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