For Vo less than zero, {TAIL ~ oxygen} is pumped back into {HEAD ~ chamber} 28 of FIG 1 
For Vo less than zero , { TAIL ~ oxygen } is pumped back into { HEAD ~ chamber } 28 of FIG 1
OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH