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