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What is the operational phylosophy difference in pressure control valve and flow control vale and how it affects the sizing procedure?
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Control Valves
Started by vikramltv, Feb 03 2012 12:30 AM
2 replies to this topic
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#2
kkala
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Posted 03 February 2012 - 04:32 PM
A pressure control valve (PCV) opens or closes a bit more, when the sensed pressure changes.
A flow control valve (FCV) opens or closes a bit more, when the sensed flow changes.
Common examples: A PCV just upstream a flash vessel receiving condensate, keeps vessel operating pressure constant, irrespectively of condesate flow.
A FCV introducing atomizing steam into fuel oil burners regulates steam flow reset by fuel oil flow, so that mass ratio of steam / fuel be constant. To this effect fuel oil metering resets steam flow (other schemes can be also met).
Several examples of PCV or FCV can be seen on existing PIDs.
Sizing procedure is same for both valves, same data is written in their process data sheet. You have to specify upstream pressure P1 and downstream pressure P2 at max controllable flow as well as at min controllable flow (flows to be specified too). Besides normal flow and corresponding P1, P2 are usually specified. From this information required max Cv of the valve is specified, and a suitable valve from suppliers is selected to cover this max Cv. Sometimes only normal conditions are specified, especially in a hurry, but this has some risks, since rangeability (and relevant conditions) is not specified. Advice from others on it would be welcomed.
More explanations / expressions from others may promote understanding of the query.
A flow control valve (FCV) opens or closes a bit more, when the sensed flow changes.
Common examples: A PCV just upstream a flash vessel receiving condensate, keeps vessel operating pressure constant, irrespectively of condesate flow.
A FCV introducing atomizing steam into fuel oil burners regulates steam flow reset by fuel oil flow, so that mass ratio of steam / fuel be constant. To this effect fuel oil metering resets steam flow (other schemes can be also met).
Several examples of PCV or FCV can be seen on existing PIDs.
Sizing procedure is same for both valves, same data is written in their process data sheet. You have to specify upstream pressure P1 and downstream pressure P2 at max controllable flow as well as at min controllable flow (flows to be specified too). Besides normal flow and corresponding P1, P2 are usually specified. From this information required max Cv of the valve is specified, and a suitable valve from suppliers is selected to cover this max Cv. Sometimes only normal conditions are specified, especially in a hurry, but this has some risks, since rangeability (and relevant conditions) is not specified. Advice from others on it would be welcomed.
More explanations / expressions from others may promote understanding of the query.
Edited by kkala, 03 February 2012 - 04:43 PM.
