Axial Control Valve Sizing

[neroverdi41]

Hello

I need to make Axial Control Valve sizing for a line with a size of 16”.
Parameters:
P1=82-36 bar
P2=82-36 bar
Q=10000-100000 sm3/h
T=15 C

How can I size it? Also, why are two different pressure values given for inlet and outlet?
Can you help me urgently?

 

[georgeverghese]

Those values are probably the range of pressures for P1 and P2. This info you've presented is clearly not the sizing info. There should be 2 design cases for control valves:
a) Flow with P1/T1 and P2 /T2 which leads to max Cv
b) Min flow with P1 / T1 and P2 / T2 which leads to min operable Cv

If gas mol wt is not the same for the 2 cases, then this should also be declared.

My guess is that P1 at max Cv is 36barg, while P1 for min operable Cv is 82barg

There may be yet another case which leads to min downstream temp, which in turn may dictate what type of low temp materials of construction may be. Talk to the plant senior process/facilities engineer assigned to this project

 

[neroverdi41]

According to your estimation, what is the reason why the pressure at the inlet according to the maximum is lower than the inlet pressure according to the minimum? usually a range is always given. i always choose the highest of the inlet and the lowest of the outlet. is this correct?

You also said 36 bar inlet pressure at maximum Cv, then the outlet pressure should not be less than 36. but it is not available in the pressure range. so I did not understand what you said.

 

[LittleInch]

10: 1 turndown eh? pretty good so my guess is min flow is 82 bar in, 36 out at 10,000
Max flow is wide open and 100000 at 36 bar in and out for max actual volume flow.

 

[neroverdi41]

My friend, I don't quite understand what you mean, forgive me.

parameters: p1=86-36 bar, p2=86-36 bar, q=10.000-100.000 sm3/h t=15 C

according to you:
minimum flow= p1=86 bar, p2=36 bar, q=10.000 sm3/h
maximum flow= p1=36 bar, q=100.000 sm3/h
Is that correct?

what is the p2 value for maximum flow?

 

[LittleInch]

P2 for max flow is 36 bar.

Well maybe 1 bar differential.

Axial valves are pretty good when wide open.

 

[LittleInch]

Are you working for the valve supplier?

 

[georgeverghese]

Agreed, at max flow, P2 may be 36barg, while P1 may be 36+x barg, where x is the dp relevant for this max Cv case.

Note that in some services, for the max Cv case, it would be acceptable for calculated Cv to be < say 0.75x wide open Cv, while in other operating cases, it may be acceptable for calc Cv < 0.9x of wide open Cv. So this is also info the plant process engineer should disclose.

 

[neroverdi41]

Are you working for the valve supplier?

Yes, I am working. customers usually give inlet and outlet pressures as a certain range.

For example p1=75-35 bar p2=68-35 bar

what should I understand when they give such a range? how can I determine the maximum or minimum flow?

 

[LittleInch]

Yes, I am working. customers usually give inlet and outlet pressures as a certain range.

For example p1=75-35 bar p2=68-35 bar

what should I understand when they give such a range? how can I determine the maximum or minimum flow?

Then you need to ask them for their required min and max stream conditions both for flow and for min inlet pressure or you are in danger of oversizing the valve.

The more cases they give you the better as you can then see which is the governing case for your valve in terms of size, trim etc.

We can all guess what they mean, but only they know what they actually want the valve to do. Maybe the low pressure in and out only happens at their minimum flow? We don't know.