The invention provides {HEAD ~ a back up supply}, by putting {TAIL ~ the air} through a plenum chamber and dividing it so that when cooling airflow is reduced, a further sealing air flow is provided in compensation therefore 
by putting
The invention provides { HEAD ~ a back up supply } , by putting { TAIL ~ the air } through a plenum chamber and dividing it so that when cooling airflow is reduced , a further sealing air flow is provided in compensation therefore
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH