阀门流量计算

阀门流量计算方法

发表于： 2010-1-29 9:39:55

如何使用流量系数

2. DN350 x DN300 x DN350，压力等级Class 900缩喉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

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

)

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 ft 3/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)

= 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

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)

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 port velocity in any valve:

2

F() 流量(磅/小时): 流速:

(英尺/秒)= 25A

阀座端口面积“A ”(英寸2) 适用于螺栓阀帽阀门

SEAT PORT AREA "A" FOR BOLTED

BONNET VALVES (in2)

2

F() Flow (lbs/hr): vel:

(fps) = 25A

流量(加仑/分钟): 流速: 0.32Q

(英尺/秒)= A

Flow (GPM): vel: (fps) = 0.32Q

A

在此： Where:

F = 流量(磅/小时) F = flow (lbs/hr)

= 比容积的平方根

= square root of specific volume

A = 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 o F ，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 o F and 200 PSIG?

阀座端口面积(英寸2)

适用于压力密封闸阀，截止阀，提升式阀瓣止回阀 SEAT PORT AREA FOR PRESSURE SEAL GATE, GLOBE, TILT DISC CHECK VALVES (in2)

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.

90,000 流速: (

英

F() 2

(1.61)2 = 118.8 英尺/秒)= =

25A

尺/秒

25 (78.5) F() 2

90,000 Vel (fps) = =

(1.61)2 = 118.8 fps

25A

25 (78.5)

例：

DN300型号180 (压力等级150) 旋启式止回阀，流体介质为温度500o F ，压力200 PSIG的蒸汽，流速为90,000磅/小时，求阀座端口流速？ Example:

What is the seat port velocity in a 12" Figure 180 (Class 150) Swing Check Valve with a flow rate of 90,000 lbs/hr of steam at 500o F and 200 PSIG?

阀座端口面积(英寸2) 适用于压力密封Y 形截止阀

SEAT PORT AREA FOR PRESSURE SEAL Y-GLOBE

VALVES (in2)

解：

查表得为1.61，A 为 113.1英寸3. Answer:

From the tables is 1.61 and A is 113.1 3in .

2

F() 流速: (英

=

尺/秒)= 25A

90,000 (1.61)2 25 (113.1) 90,000 (1.61)2 25 (113.1)

= 82.5英尺/秒

F() 2

Vel (fps) = =

25A

= 82.5 fps

局限性 LIMITATIONS

流速公式在下列条件下无效：

Velocity 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.

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：

When determining sizing for check valves, the optimum operating velocities should fall within these ranges:

BB 旋启式止回阀：55 至115或135至240

BB 截止止回阀：40 至120 PS 提升式阀瓣止回阀：55至200 PSY 形止回阀：148 至200 BB Swing Check Valves - 55 to 115 or 135

to 240

BB Stop Check Valves - 40 to 120

PS Tilt Disc Check Valves - 55 to 200 PS Stop Check Valves - 40 to 180 PS Y- Stop Check Valves - 148 to 200

螺栓阀帽闸阀全开状态下的流量系数Cv

螺栓阀盖旋启式止回阀全开状态下的流量系数Cv

Bolted Bonnet

Gate Valves FULL OPEN Cv

Bolted Cap

Swing Check Valves FULL OPEN Cv

图1 螺栓阀帽截

止阀 Figure 1 Bolted Bonnet Globe Valves (1)当开启度

小于 10%时，不建

议 用于节流应用。 (1) not recommended

for throttling at less than 10% Open.

螺栓阀帽截止阀全开状态下的流量系数Cv

Bolted Bonnet

Globe Valves FULL OPEN Cv

压力密封闸阀全开状态下的流量系数Cv

Pressure Seal

Gate Valves FULL OPEN Cv

压力密封缩喉管闸阀全开状态下的流量系数Cv

Pressure Seal

Venturi Gate Valves FULL OPEN Cv

压力密封提升式阀瓣止回阀全开状态下的流量系数Cv

Pressure Seal

Tilting Disc Check Valves FULL OPEN Cv

Characteristic Flow Curves for Globe Stop, Stop-Check, Lift-Check Valves

小于全开状态的估计流量系数Cv

Estimating Cv For Less Than Fully Open Valves

图2

球形止回阀，截止止回阀和提升式止回阀

Figure 2

Globe Stop, Stop-Check and

Lift-Check Valves 压力密封T 形球形止回阀，截止止回阀和提升式止

回阀

阀全开状态下的流量系数Cv Pressure Seal T-Globe Stop,

Stop-Check and Lift-Check Valves FULL OPEN Cv

图3

Y 形球形止回阀，截止止回阀和提升式止回阀

Figure 3

Y-Globe Stop, Stop-Check and

Lift-Check Valves 压力密封缩喉管球形止回阀，截止止回阀和提升式

止回阀

阀全开状态下的流量系数Cv

Pressure Seal Venturi Globe Stop,

Stop-Check and Lift-Check Valves FULL OPEN Cv

压力密封Y 球形止回阀，截止止回阀和提升式止回

阀

阀全开状态下的流量系数Cv Pressure Seal Y-Globe Stop,

Stop-Check and Lift-Check Valves FULL OPEN Cv压力密封缩喉管Y 球形止回阀，截止止回阀和提升

式止回阀

阀全开状态下的流量系数Cv

Pressure Seal Venturi Y-Globe Stop,

表中所列流量系数仅适用于全开状态下的阀门。不是全开状态的流量系数可以采用适用于提升式阀瓣止回阀和截止阀的流量特性曲线进行估算。不建议将闸阀用在节流应用中。

The flow coefficient (Cv) listed in the tables apply to fully open valves only. Flow coefficients at other than fully open may be approximated by use of the characteristic flow curves for tilting disc check and globe valves. Gate valves are not recommended for throttling service. 例：

解：

从上列流量系数表中得到，DN300，压力等级Class 900截止阀在全开状态下的Cv 是1820。 SOLUTION:

From the flow coefficient table above, the fully open Cv for a 12 inch, Class 900 globe valve is 1820.

查询图2，全开状态的1/4时阀门的比率是52%. Consulting Figure 2, the percent of fully open Cv at 1/4 valve open is 52%. 因此计算1/4全开的流量系数Cv 为： 0.52 x 1820 = 946.

The Cv at 1/4 open is then computed as:

0.52 x 1820 = 946.

DN300，压力等级Class 900的美国太平洋压力密封截止阀在开气度为1/4时的流量系数是多少？ EXAMPLE: What is the Cv of a 12 inch Class 900 Pacific pressure seal globe valve 1/4 open?