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