A fluid flow delivery system switches a variable speed pump drive among a plurality of pumps. The remaining pumps can be operated as constant speed pumps and can be energized one at a time in response to increasing demand. The pump associated with the variable speed drive can be operated over a variable output range to provide relatively low levels of fluid output, in response to low demand, and can be operated in combination with one or more constant speed pumps to provide increased levels of output fluid in response to greater demand levels.