A differential pressure is applied across the membrane after {HEAD ~ each step} of reagent addition to {TAIL ~ the membrane} in order to remove excess reagent from the membrane 
A differential pressure is applied across the membrane after { HEAD ~ each step } of reagent addition to { TAIL ~ the membrane } in order to remove excess reagent from the membrane
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH