When a fluid pressure in the extension chamber exceeds a certain level, the plug disengages the valve seat such that {HEAD ~ fluid} may flow from the extension chamber, in the entry port, along the relief passageway, and out {TAIL ~ the exit port} 
When a fluid pressure in the extension chamber exceeds a certain level , the plug disengages the valve seat such that { HEAD ~ fluid } may flow from the extension chamber , in the entry port , along the relief passageway , and out { TAIL ~ the exit port }
OTH 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 OTH REL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL