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