What are common issues when using progressive cavity pumps as dosing/metering pumps?

[MartinLe]

I work in the Biogas field, we pump a lot of slurries (either literally cattle slurry/liquid manure or mixtures of water, slurry with energy crops) in a range up to 14%TS
metering flow via MID is challenging with these organics loads.

Now, one could isntall a revolution counter on the shaft of a progressive cavitiy pump and should, in theory, be able to measure the flow with great precision (for our causes).

The only issue I see would be leakage along the sealing line if operating against high pressure.

I'm trying to understand the possible issues - what am I missing?

 

[pennpiper]

You are only missing some controlled tests to validate your hypothesis.

prognosis: Lead or Lag

 

[Pumpsonly]

PC pump can not be use for accurate metering purposed if the pressure fluctuates. If you have look at a PC pump performance curve,
the flow rate actually decreases quite significantly with increasing diff.pressure especially toward the end of the diff. pressure capability. Unless you use a high diff. pressure pump for a low pressure application.

 

[DubMac]

PC pumps can be used as metering/dosing pumps if they are properly applied. The issue to be concerned with is "slip"; that portion of the flow which "slips" back to suction during displacement. No positive displacement pump has 100% volumetric efficiency (except maybe a bucket); and of course the VE does change with pressure, and also with varying fluid characteristics, and pump wear, etc. But the slip variation with pressure is known and can be had from a competent manufacturer....if you talk nice enough to them.

If a competent PC manufacturer is made as fully aware of your particular service as possible, they will be able to define the slip extremely closely; usually within the precision required. They will play with the various combos of rotor and stator materials, and speed, to control slip for your service.

However, per Pennpiper, nothing is more accurate than actual field calibration measurements.

 

[MartinLe]

I forgot to mention that some collegues tried something similiar this at a running plant (where we also have an IDM downstream of the pump), but I couldnt pester them for details yet.

Pressure should be stable and in the lower range of the working range of the pump, material consistency varies over the year and maybe also over the day.

Thanks for your input, I'll check back when I had a chance to talk to my collegues.

 

[mirghaffari]

as i khnow, progressive cavity pumps API 676) can not use as meetering pumps.it is better you use meetering dosing pumps for this application

 

[DubMac]

The people at Seepex may disagree with you.

 

[Pumpsonly]

Not only Seepex, many others PC pump makers will disagree as well. It is a matter of what accuracy you are looking for and how long you can maintain that accuracy.

 

[MortenA]

Guy you also have to consider the application - its manure! High accuracy is maybe not that important? Why must it be metered? Is it loaded into truck - and metering is required so that they do not overfill, or is it for paymeent/tariff for the farmer that delivers?

Best regards

 

[TenPenny]

It certainly depends on the accuracy desired, but based on what you've given, I'd assume that a high degree of accuracy isn't needed (ie, you're not dosing chlorine into water or anything like that), and my first suggestion would be to use a PC pump. I think it would do exactly what you need.