Each module has {HEAD ~ a housing} divided by {TAIL ~ walls} into a transfer chamber at one end and a second chamber at the other end 
Each module has { HEAD ~ a housing } divided by { TAIL ~ walls } into a transfer chamber at one end and a second chamber at the other end
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH