
Guru's den : Blacksmiths Question and Answer Page
As soon as pressure rises to say about 500psi the high flow low pressure stage is by passed and the pressure rises but at a very small flow. A typical 2 stage will be say 7.3 gpm for both stages but only 1.1 at the high pressure mode. as for hp, the rule of thumb is an electrically driven pump will need about 1Hp per gpm @ 1500psi.
Read more