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2

# How To Convert Kvs-Value For Water To Kvs For Gas?

kvs

8 replies to this topic
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### #1 Falko

Falko

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Posted 12 January 2022 - 01:43 AM

Hello,

for an instrument I have given the Kvs-Value for water and I want to convert it to gas. Can someone help or explain the calculation?

Of course i  have the formulas for liquid and for gas calculation.

How do i convert it?

Thanks for the help

Falko

### #2 breizh

breizh

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Posted 12 January 2022 - 04:58 AM

Hi,

I'm not sure i understand the query . Do you mean you have a control valve for water and you want to use it for gas ?

https://www.engineer...nts-d_1931.html

Breizh

### #3 latexman

latexman

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Posted 12 January 2022 - 08:32 AM

You can transform Kvs into a dimensionless K value (or is it a C value in Europe?), then it can be used for all gasses and liquids alike.  Just use the correct equations for the situation - incompressible, compressible, choked, etc.  To transform Kvs just substiture the definition of Kvs into the Darch equation.  If this does not sound familiar, I recommend you seek and obtain Crane Technical Paper 410 as a reference.

### #4 Falko

Falko

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Posted 12 January 2022 - 09:22 AM

Hi,

I'm not sure i understand the query . Do you mean you have a control valve for water and you want to use it for gas ?

https://www.engineer...nts-d_1931.html

Breizh

Yes, it's a check valve and i have the Kvs for water and i need it for air, but i don't know how to convert it. The formulas for liquid and gas I know/have. Can i put the liquid Kvs on the left side of the gas equation and then e. g. calculate the volume flow? Kv=Vg/519 * root((rohGT1)/(delta p * p2)  I have a liquid Kvs and need a relation to a gas flow. Liquid Kvs is 42 m³/h for water, How much air can I put threw the valve?

Falko

### #5 latexman

latexman

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Posted 12 January 2022 - 10:33 AM

What is the numerical value of Kvs for water of the check valve?  What pipe diameter is the check valve?

Using symbology it is Kvs m3/hr at a pressure drop of 1 bar.

The Darcy equation for a valve is hL = K v2/2g.  Remember, K ≠ Kvs.

So calculate the velocity given Kvs m3/hr and the pipe ID.  Calculate the head loss that corresponds to 1 bar.  Calculate K.

Now use that K with the gas properties and the pertinent gas equation to get what you need.

### #6 Falko

Falko

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Posted 13 January 2022 - 07:07 AM

I have the check valve DN50 with a Kvs of 42 m³/h for water. I want to use it for air. How much air can go through it? On one side is the atmosphere, on the other side is maximum -100 mbar.

How much air can go through it? Hoch much air will go through under this conditions? How much air at opening 100%?

Falko

### #7 breizh

breizh

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Posted 13 January 2022 - 07:53 AM

Hi Falko ,

It's difficult to understand your query .  A check valve is not an instrument , it's an equipment .Like any other fittings, it follows the Darcy Weisbach equation (head loss versus [ velocity or Flow rate } ^2 .

BTW which type of check valve are you talking about? what is the brand?

https://www.rusa-or....eck Valves1.pdf

In operation the check valve must be fully open  this means you have to find the relevant catalogue for this piece of equipment ( Internet is another option) and check its capacity for air .

My view

Breizh

### #8 latexman

latexman

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Posted 13 January 2022 - 08:13 AM

Is the check valve spring loaded?  If so, what is it's cracking pressure (CP)?  If CP > 100 mbar, then flow is zero.  Is the check valve screwed, flanged or welded connections?

I can help get you part of the way to the answer with what we know already:

42 m3/h = 700 LPM.

In DN50 (2" Sch. 40 = 2.067" ID), v = 17.7 ft/sec (5.4 m/sec)

For a pressure drop of 1 bar (14.5 psi), K = 6.9 (dimensionless).  See attached .pdf.

If the check valve is not spring loaded, it has a relatively large resistance compared to 2" swing check.  What type check valve is it?  A lift check?

You see, we are guessing, because you have failed to give complete, detailed information.

### #9 breizh

breizh

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Posted 20 January 2022 - 09:56 PM

Hi,

Consider this resource :

https://neutrium.net...en-cv-kv-and-k/

Breizh