阀门流量计算方法介绍(doc 18页)

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.

a.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.

b.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

900

o 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。

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.

水和蒸汽的备选特性

Selected Properties of Water and Steam

水的(下游)

For Water (Downstream)

所有压力等级

All Pressures

温度(o F)

Temperature (o F)

100 200 300 400 500 600 0.127 0.129 0.132 0.137 0.143 0.154

蒸汽的(下游)

For Steam (Downstream)

压力PSIG Pressure PSIG

温度(o F)

Temperature (o F)

Sat 500 600 700 800 900 1000 1100

100 200 1.97

1.46

2.20

1.61

2.32

1.68

2.44

1.77

2.54

1.85

2.64

1.95

2.74

2.00

2.84

2.07