Transfer pumps are typically used to fill water storage tanks, and as this is a task you most likely just want done as quickly as possible, a fixed speed pump is perfect for the job, while paying for a variable speed motor is an unnecessary expense in a transfer pump. The pump must also be able to start and stop automatically according to demand in the tank, which is often solved by using a float valve. If the highest tapping point, Hmax is above the start pressure the pump will never start and choosing a pump with an additional external input that can be fitted with a float switch is therefore recommended.