阀门流量计算方法

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15o C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15o C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 60o F water with a pressure drop (dp) of 1 PSI across the valve. A Cv of 350 means a valve will pass 350 gpm of 60o F water with a dp of 1 PSI.

公式1

FORMULA 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：PSI

dp = pressure drop in PSI

F = 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2

FORMULA 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：PSI

dp = pressure drop in PSI

Sg = 比重

Sg = specific gravity

Q = 流速，单位：加伦/分钟

Q = flow rate 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 flashing.

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

EXAMPLE

1.通过DN350, 压力等级Class 900的压力密封闸阀，水温400o F，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 400o F water, 1500 PSIG, and 5,000,000 lbs/hr flow rate?

解：采用公式1

Solution: Use formula 1.

F = 5,000,000

= 0.137 (从水温为400o F的表中得到)

= 0.137 (from chart for water at 400o F)

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 14"x12"x14" Class 900 Venturi pressure seal gate valve with the same conditions as example 1.

解：采用公式1

Solution: Use formula 1.

Cv = 6285 (来自本页)

Cv = 6285 (from page 26)

3.温度900o F, 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

900o F, 1200 PSI steam service at a flow rate of 500,000 lbs/hr?

解：采用公式1

Solution: Use formula 1.

F = 500,000

= 0.785 (来自900o F, 1200 PSIG蒸汽表)

= 0.785 (from chart for steam at 900o F, 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。