Forklift- why do you believe these style cylinders are not true "differential"? The theory of operation is that oil, which is top of the bottom packing (by design), goes thru the valve on the bottom of the ram when the rod begins to move upward, mixing with the incoming oil, increasing pressure & volume under the ram allowing the ram to move faster & have more pressure behind it than is supplied from the hyd. pump.
The upper gland nut on these type cylinders has packing installed, not just a wiper.
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