dear all,

i am trying to calculate control valve sizing. can anybody guide me for calculating Cv using various formulas.

 

Dear Sir,

We are control valve manufacturer in Taiwan! I could send you one formula attachment for calculating water CV under the planned circumstances,and you could check the CV value result. By comparing the CV value offered by each brand for chooosing control valve's size of each different brand.

Please contact me since I could not attached the calculation document in this coulumn.

Best Regards,
Miguel Chen/Elite Line

 

Its a huge question. there are large books on that issue. try finding any 'conrol valve handbook' that can be very helpful. besides there are too many parameters to consider

 

Tushar,

I would ask you to go to www.google.com and type Fisher Control Valve Handbook" and download the book. this book gives you the required information about Control Valves - selection, sizing etc.

I found this book very useful. whatever you discuss in the forum, it is less. Go for that book - it is a free download.

My suggestion: Get the previous datasheets of your plant related to Control valves and try to use the formulae given in the book and check the calculated values. Thereby, you get a lot of practice.

Good Luck!

 

It depends for which application control valve you want to size as for liquid,gas etc.they have different sizing factor.U can search on net...there is a thumb rule u can follow it for liquid application

Step1.Observer the dia of the pipe for which control valve is required.
e.g 300mm

Step-2: Take the half of the value of pipe size
e.g 150mm

step-3 pick the control valve one size higher than the available in the market
e.g 200mm

 

Dear Miguel,
Would you please give your email address?

regards,
Vahid

 

We host the Fourth Edition (current one)of the "Little Black Book" also known as the Fisher Control Valve Handbook at
http://www.controlglobal.com/whitepapers/2006/059.html.

It is a reference no engineer should be without.

In addition, there are other white papers on control valves, from Metso, Emerson, Honeywell, and others.

But the real star of the show is the three part series by Bela Liptak on sizing control valves:

Part One: http://www.controlglobal.com/articles/2006/132.html

Part Two: http://www.controlglobal.com/articles/2006/167.html

Part Three: http://www.controlglobal.com/articles/2006/215.html

As part of this series, Bela created what I believe is the only modern impartial guide to control valve selection:
http://www.controlglobal.com/Media/MediaManager/article_132_controlvalves.pdf

I hope this helps!

Walt Boyes
Editor in Chief
Control and Controlglobal.com
www.controlglobal.com
Mailto:wboyes [at] putman.net
Read my blog SoundOFF!! At www.controlglobal.com/soundoff

 

dear sir,

thank you for your reply. my mail id is tusharinst [at] hotmail.com.

tushar

 

Dear Miguel Chen,

Could you please e-mail to me your formula also. It could be useful for me.

Best Regards,
Faizul
faizulism4007 [at] yahoo.com

 

Dear Sir,

We are EPCC Agency for Pneumatic conveying systems for solid handeling based at Baroda, India.

We required approx 200 different valve for our project.

We float the inquiry for valves. we got some quote with valve sizing data. In that How to check the rated CV for particular valves.

Can you help in this regards.

Thanking You.

Regards

Vivek Shah
Project Engineer
For,
Zeppelin Systems India Pvt. Limited
Level 4, ADM Building,
Alembic Campus, Alembic Road,
Vadodara-390003
India.

 

Hi there,

It is not all that complicated once you have the right formulas to work with. Here are some examples.

LOOK AT THE NOTES AT THE BOTTOM FIRST BEFORE YOU READ ANY FURTHER!!!!

Calculate the cv of a LIQUID ONLY control valve for a given flow, dp and sg
<pre>
Cv = 11.7 q (SG / dp)1/2

where
q = Expected flow rate (m3/h)
Sg = Specific gravity of the liquid (1 for water in this example)
dp = Pressure drop across the valve at expected flow rate (kPa)

Example 1.
So if q = 5m3/h
Sg for water = 1
Dp over valve during 5m3/h flow = 10kpa

Do manual calculation:

Cv = 11.7 q (SG / dp)1/2

1) 11,7 x 5 = 58,5
2) 1/10 = 0,1
3) ½ = 1/2 = 0.5
4) 0,1 to the power of 0,5 = 0.31622776
5) So 0.31622776 x 58,5 = 18,49

So a valve with a cv of 18,5 is needed to do a flow of water(sg=1) at 5m3/h and a dp over the valve of 10kpa

Look at manufacturer valve manual for available valves and
select a valve with a next bigger Cv.

----------------------------------------

Example 2.
So if q = 30m3/h
Sg for liquid = 0,97
Dp over valve during 30m3/h flow = 110kpa

Do manual calculation:

Cv = 11.7 q (SG / dp)1/2

1) 11,7 x 30 = 351
2) 0,97/110 = 0,008818
3) ½ = 1/2 = 0.5
4) 0,008818 to the power of 0,5 = 0.0939042
5) So 0.0939042 x 351 = 32,96

So a valve with a cv of 32,96 is needed to do a flow of
liquid (sg=0,97) at 30m3/h and a dp over the valve of 110kpa

Look at manufacturer valve manual for available valves and
select a valve with a next bigger Cv

---------------------------------------

Example 3.
So if q will be 64m3/h
Sg for liquid is 0,87
Dp over valve during 64m3/h flow is 210kpa

Do manual calculation:

Cv = 11.7 q (SG / dp)1/2

1) 11,7 x 64 = 748,8
2) 0,87/210 = 0,00414285
3) ½ = 1/2 = 0.5
4) 0,00414285 to the power of 0,5 = 0.06436497
5) So 0.06436497 x 748,8 = 48,196


