The body portion 15a is formed into {HEAD ~ a generally circular columnar shape}, and is provided at its upper portion with {TAIL ~ a gas exit} 15b 
The body portion 15a is formed into { HEAD ~ a generally circular columnar shape } , and is provided at its upper portion with { TAIL ~ a gas exit } 15b
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH