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Level Control Valve Sizing

control valve lcv sizing calculation valve

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#1 rjd452


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Posted 01 October 2022 - 05:23 PM

I am trying to size a LCV from a separator, The separator pressure is 75 psig and the downstream of LCV goes to a vessel where pressure is maintained by blanketing at 5 psig. 

What DP should be considered for the control valve? should it be 75 - 5 = 70 psig or 

for the downstream of LCV should we consider pr. drop across piping also??


Since LCV only maintain level, is the pressure downstream of LCV defined by system pressures?

If the pressure downstream of LCV suddenly rises to more than 5 psig and differential pressure acorss lcv reduces, what will happen in that case? will flow reduce and ultimately level will not be maintain?

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#2 breizh


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Posted 02 October 2022 - 12:00 AM


The pressure at the outlet of the valve is the pressure in the receiver (drain tank) +the head loss of the pipe downstream of the valve.

It's a back calculation where you apply Bernoulli theorem.


#3 Pilesar


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Posted 02 October 2022 - 02:20 PM

Repeating Breizh's answer in a different way... With LCV closed, what is the pressure downstream of the LCV? With the LCV passing maximum desired flow, what is the pressure downstream of the LCV? Both of these pressures are calculable from the Bernoulli equation. The results give you the range of flow rates with their downstream pressures. Now calculate the pressure upstream of the LCV for the different flow rates. You will find there is a gap between the upstream pressure and the downstream pressure at the different flow rates. The control valve is what fills that gap! Design the valve so that it can handle the range of flows you already calculated with the pressure drops available. If there is not enough pressure drop available for the valve, you may need to increase line sizes.

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