At the pressure side of the pump unit, there is {HEAD ~ a valve} which opens during {TAIL ~ certain times} to form a connection between the pump and the pump station to create a circulation 
opens during
At the pressure side of the pump unit , there is { HEAD ~ a valve } which opens during { TAIL ~ certain times } to form a connection between the pump and the pump station to create a circulation
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH 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