First of all, the pump style is usually dictated by the service in which the pump is to operate.

For low pressure cold water, we would normally be looking at a general service pump.

For high pressure/high temperature hydrocarbon service, a pump designed in accordance with API 610 specifications.

For low temperature chemical services, the ANSI pump design would be considered.

At that point the Head-Capacity conditions would provide the selection.

To determine the speed of the pump, this is frequently decided by economics as the higher speed pumps are usually smaller and less costly.

However, this must be tempered with the NPSH Available as the higher speed pump will require more NPSH than the lower speeds.