Abstract: A filter arrangement for a single acting, telescopic, hydraulic cylinder, useful to raise and lower a dump truck bed, is configured for installation in one line of a two-line dump pump to filter only hydraulic fluid returning to sump. This is accomplished by a first one-way check valve which blocks fluid flow through a filter element toward the hydraulic cylinder but allows fluid flow from the hydraulic cylinder to sump and a second one-way check valve, disposed in parallel with the filter element, to block flow to the sump from the hydraulic cylinder while allowing flow from the sump to the hydraulic cylinder so that returning hydraulic fluid passes through the filter element. Preferably the filter element is disposed in a spin-on filter assembly which includes the one-way check valves integral therewith.