閥門流量計(jì)算方法如何使用流量系數(shù)How to use Cv　　閥門流量系數(shù)(Cv)是表示閥門通過流體能力的數(shù)值Cv越大，在給定壓降下閥門能夠通過的流體就越多Cv值1表示當(dāng)通過壓降為1 PSI時(shí)，閥門每分鐘流過1加侖15oC的水Cv值350表示當(dāng)通過壓降為1 PSI時(shí)，閥門每分鐘流過350加侖15oC的水　　Valve coefficient (Cv) is a number which represents a valve's ability to pass flow. The bigger the Cv, the more flow a valve can pass with a given 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/小時(shí)(蒸汽或水)　　FLOW RATE LBS/HR (Steam or Water)　　在此：Where:dp=壓降，單位：PSIdp=pressure drop in PSIF=流速，單位：磅/小時(shí)F=flow rate in lbs./hr.=比容積的平方根，單位：立方英尺/磅(閥門下游)=square root of a specific volume in ft3/lb.(downstream of valve)公式2FORMULA 2　　流速：加倫/分鐘(水或其它液體)　　FLOW RATE GPM (Water or other liquids)　　在此：Where:dp=壓降，單位：PSIdp=pressure drop in PSISg=比重Sg=specific gravityQ=流速，單位：加倫/分鐘Q=flow rate in GPM局限性LIMITATIONS　　上列公式在下列條件下無效：　　Above formulas are not valid under the following conditions:a. 對(duì)于可壓縮性流體，如果壓降超過進(jìn)口壓力的一半。

For compressible fluids, where pressure drop exceeds half the inlet pressure. b. 對(duì)于不可壓縮性流體，如果壓降產(chǎn)生空穴或閃蒸For non-compressible fluids, where pressure drop causes cavitation or flashing. c. 對(duì)于雙相流體，如蒸汽-水混合流體For dual-phase flow such as steam-water mixtures. 例子EXAMPLE1. 通過DN350, 壓力等級(jí)Class 900的壓力密封閘閥，水溫400oF，壓力為1500 PSIG，流速為5,000,000磅/小時(shí)的壓降是多少？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：采用公式1Solution: Use formula 1. F=5,000,000=0.137 (從水溫為400oF的表中得到)=0.137 (from chart for water at 400oF)Cv=9150 (來自本頁(yè))Cv=9150 (from page 26)2. DN350 x DN300 x DN350，壓力等級(jí)Class 900縮喉管壓力密封閘閥，其它條件與例1相同，求壓降。

What is the pressure drop through a 14"x12"x14" Class 900 Venturi pressure seal gate valve with the same conditions as example 1.解：采用公式1Solution: Use formula 1.Cv = 6285 (來自本頁(yè))Cv = 6285 (from page 26)3. 溫度900oF, 壓力1200 PSI，流速500,000磅/小時(shí)的蒸汽應(yīng)用中壓降小于5 PSI的壓力等級(jí)Class 2500閘閥的最小通徑是多少？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 flow rate of 500,000 lbs/hr?解：采用公式1Solution: Use formula 1. F=500,000=0.785 (來自900oF, 1200 PSIG蒸汽表)=0.785 (from chart for steam at 900oF, 1200 PSIG)== 2.24?　　最接近的、較大的Cv是DN250壓力等級(jí)Class 2500閘閥，其Cv是3130。

這里是壓降小于5 PSIG的最小的閥門　　The closest higher Cv is a 10" Class 2500 gate with a Cv of 3130. This is the smallest valve with a pressure drop less than 5 PSIG.水和蒸汽的備選特性Selected Properties of Water and Steam水的(下游)For Water (Downstream)所有壓力等級(jí)AllPressures溫度(oF)Temperature (oF)1002003004005006000.1270.1290.1320.1370.1430.154?蒸汽的(下游)For Steam (Downstream)壓力PSIG PressurePSIG溫度(oF)Temperature (oF)Sat5006007008009001000110010020030040050060070080090010001100120013001400160018002000250030004000500060001.971.461.211.060.9500.8650.8010.7470.7010.6620.6280.5980.5700.5452.201.611.301.110.9790.8952.321.681.381.191.060.9600.8800.8150.7590.7100.6700.6290.5900.5592.441.771.461.261.121.020.9410.8750.8210.7730.7320.6950.6620.6330.580.540.500.410.310.170.160.162.541.851.521.321.181.080.9940.9260.8700.8160.7810.7450.7100.6830.630.590.550.480.420.320.240.192.641.951.601.381.231.131.040.9720.9140.8650.8230.7850.7520.7230.670.630.590.520.460.380.320.282.742.001.651.431.281.171.081.010.9550.9170.8720.8130.7890.7520.700.660.620.550.490.420.360.322.842.071.711.471.331.221.121.050.990.940.900.860.830.790.740.690.650.580.520.440.390.35閥座端口流速計(jì)算Calculating Seat Port Velocity　　下列公式可以用來計(jì)算任何閥門的閥座流速：　　The following formulas can be used to calculate seat portvelocity in any valve:流量(磅/小時(shí)): 流速: (英尺/秒)= F()225AFlow (lbs/hr): vel: (fps) = F()225A流量(加侖/分鐘): 流速: (英尺/秒)= 0.32QAFlow (GPM): vel: (fps) = 0.32QA?在此：Where:F=流量(磅/小時(shí))F=flow (lbs/hr)=比容積的平方根=square root of specific volumeA=閥座端口面積 (英寸2)A=seat port area (in2)Q=流量 (加侖/分鐘)Q=flow (gpm)例：　　DN300型號(hào)58809 (壓力等級(jí)Class 900)止回閥，流體介質(zhì)為溫度500 oF，壓力200 PSIG的蒸汽，流速為90,000磅/小時(shí)，求閥座端口的流速？ 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：　　從蒸汽表得為1.61，從閥座端口面積表A得閥座端口面積為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。