Respectfully, I spent my entire career in this field, if you look at it logically if the piston moves down and oil bypasses the packing and it has nowhere to go and cannot go back through the valve on the rod end pressure builds and equalizes on both sides of the piston and the rod stops, the real effect is that the surface area of the cylinder becomes simply the rod diameter, I have seen this many times and after you have spent as many hours 50+ years you will agree with me, now keep in mind the rod can pull out if enough pull is put on it as it will create a void in the butt end of the cylinder, that is why modern valves have a regeneration circuit built in to allow return oil back into the supply. The only way the rod can retract is if the rod end supply hose is loosened so the pressure created in the rod end caused by more volume of oil in the piston end than the rod end can accept causes the pressure buildup that keeps the rood from further retraction. I remind you, I spent my life ar this stuff. In my career I have had phone calls from Case Service personell to discuss hydraulic issues. When at my job I could find a leaky packing in a cylinder by heating the oil and feeling around the barrel for hot spots where the oil was bypassing, I did not need pumps, I found problems in bugged machines at service schools that the instructor said could not be found without a flowmeter. On a dual loader lift cylinder system a piston seal leak on one cylinder will allow about 4-6 inches of down drift before the pressures equalize after releasing the spool. Piston seal leakage can often be found by holding the hydraulics against relief with hot system oil and feeling the barrel where the piston is and the leak will be apparent by a hot spot on the barrel, on any of these problems your senses are your best friend. BTW I do believe in flowmeters for system diagnosis,in fact we flow tested all new backhoes and recorded the results as a baseline for future reference and it has bailed us out in a few instances.
