To BPO or not BPO ? – that is the question

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Back Pull Out

When selecting centrifugal pumps for air conditioning circuits, it’s good to be “fluid” in your decision making – after all, that’s what we’re dealing with.

We would all agree that the Back Pull Out (BPO) pump is a versatile and preferred selection when it comes to chilled, heating and condenser water circuits; they offer flexibility in allowing impeller changes within the same casing without having to disturb the pipework or change the electric motor if originally sized correctly.

This always made the BPO the preference when designing air conditioning systems.

However, this should not be a given. There are times when BPO pumps are not the best option.

This is particularly so on small flow rates.

Take for example a duty of 2 litres per second @ 200kpA.

If we plot this duty on a BPO type pump curve, be it DIN or ISO standard, it will be found to be a relatively flat curve. This will make it difficult to balance the system. A steep curve is always preferable.

So in this case a smaller pump running at 2 pole speed such as the SV or HMS series (pictured) are a better selection.

They use less power, being smaller yet have the same level of efficiency as the BPO which at this low duty point will always be low as a function of centrifugal design.

This will offer a space saving due to having a smaller foot print. Installation costs will be reduced, making the process simpler and more economical.

The noise factor is often raised as being a higher speed unit, it is often assumed they would be noisy.

Materflow tested the SV4 on our testing rig in the presence of an acoustic engineer for the COM Project some five years ago.

The SV4 met the acoustic requirements on this sensitive project and as a result, a dozen were installed and have been pumping merrily ever since.