The differential valve piston comprises working surfaces of at least two different diameters such that changes in {TAIL ~ chamber pressures} effect {HEAD ~ different axial forces} upon the piston 
The differential valve piston comprises working surfaces of at least two different diameters such that changes in { TAIL ~ chamber pressures } effect { HEAD ~ different axial forces } upon the piston
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH