Nicole,

Actually, you can put the valve at anypoint after the pump. Head loss is additive and does not really matter where it occurs. Any restriction affects the entire flow path GPM so find an easy place to put it in the return path. However, if you place it after the filter, you can more easily adjust the flow by watching the filter PSI rise. You do not need to worry about pump damage as long as you keep the PSI rise to less than 10 and the total rise to less than pump maximum, usually 35 PSI but I would not exceed 25 PSI. Note that the restriction PSI is similar to puting solar in.