Abstract: A filter assembly is provided for fitting to an aperture in the wall of an oil tank of a hydraulic system with a disposable filter canister positioned substantially within the tank. The canister comprises a shell having an end wall and a generally cylindrical side wall, an end plate attached to the shell, a tubular filter element fluid-tightly fitted between the end wall and the end plate to define an outer chamber and an inner chamber between which the only flow path is through the filter element. The end plate has a central aperture communicating with the inner chamber and surrounded by a ring of apertures communicating with the outer chamber. A filter head is fluid-tightly fitted to the outer face of the tank wall in register with the aperture.