Can you control centrifugal pump flow with a flow meter? 1

[TXLSUCHE]

I have seen many threads concerning the use of control valves on the discharge of centrifugal pumps or VFD's to control flow, but none of them fit my particular case. I am designing pumps that will send oil into a pipeline which could vary substantially in pressure. Several articles that I have read say that the down side to using a pressure control valve on the discharge is that you are only controlling on pressure and the pump could dead head if operating in the "flat" portion of the curve. Not to mention, I don't want to trust the operators with being able to adjust the pressure setting without having an understanding of the pump curve. The use of VFD's aren't pratical in my case because operators may not be present to adjust the pump speed and we do not want the pumps to constantly shut down using pressure safety devices when the pipeline pressure fluctuates. Have any of you ever used a flow meter on the discharge in conjuction with a control valve to control the pump? I can't see any reason why this wouldn't work. We expect the flowrate upstream of the pumps to be fairly constant and if it isn't, there are bigger problems and the pumps would be shut down anyway.

Thanks in advance for your help.

 

[TD2K]

I have to be missing something here. Lots of pumps are controlled using a flow meter to adjust a control valve on the pump discharge to maintain the desired flow.

However, if the pipeline is going to vary 'substantially' in pressure, I'd take another look at VFDs since a fixed speed pump/control valve is going to have to be sized for the maximum pipeline pressure/flow combination which means you are wasting pumping energy across the control valve the rest of the time.

Why can't you use a flow meter to adjust the VFD or whatever parameter you want to control the VFD with?

 

[Bjegovic]

'The use of VFD's aren't pratical in my case because operators may not be present to adjust the pump speed'....

You can program the VFD to meet the specified set point (given that it receives pressure and flow input signals which all of them can do) so it can operate automatically.

all modern VFDs have their PLC units so you can tell them what to do.

 

[TXLSUCHE]

Thanks for your responses. I realized last night (I'm definately not an electrical engineer) after I had posted the thread that VFD's do have flow calculation capabilities. I have not been able to find any discussions on the internet concerning the use of a flow meter to control the discharge control valve, but I figured it is done fairly commonly.

 

[MortenA]

Many pump manufactor actually make (small) pumps with build in VFD e.g.

http://www.grundfos.com/web/HomeUs.nsf/Webopslag/OMAT-6MGKX9

VFD may be economical or not. Depends on your energy price. In Europe its quite high and VFD thus often favorable.

Best regards

Morten

 

[BRIS]

I think you may be confused in thinking there is a difference between a pressure control valve and a flow control valve. They are both the same. You may refer to the valve being a pressure control valve if you control it by pressure sensors or a flow control valve if you control it by a flow meter. You can do either or both if that is what best suits your application. The use of a flow meter to regulate a control valve (folomatic control) is very common.