When gate 15 is moved upwardly to open the valve, to bring gate passage 35 into alignment with body passages 25, 26, {HEAD ~ the cam action} between pins 44 and grooves 45 causes {TAIL ~ movement} of element 41 away from the gate to deactivate the seal formed by seal element 49 
causes
When gate 15 is moved upwardly to open the valve , to bring gate passage 35 into alignment with body passages 25 , 26 , { HEAD ~ the cam action } between pins 44 and grooves 45 causes { TAIL ~ movement } of element 41 away from the gate to deactivate the seal formed by seal element 49
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH