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