Control valve selection for pipeline

[MT47]

Hi,is there any one to help me for selection of control valve type.The control valve should be installed on 24 inch Crude pipeline.Maximum diffrential pressure for control valve is 3 bar .Is there any standard for the control valve selection? I am really thankful.

 

[zdas04]

A control valve in a 24" pipeline? What are you trying to control (flow, pressure, dP, etc.)?

In a line that size you usually can't tolerate much more than 2-3 psi/mile pressure drop so if you are putting a control valve on it then you'll need one with minimal dP when full open--in my experiance that calls for something like a Fisher V-Ball (if they even come in that size).

If you're looking for on/off control then a full-port actuated ball valve is the choice. For mainline block valves I always use trunion ball balves.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[MT47]

Dear David
thank you for your attention in this matter.you see The objective of the control of crude oil pipeline pump system is two folds:to keep the discharge below the maximum pressure for which the pipe is rated and to prevent the suction pressure from dropping below thw net positive suction head.the latter objective prevents cavitations of pump.Since we have two pressure to control,suction and discharge,and only one control valve on the suction,a selective control system is used.your response will be highly appriciate and we remain.
Best Regards

 

[MortenA]

It seems to me that what you have is an oversized pump?

Pressure and flow is connected. When you introduce a pressuredrop you restrict flow.

When you say that you want to " prevent the suction pressure from dropping below thw net positive suction head" then what you actually are trying to acomplish is to reduce the flow rate so that the pressuredrop upstream the piping does cause the NPSHa to drop below NPSHr. The reduced flow causes the pump to "crawl back up" your pump curve thus increasing the head. Now you have to ballance between pipeline design pressure and suffciently low flow to prevent cavitation.

It sound to me that a better appraoch would be to re-examine your pump. Perhaps the impeallars can be modified/replaced so that the nominal capacity of the pumps drops.

This will solve your NPSH problems and will also reduce the energy consumption of your pump! If I assume that the velocity in the pipeline is 2 m/s, you pipeline ID=0.58m, the density .9 and the overall efficiency .9 then this amouts to a saving of:

2*0.58^2*pi/4*3600*33*.9/367/.9=171kW (all in metrics)

Instead of installing a valve! Now you may have operating conditions that changes and thus makes this impractical/useless - but you should still consider it.