Apparatus 36 includes a tube 37, having {HEAD ~ a pump} 38 at one end and {TAIL ~ gas entry pipes} 39 and 40 shown for convenience as being at the other end 
Apparatus 36 includes a tube 37 , having { HEAD ~ a pump } 38 at one end and { TAIL ~ gas entry pipes } 39 and 40 shown for convenience as being at the other end
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH