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