Specific speed calculation

[Wkcoo]

Hi, wondering what's the usual convention to calculate specific speed for double suction impeller, whether to halve the flow or not?

I am referring to Fraser's article on minimum flow that splits into two graphs depending on specific speed, but it didn't discuss on the convention he used to calculate the specific speed.

 

[Artisi]

Discharge specific speed Q
suction specific speed Q/2.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)