The valve element also has a through passage 23 which, when arranged in an open position as shown in FIG 1, enables {HEAD ~ passage} of {TAIL ~ gas} through the valve 
of
The valve element also has a through passage 23 which , when arranged in an open position as shown in FIG 1 , enables { HEAD ~ passage } of { TAIL ~ gas } through the valve
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH