API610 (American Petroleum Institute) and ISO design pumps are quite different in a number of ways, but very generally speaking, ISO are a lower specification pump used widely in Chemical, Pharmaceutical and Auxillary refinery installations, while API 610 is the spec covering pumps seeing higer temperature, higer pressure, and generally far more robust than ISO specifications.

It is also true to say that API610 pumps are 'specified' far too often on applications where the level of design is simply not required, and so purchase price for pumps raises tremendously.

You will find that good ISO pump manufacturers will be able to supply a deviations list of which when investigated thoroughly, will be deemed to be quite suitable for a number of applications.

general rule of thumb, API 610 heavy duty refinery pumps, ISO is refinery utilities, chemical and pharma applications.

Im sure this will prompt many replies, but in a nut shell these are the main differences !  Hope this helps...

Ash Fenn

www.cdrpumps.co.uk