So a valve with a cv of 48,196 is needed to do a flow of liquid (sg=0,87) at 64m3/h and a dp over the valve of 210kpa

Look at manufacturer valve manual for available valves and
select a valve with a next bigger Cv

------------------------------------------

To do the power off calculation on your windows calculator:
Example:
5 to the power of 4

press 5 then x^y then 4 then =

--------------------------------------------

Control Valve selection Flow Coefficient - Cv - for Air and other Gases

For critical pressure drop the outlet pressure - po - from the control valve is less than 53% of the inlet pressure - pi. The flow coefficient can be expressed as:

Cv = q [SG (T + 460)]1/2/ 660 pi
where
q = free gas per hour, standard cubic feet per hour (Cu.ft/h)
SG = Specific gravity of the gas relative to air at 14.7
psia and 60oF
T = flowing air or gas temperature (oF)
pi = inlet gas absolute pressure (psia)

Example:
5000 = Gas flow (Cu. ft./h) (f.a.d)
100 = Inlet Gas Absolute Pressure (psia)
1 = Specific gravity of the gas
60 = Gas Temperature (oF

Do manual calculation:

Cv = q [SG (T + 460)]1/2/ 660 pi

1) 60 + 460 = 520
2) 520 x 1 = 520
3) ½ = 1/2 = 0.5
4) 520 to the power of 0,5 = 22,8035
5) 22,8035 x 5000 = 114017,5425
6) 660 x 100 = 66000
7) 114017,5425 / 66000 = 1,727

So a valve with a cv of 1,73 is needed to do a air flow (sg=1) at 5000Cu.f/h, at a air flow temp of 60F and a inlet gas absolute press of 100PSIA

Look at manufacturer valve manual for available valves and select a valve with a next bigger Cv

-----------------------------------------------

For non critical pressure drop the outlet pressure - po - from the control valve is greater than 53% of the inlet pressure - pi. The flow coefficient can be expressed as:

Cv = q [SG(T + 460)]1/2/ [1360(dp*po)1/2]
where
dp = (pi - po)
po = outlet gas absolute pressure (psia)

Example:
6000 = Gas flow (Cu. ft./h) (f.a.d)
140 = Inlet Gas Pressure (psia
110 = Outlet Gas Pressure (psia
1 = Specific gravity of the gas
60 = Gas Temperature (oF)

Do manual calculation:

Cv = q [SG(T + 460)]1/2/ [1360(dp*po)1/2]

1) 60 + 460 = 520
2) 520 x 1 = 520
3) ½ = 1/2 = 0.5
4) 520 to the power of 0,5 = 22,8035
5) 22,8035 x 6000 = 136821,051
6) 140 - 110 = 30
7) 30 x 110 = 3300
8) ½ = 1/2 = 0.5
9) 3300 to the power of 0,5 = 57,445
10) 57,445 x 1360 = 78126,05199
11) 136821,051 / 78126,05199 = 1,75

So a valve with a cv of 1,75 is needed to do a air flow (sg=1) at 6000Cu.f/h, at a air flow temp of 60F and a DP of 30PSIA absolute press

Look at manufacturer valve manual for available valves and
select a valve with a next bigger Cv

--------------------------------------------------

To do the power off calculation on your windows calculator:
Example:
5 to the power of 4 ------- press 5 then x^y then 4 then =
</pre>
--------------------------------------------------

NOTE!!!

Please note the "1/2" in the formulas is not as it seems, it is suppose to be a small "1/2" on the top right hand corner of the bracket, in other words a "to the power of 1/2" and
not " bracket times 1/2 as it is displayed"
Cannot seem to get it displayed like that on this page - sorry if it is confusing but look at he calculation to see where the "power of" is used and you will understand what I mean.

Good Luck

 

hey there,

could you send me the formula or anything about the control valve sizing info. to me as well?? thank you very much. my email address is lscnlemon [at] yahoo.com.cn

 

hi gents.

is there any valve sizing calculation to share.

 

Control Valve Size determination... see:

http://control.com/thread/1275377381

Regards, Phil Corso

 

Dear sir

I have been working on the power calculation in control valves but couldn't come to a specific conclusion. could you help me with the
formula used in power calculation and power factor details for (control valves)

id [email protected]
[email protected]

 

Mary... if your question was addressed to me, then there is some confusion.

Power and power factor calculations are not related to valve sizing. However, perhaps your question is related to motor sizing?

Regards, Phil Corso

 

>We are control valve manufacturer in Taiwan! I could send you one formula attachment for calculating water CV under the planned circumstances,and you could check the CV value result. By comparing the CV value offered by each brand for chooosing control valve's size of each different brand.
>
>Please contact me since I could not attached the calculation document in this column.

Send that to me sir, i am working as Trainee in Instrumentation field
[email protected]

 

Dear Miguel Chen/Elite Line,

I am looking for control valve (Taiwan). pls send me catalogue of you. My email: [email protected]
Best regards

 

our sizing data sheet produces a factor called power and power factor and maximum power based on the fluid medium the power formulae varies and based on the size the maximum power varies to some constant inbuilt value and the power factor is the ratio of the power calculated to the max power

just wanted to know what this power is all about is it related to

 

Dear Sir,

You can go to SAMSON.DE there is a valve sizing program you can download free and also in the information spec sheet No: t80001en (can also see it searching in google)you can see the formulas there.

Hope this is useful for you.