8 replies to this topic

[OO22KK]

Pls i need the Equation for an Equal percentage Valve characteristics.

[gvdlans]

Pls i need the Equation for an Equal percentage Valve characteristics.

Try this site: www.google.com

[ankur2061]

Pls i need the Equation for an Equal percentage Valve characteristics.

Hi,

What do you mean by equation for equal percentage valve characteritics?

Equations for control valve correlate flow rate (mass or volume) to valve coefficient, fluid specific gravity, delta P across the control valve. And the equations for gas service and liquid service differ. I have never come across a equation for equal percentage valve characteristics.

Equal percentage implies the flow behaviour of the valve in terms of opening and closing of the valve. Here is what GPSA Data book has to say about control valves with equal percentage characteristics:

Equal-Percentage Flow Characteristic:
In this flow characteristic, equal increments of valve travel (opening) produce equal percentage changes in the existing flow. The change in flow rate is always proportional to the flow rate just before the change in position is made for a valve plug, disc or ball position. When the valve plug, disc or ball is near its seat & the flow is small, the change in flow rate will be small; with a large flow, the change in flow rate will be large.

Applications of Equal-Percentage Flow Characteristic Control Valves:
These are generally used for pressure control applications. They are also used where a large percentage of the total system pressure drop is normally absorbed by the system itself, with only a relatively small percentage by the control valve. These are also recommended for applications where highly varying pressure conditions can be expected.

You need to clarify further about the equation you are expecting.

Regards,
Ankur.

[sheiko]

Pls i need the Equation for an Equal percentage Valve characteristics.

The valve opening L (in percentage) equation for an equal-percentage control valve is:

L = 100*[1+ln(CV/CVmax)/lnR], with:

CV = flow coefficient at a particular condition (flow rate, fluid specific gravity, delta P across the control valve)

CVmax = flow coefficient at 100% opening (or L=100)

R = rangeability (ratio of max to min flow - usually in the 20 to 50 range for globe valves)

Is that what you need?

[breizh]

Pls i need the Equation for an Equal percentage Valve characteristics.

Hi ,
have a look at this excellent tutorial .
http://www.spiraxsar...stics.asp#head5

regards
Breizh

[OO22KK]

Thanks alot sheiko....this is what I need.

Pls can you provide the reference material (website or Book title) with the derivation of this formular?

[OO22KK]

thanks Breizh..

[OO22KK]

Hi Ankur,

I need an equation relating the valve travel (or lift) to CV (or flowrate) for an equal percetage valve.

Regards,

[sheiko]

Thanks alot sheiko....this is what I need.

Pls can you provide the reference material (website or Book title) with the derivation of this formular?

From an article issued in Hydrocarbon Processing magazine in 2007 and untitled: "Visualize pump and control valve interaction easily".