{TAIL ~ A pipe} which can be shut off by a solenoid valve is provided to feed ammonia gas into {HEAD ~ the mixing chamber} of the regeneration system  
{ TAIL ~ A pipe } which can be shut off by a solenoid valve is provided to feed ammonia gas into { HEAD ~ the mixing chamber } of the regeneration system
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH