where should a check valve be installed

I have a Purex SM 4000 filter and a wisperflo pump with a chlorinater no heater I have a pentair Flapper check valve (the inside the piping type) a foot above the pump outlet between the filter inlet, the clorinater is on the outlet side of the filter. When the flapper goes bad I lose some of the prime in the pump. Should I have a check valve on the inlet side of the pump ? The pump will prime up in about 10-15 seconds and work fine but I have to bleed the air out of the filter 10 seconds.