In the third working chamber, there is formed an oscillating column of {HEAD ~ the working medium}, which presses against {TAIL ~ the inner sides} of both pistons 
In the third working chamber , there is formed an oscillating column of { HEAD ~ the working medium } , which presses against { TAIL ~ the inner sides } of both pistons
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH