The nipple 321 is connected to a source of pressurized air, e.g., to an air compressor, which admits air, {TAIL ~ gas} or steam into {HEAD ~ the channel} 14 
The nipple 321 is connected to a source of pressurized air , e.g. , to an air compressor , which admits air , { TAIL ~ gas } or steam into { HEAD ~ the channel } 14
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH