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