7 replies to this topic

[processengineer1998]

Dear Friends;

I am going to size control valve for minimum flow line of centrifugal pump.From pump vendor data I know minimum flow requirement(30% of normal flow). The question is about pressure upstream control valve for control valve sizing.should I use pump discharge pressure at normal flow or pressure correspond to 30% flow from pump curve?

 

p.s. i consider flow rate as NORMAL flow rate for control valve sizing.Does anybody advise to use this flow as maximum flow through control valve?

thanks in advance

Edited by processengineer1998, 01 September 2017 - 09:02 AM.

[fallah]

Dear Friends;

I am going to size control valve for minimum flow line of centrifugal pump.From pump vendor data I know minimum flow requirement(30% of normal flow). The question is about pressure upstream control valve for control valve sizing.should I use pump discharge pressure at normal flow or pressure correspond to 30% flow from pump curve?

 

p.s. i consider flow rate as NORMAL flow rate for control valve sizing.Does anybody advise to use this flow as maximum flow through control valve?

thanks in advance

 

Hi,

 

You should find the pressure corresponding to the minimum flow rate (specified by vendor) from the pump curve and apply as upstream pressure in CV sizing...

 

The minimum flow is to be considered as normal/maximum flow in CV sizing...

[processengineer1998]

Thanks a lot Mr.Fallah

[simadri]

Hi processengineer1998,

If you are in initial stage of design, you will not get pump curve.

In that case 30% of normal flow is not a good assumption for minimum flow line of centrifugal pump.

I had seen pumps with minimum flow requirement specified by vendor even more than 40% of rated capacity (not for small capacity pumps). hence, I use following method during engineering.

 

For minimum flow line sizing, I consider 40% of rated flow for minimum re-circulation line.

For minimum flow line control valve data sheet, I consider valve shut-off pressure = Pump shut-off pressure. As initially, pump curve will not be available, pump shut-off pressure is considered as max. suction pressure + 1.25* calculated pump differential pressure.

 

For control valve upstream pressure, in absence of pump curve, I consider it as max. suction pressure + 1.2* calculated pump differential pressure.

 

All these parameters shall be checked after receiving pump curve from vendor during detail engineering stage.

 

I hope comments on this method from other members.

[processengineer1998]

Thanks Mr.Simadri
We have vendor data for minimum flow=13m3/hr

Another basic question is about requirement of minimum flow if there is a shut down signal for pump at higher flowrate.
In our case we need pump for pipeline.pipeline turndown is 16m3/hr and below this flowrate a signal will trip our pump.in this case what is the reason for considering minimum flow line for minimum flow of 13m3/hr because our pump already were shut down due to signal activated at 16m3/hr.

[christopherchoa]

I hope comments on this method from other members.

 

In our company (Fluor), we use a flat curve (same dP as the rated flow) for the minimum flow case. It will still give a much higher head than the pump curve. Thus, more conservative for the minimum flow case of the control valve.

[ecas]

You must clarify with the pump vendor if the minimum flow of 13 m3/h is for continuous running or only intermittent running. Usually the pump vendor states a minimum flow for continuos running, but he is able to establish a lower minimum flow for running the pump only a limited time.

[breizh]

Hi ,

To add to this thread .

Hope this helps

 

Breizh

Edited by breizh, 22 September 2017 - 09:37 AM.