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 {TAIL ~ water} from the surrounding body of {HEAD ~ 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 { TAIL ~ water } from the surrounding body of { HEAD ~ 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 TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD