Controllably, the chamber may be filled either with air from an external source of pressurized air or may be allowed to flood through the channel with water from {HEAD ~ the surrounding body} of {TAIL ~ water} 
Controllably , the chamber may be filled either with air from an external source of pressurized air or may be allowed to flood through the channel with water from { HEAD ~ the surrounding body } of { TAIL ~ water }
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 OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL