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