10 replies to this topic

[WilliamN]

Dear peers,

I have a 2” control valve on a river water make up line to a cooling tower basin. The control valve maintains the basin water level about 4 feet. The river water header pressure is 150 psig. The control valve makes very loud noise. I assume the noise is from valve cavitation. I contemplate that the noise is caused by too much pressure drop across the valve – almost 150 psi. I am thinking to install either an orifice or pressure reducing valve upstream of the control valve to share the pressure drop, for example, reduce the pressure from 150 psig to 50 psig by the orifice or pressure reducing valve, then pressure drop across the control valve will be 50 psi, not 150 psi.

 

I appreciate your comments if this idea helps to reduce the noise from the control valve.

[TS1979]

Yes. It seems that you have a control valve cavitation issue. Control valve cavitation depends on valve types and valve characteristics. There is a critical pressure drop (Single stage linear valves -15 bar, butterfly and ball valve - 5 bar). The dissolve gases will also affect the cavitation. If you have a cavitation problem, have you observed that in the winter time the cavitation is mitigated because of low river temperature?

 

Orifice plate will mitigate the cavitation problem.

[WilliamN]

TS, Thanks for your advice, I will try out the orifice option.

[WilliamN]

Dear peers,

My coworker recommends to install a pressure reducing valve upstream of the control valve, say the pressure is reduced from 150 psig to 100 psig . so the inlet pressure to the control valve will be 100 psig, rather than 150 psig. With this scheme, the pressure drop across the control valve is reduced. I appreciate any comments from peers if this design helps to mitigate the control valve cavitation issue.

 

Thanks.

[Ajay S. Satpute]

Hi,

 

As you know reducing upstream pressure (and pressure drop across control valve) would require control valve to open more. You need to make sure any changes you do, wouldn't make valve undersized.

 

 

I have assumed some values and result snapshot is attached herewith. Reduction in upstream pressure has caused valve open from 80% to 86% in this case.

 

Can you provide below details?

Valve characteristic curve (Linear/Eq.%),

Valve Cv,

Valve datasheet,

Max. flow

 

 

Regards.

 

Ajay S. Satpute

 

Attached Files

•  Snapshot.png   187.21KB   6 downloads

[PaoloPemi]

you can estimate the noise (for different installations)

with a method such as IEC 60534, this gives a good

indication of problems such as cavitation,

for given process conditions noise (and cavitation) depends mainly

from valve geometry (plug etc.) and you may be able

to find a suitable solution selecting a different valve,

if you do not have a software with IEC 60534

download Prode Valves or a similar one.

Edited by PaoloPemi, 08 April 2014 - 02:43 AM.

[mohit3040]

I agree with Mr. Ajay, as you are going to decrease the pressure drop across control valve, Cv value for max. flow case will increase.

 

Considering the Cv selection for the running control valve would have done based on 150 psi pressure drop for the max. flow case. Changing the pressure drop of the same control valve to 50 psi will almost increase the Cv to 1.7 times and hence increase the control valve opening requirement beyond 100% for the desired pressure drop i.e. 50 psi. Hence the same control valve seems to be inadequate as per the preliminary calculations. Further detailed analysis can be done.

[WilliamN]

Ajay,

I was able to locate some information from its name plate, etc.  The valve is a Masoneilan model with model # 35-35212. It has a linear characteristic with Cv=53. The max flow I am thinking  is ~100 gpm.

[Ajay S. Satpute]

Hi,

 

1. I used Cv = 53, Linear, Masoneilan (Camflex). Please refer attached snapshot for 2 cases (150 psig and 100 psig).

 

2. We can calculate the actual (and maximum) flow through the valve, if you can provide normal (and maximum) valve output (assuming the control valve bypass valve is holding). This information would help take a final call on whether to put orifice upstream of control valve.

 

3. Do you have any globe valve upstream of control valve, which you can try throttle and check any change in valve noise?

 

Regards.

 

Ajay S. Satpute

Attached Files

•  Cv_53.png   191.49KB   4 downloads

[xavio]

WilliamN,

 

Your control valve is cavitating for sure.

Putting RO or PRV upstream of the valve should help mitigate the problem, but the Cv requirement of the valve will change.

Original Cv could be too small to pass the required flow.

I suggest you find the valve vendor, ask them to perform the checking; replacing/modifying 2" valve shouldn't be too expensive.

 

A more direct solution would be using control valve with anticavitation trim.

 

Also be careful with determination of the pressure drop for RO/PRV, be sure you don't just shift the cavitation problem from the valve to the RO/PRV.

I think PRV is better if you expect the flow to be rather fluctuating.

 

xavio

[Zubair Exclaim]

valves in such servcie are designed for make up of level within a resonable time ... you just need to check that with modified inlet pressure the resulting flow that you get is good enough for filling the catch basin from low level to high level in resonable time ... i believe such systems are designe with enough margins and might be able to handle the modification you want.

 

vice versa determine the lowest possible flow you can live with and use a control valve sizing software from vendor and determine how much inlet pressure you can drop till you are within that flow limit.

Edited by Zubair Exclaim, 20 April 2014 - 05:43 AM.