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# Capacity Of Control Valve When 100%opening

control valve

2 replies to this topic
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### #1 Takechi

Takechi

Veteran Member

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• 38 posts

Posted 13 August 2017 - 09:27 AM

Dear all

I would like to consult you about the control valve.

My control valve was design at below condition

Flow rate(m3/h)                        :  max. = 79.1, Nor. = 79.1, Min. 37.2

Inlet press.(kg/cm2g)               :   max. = 61.9, Nor. = 61.9, Min. -

Diff press.(kg/cm2)                   :   max. = 2.8, Nor. = 2.8, Min. -

Temp(degC)                             :   max. = 320, Nor. = 312, Min. 300

Cal. CV                                    :   max. = 45.74, Nor. = 45.74, Min. 21.50

Rated CV                                 :   165

How can I calculate when control valve open 100%op?

Best regards,

Salapao.

### #2 Saml

Saml

Gold Member

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• 290 posts

Posted 13 August 2017 - 07:35 PM

You have to solve the flow for a Cv of 165.

### #3 vjmromero

vjmromero

Brand New Member

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Posted 14 August 2017 - 09:12 PM

First, you need to establish how much is the available head i.e. pressure at pump discharge (or source pressure). Say pressure is 80 kg/cm2,

we can assume that flow is turbulent, and only hydraulic circuit has dP only due to PIPING and control valve.

Then, dP of line is proportional to Q^1.9.

Total Total P = Destination P + dP line + dPvalve ;  dPline = TotalP-Destination P - dPvalve

(80-59.1-dPvalve) / (80-59.1-2.8) = (Qmax/79.1)^1.9    --- eqn 1.

For control valves, Q is proportional to Cv*sqrt(dPvalve)

Then,

Qmax/79.1 = 165/45.74 sqrt (dPvalve/2.8)

so, Qmax=285.341 (dPvalve/2.8)^0.5   -- eqn 2.

Solving simultaneously, Qmax=84.75 m3/h... (assumption source P at pump discharge = 80 kg/cm2; same condition applies i.e. liquid level or static head at source and destination are the same for all cases)