeinft3/lb.(downstreamofvalve)公式2FORMULA2流速：加伦/分钟(水或其它液体)FLOWRATEGPM(Waterorotherliquids)在此：Where:dp=压降，单位：PSIdp=pressuredropinPSISg=比重Sg=specificgravityQ=流速，单位：加伦/分钟Q=flowrateinGPM局限性LIMITATIONS上列公式在下列条件下无效：Aboveformulasarenotvalidunderthefollowingconditions:a.对于可压缩性流体，如果压降超过进口压力的一半。Forcompressiblefluids,wherepressuredropexceedshalftheinletpressure.b.对于不可压缩性流体，如果压降产生空穴或闪蒸。Fornon-compressiblefluids,wherepressuredropcausescavitationorflashing.c.对于双相流体，如蒸汽-水混合流体。Fordual-phaseflowsuchassteam-watermixtures.例子EXAMPLE1.通过DN350,压力等级Class900的压力密封闸阀，水温400oF，压力为1500PSIG，流速为5,000,000磅/小时的压降是多少？Whatisthepressuredropthrougha14Class900pressuresealgatevalvewith400oFwater,1500PSIG,and5,000,000lbs/hrflowrate?解：采用公式1Solution:Useformula1.F=5,000,000=0.137(从水温为400oF的表中得到)=0.137(fromchartforwaterat400oF)Cv=9150(来自本页)Cv=9150(frompage26)2.DN350xDN300xDN350，压力等级Class900缩喉管压力密封闸阀，其它条件与例1相同，求压降。Whatisthepressuredropthrougha14x12x14Class900Venturipressuresealgatevalvewiththesameconditionsasexample1.解：采用公式1Solution:Useformula1.Cv=6285(来自本页)Cv=6285(frompage26)3.温度900oF,压力1200PSI，流速500,000磅/小时的蒸汽应用中压降小于5PSI的压力等级Class2500闸阀的最小通径是多少？WhatisthesmallestClass2500gatevalvethatwillhavelessthana5PSIpressuredropin900oF,1200PSIsteamserviceataflowrateof500,000lbs/hr?解：采用公式1Solution:Useformula1.F=500,000=0.785(来自900oF,1200PSIG蒸汽表)=0.785(fromchartforsteamat900oF,1200PSIG)==2.24最接近的、较大的Cv是DN250压力等级Class2500闸阀，其Cv是3130。这里是压降小于5PSIG的最小的阀门。TheclosesthigherCvisa10Class2500gatewithaCvof3130.Thisisthesmallestvalvewithapressuredroplessthan5PSIG.水和蒸汽的备选特性SelectedPropertiesofWaterandSteam水的(下游)ForWater(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)ForSteam(Downstream)压力PSIGPressurePSIG温度(oF)Temperature(oF)Sat50060070080090010001100100200300400500600700800900100011001200130014001600180020001.971.461.211.060.9500.8650.8010.7470.7010.6620.6280.5980.5700.5452.201.611.301.110.9790.8952.321.681.381.191.060.9600.8800.8150.7590.7100.6700.6290.5900.5592.441.771.461.261.121.020.9410.8750.8210.7730.7320.6950.6620.6330.580.540.502.541.851.521.321.181.080.9940.9260.8700.8160.7810.7450.7100.6830.630.590.552.641.951.601.381.231.131.040.9720.9140.8650.8230.7850.7520.7230.670.630.592.742.001.651.431.281.171.081.010.9550.9170.8720.8130.7890.7520.700.660.622.842.071.711.471.331.221.121.050.990.940.900.860.830.790.740.690.65250030004000500060000.410.310.170.160.160.480.420.320.240.190.520.460.380.320.280.550.490.420.360.320.580.520.440.390.35阀座端口流速计算CalculatingSeatPortVelocity下列公式可以用来计算任何阀门的阀座流速：Thefollowingformulascanbeusedtocalculateseatportvelocityinanyvalve:流量(磅/小时):流速:(英尺/秒)=F()225AFlow(lbs/hr):vel:(fps)=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=squarerootofspecificvolumeA=阀座端口面积(英寸2)A=seatportarea(in2)Q=流量(加仑/分钟)Q=flow(gpm)例：DN300型号58809(压力等级Class900)止回阀，流体介质为温度500oF，压力200PSIG的蒸汽，流速为90,000磅/小时，求阀座端口的流速？Example:Whatistheseatportvelocityina12Figure58809(Class900)checkvalvewithaflowrateof90,000lbs/hrofsteamat500oFand200PSIG?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:Fromthesteamtablesis1.61,andfromtheseatportareatableAis78.5in2.流速:(英尺/秒)=F()225A=90,000(1.61)225(78.5)=118.8英尺/秒Vel(fps)=F()225A=90,000(1.61)225(78.5)=118.8fps例：DN300型号180(压力等级150)旋启式止回阀，流体介质为温度500oF，压力200PSIG的蒸汽，流速为90,000磅/小时，求阀座端口流速？Example:Whatistheseatportvelocityina12Figure180(Class150)SwingCheckValvewithaflowrateof90,000lbs/hrofsteamat500oFand200PSIG?解：查表得为1.61，A为113.1英寸3.Answer:Fromthetablesis1.61andAis113.1in3.流速:(英尺/秒)=F()225A=90,000(1.61)225(113.1)=82.5英尺/秒Vel(fps)=F()225A=90,000(1.61)225(113.1)=82.5fps局限性LIMITATIONS流速公式在下列条件下无效：Velocityformulasarenotvalidunderthefollowingconditions:a.对于可压缩性流体，如果压降超过进口压力的一半。Forcompressiblefluids,wherepressuredropexceedshalftheinletpressure.b.对于不可压缩性流体，如果压降产生空穴或闪蒸。Fornon-compressiblefluids,wherepressuredropcausescavitationorflashing.c.对于双相流体，如蒸汽-水混合流体。Fordual-phaseflowsuchassteam-watermixtures.注意NOTE在确定止回阀通径时，最适宜的工作流速应该位于这些范围内：Whendeterminingsizingforcheckvalves,theoptimumoperatingvelocitiesshouldfallwithintheseranges:BB旋启式止回阀：55至115或135至240BB截止止回阀：40至120PS提升式阀瓣止回阀：55至200PSY形止回阀：148至200BBSwingCheckValves-55to115or135to240BBStopCheckValves-40to120PSTiltDiscCheckValves-55to200PSStopCheckValves-40to180PSY-StopCheckValves-148to200阀座端口面积“A”(英寸2)适用于螺栓阀帽阀门SEATPORTAREAAFORBOLTEDBONNETVALVES(in2)阀门通径ValveSize压力等级PressureClass150300600900150011/2221/23468101214161