Controlled volume pumps capacity control

[vjr0512]

For the Chemical dosing packages where mostly controlled volume (diaphragm type) pumps are used, for the capacity control, the stroke of the pump is varied either by manual or automatic ( motorised actuator) . Client prefers to have VFD for the capacity control as they have experienced problems in the stroke control methods said above. Whether the above proposal for providing VFD for capacity control for a PD pump is efficient than the stroke control? Thanks to clarify.

 

[1503-44]

Both methods are effective, given the correct pump selection, and can be used separately or in combination.

 

[LittleInch]

a lot will depend on the turndown / range required and the pressure you need.

VFDs have a certain range, but then at the lower end can reduce torque and might stall.

With a variable stroke you have a higher range and no issues wrt pressure

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

 

[ashtree]

You also need to look at how the whole system is configured and whether a less frequent larger dose of chemical is okay when compared to more frequent smaller doses. If you are simply dosing into a large well mixed tank, probably will cause no issues. But if you are dosing straight into some process and there is inadequate mixing maybe this will be a problem.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[bimr]

The new VFD controls on metering pumps result in a metering pump system that has twice the accuracy over a turndown ratio ten times greater than traditional designs.

This is discussed in this brochure:

Link

 

[vjr0512]

Thanks a lot for all the wonderful answers. bimr, whether Milton roy is the only vendor who supply this VFD drive controlled volume pumps? Unless we require the turndown less than 10%, the milton roy option would be a costly proposal i suppose.

 

[SB1976]

While VFD is generally okay for capacity control, please bear in mind that turndown is rather limited for VFD (~50%). This is because when VFD is directed to operate at lower speeds, huge losses are encountered in the motors, which manifests in high heat generation. Hence, for operation less than 50% speed, VFD manufacturers'invariably recommend/provide heat exchangers to mitigate the problem, which results in higher cost.

Hence, given a choice, I would personally not go for a VFD. I would rely on capacity control by inherent means. I would probably frequent recalibration of the CV pumps to ensure not missing out on accuracy / efficiency.