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.

 

[neroverdi41]

my friend, the information has been updated.
Pipeline=16”
p1=82-36 bar
p2=66-36 bar
Q=10,000-100,000 sm3/h
T=15 C
Vmax=20 m/sec

the important thing for them is to ensure the necessary flow. when I calculate it in the sizing calculator on the fisher site, the Cv is too small. My understanding here is to make it the same size as the line diameter and allow as much flow as possible. What do you think?

 

[LittleInch]

You need to now for sure what the cases are. If its 100000 with inlet to outlet 82 to 66 bar or is it 36 bar?

Same size is rare in control valves. usually at least one or two sizes smaller.

I thought you worked for the vendor? Why are you using fishers calcualtor?

 

[neroverdi41]

I work for a supplier but why not use the fisher calculator? I don't understand. there are a lot of cv calculators on the internet and the fisher handbook has all the information on the internet about valve sizing.

 

[neroverdi41]

My maximum conditions are as follows:
pipeline=16”
p1=37 bar
p2=36 bar
Q=100000 sm3/h
T=15 C
Vmax=20 m/sec

I chose 2 lower ones as an estimate. The rated cv value of my 12” c600 axial valve is 1550. The Cv value I calculated is about 500. there is a big difference. Do you think this valve is suitable? or should I choose a smaller one? because if I choose this valve, I have it ready. I can change the cage design to lower the cv.

 

[SPDL310]

The information you have is not appropriate for sizing a valve as LittleInch has already stated. The customer normally fills out a standard valve spec sheet. It will pair a specific stream condition temp/flow/fluid properties with a given P1/P2 condition or maximum drop. This is determined by system and process requirements.

The valve you are proposing is oversized for the given scenario. You will need to assess the low and medium flow cases as well. With a max flow scenario only requiring about 1/3rd of the total valve capacity, you may not have enough turn down to maintain flow control in low flow scenarios. You will also have horrible rangeability as even an equal percentage characteristic curve will leave you operating in a fraction of the valves controllable range.

 

[neroverdi41]

As a result of my analysis, when I gave 37-36, ie dp=1 to the inlet and outlet, the flow rate of the valve was 10000. the desired flow range is 10000-100000 sm3/h. of course, I determined the minimum and maximum conditions by myself. would it be too big? can't I control it with a cage?

 

[SPDL310]

The 10,000 sm3/h figure seems more reasonable for a low flow scenario, and if that is the case your valve might not be over sized. The point that you seem to be missing is that what people have been trying to tell you is that this inquiry is not how valves are typically supplied. Your customer the system designer is the only one capable of knowing what function they wish for this vale to provide, and they are not clearly relaying this you. Not having a clear understanding of how the valve is expected to perform leads to you making assumptions for them which creates a liability for your employer if those assumptions prove inaccurate. If the same type of inquiry landed on the sales department of a major valve manufacturer they would either refuse to quote or drill down and demand a proper valve specification sheet be provided.

There will always be a minimum controllable Cv value for each valve. Typically the closer to that value you are operating the higher the likelihood of wearing out the trim. Valve designers typically warn that operating in the min or max 10-20 percent of the range is outside of the sweet spot that they prefer to operate in.

 

[LittleInch]

Well I estimate your actual velocity in the 16" pipe is only about 5m/sec at 37 bar at 100,000scm'hr.

That's pretty slow and for a control valve. Even at 12" that's only about 10m/sec.

So yes, your valve seems to be oversized.

Also a 10:1 turndown is quite high and with such a wide pressure range, it's going to be difficult to operate this valve at the fully open and nearly closed end of the

you still need better data.