Progressing cavity pumps minimum flow 1

[Sam1390]

Hi everyone,
I have some PC pumps at the sludge lines of a waste water treatment plant, we are preparing data sheets for vendor.
the pumps mainly have VSDs. the material balance table shows a few different flow conditions.

I am mentioning the design data based on the maximum flow. just wondering if any minimum flow is required to be mentioned for vendor.

please note , there are a number of pumps working in parallel , so if required they can out of service.

Cheers,
Sam

 

[georgeverghese]

Control min flow in this case would be the flow at the VSD speed turndown limit. Assuming each pump has its dedicated min flow control loop. Control loop would be configured as high set discharge pressure kickback. To enable testing of any pump at max flow, you could install a manual globe valve as a bypass to the high set kickback PCV.

 

[LittleInch]

I think it's more of a motor issue about whether at the low flow there is enough power from the motor.

So does your head requirement change with flow?

I don't think the is any harm in mentioning different flows and heads based on a VFD control.

PC pumps are PD pumps so not sure why you want to vary flow? Can't you just pump for a shorter time?, I.e. why have the VFD? Process engineers sometimes don't think about practical issues or doing things cheaper and easier.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[FacEngrPE]

I had a situation where I replaced a control valve and a centrifugal pump with a progressive cavity pump and a VFD, to provide a constant flow rate. The head at the pump varied from forward direction 26 ft, to reverse direction 5 ft. This works only if the VFD is provided with a braking resistor to sink excess energy.

Your case - is likely to have problems with the motor needing to operate at low speed but full load torque. Motors can be ordered for this duty, but are not off the shelf. Recommend you discuss with your motor suppliers engineering department.

Positive displacement pumps like progressive cavity pumps do not suffer from low flow cavitation or vibration, but can experience full load torque at zero speed, which requires special motors (if your application requires low speed operation).