The liquid solution to be separated is pumped past {TAIL ~ the membrane} at {HEAD ~ a controlled pressure} 
The liquid solution to be separated is pumped past { TAIL ~ the membrane } at { HEAD ~ a controlled pressure }
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD