According to the Specifications for the Clack valve ( (click on Control valve and pick the valve of interest) The 1" Clack valve alone will cause a 15 psi pressure drop at 27 gallons per minute flow while in service. In my opinion if you go with a 1" valve you will never see 44 gallons per minute flow in your system. If you really want a flow of 44 gallons per minute you will need a 1.5 inch valve.