Left and right valves are provided in a lower surface of the cover on opposite sides of the seal between {HEAD ~ the partition} and {TAIL ~ the cover} 
Left and right valves are provided in a lower surface of the cover on opposite sides of the seal between { HEAD ~ the partition } and { TAIL ~ the cover }
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 HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL