The unit may also have {TAIL ~ a tubing} to allow oxygen or {HEAD ~ another treated gas} to come in 
The unit may also have { TAIL ~ a tubing } to allow oxygen or { HEAD ~ another treated gas } to come in
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH