A filter assembly comprising: a manifold having a fluid inlet and a fluid outlet, a filter housing having a filter medium provided therein, the filter medium defining an inner filter chamber and defining an outer filter chamber between the filter medium and the filter housing, the filter housing being removably attached to the manifold so as to provide a fluid flow path from the inlet into the inner filter chamber, through the filter medium into the outer chamber and out of the outlet; characterised by the filter assembly further comprising a valve assembly mounted inside the manifold, the valve assembly comprising a valve piston and a valve spring arranged in engagement with the valve piston to bias the valve piston into a first position, in which fluid flows from the fluid inlet into the inner filter chamber, through the filter medium into the outer chamber and out of the fluid outlet, and to compress, in response to a pressure differential across the valve piston exceeding the spring force, to move the valve piston to a second position being a bypass position in which a bypass channel is opened to direct flow from the fluid inlet to the fluid inlet without passing through the filter medium, the valve assembly further comprising an adaptor ring located between the valve piston and the filter housing and provided with an annular seal, and wherein the valve piston is provided with a radially extending flange and an inner piston wall configured such that as the filter housing is being detached from the manifold, the valve spring expands to move the valve piston to a third, shut off position whereby the piston flange is in sealing engagement with the adaptor ring and the outlet seal and the inner piston wall is in sealing engagement with inlet seals such that flow from the inlet and the outlet is shut off from entering the filter housing; and wherein the valve spring is located in a blind cavity outside of the path of fluid flow through the assembly. a manifold having a fluid inlet and a fluid outlet, a filter housing having a filter medium provided therein, the filter medium defining an inner filter chamber and defining an outer filter chamber between the filter medium and the filter housing, the filter housing being removably attached to the manifold so as to provide a fluid flow path from the inlet into the inner filter chamber, through the filter medium into the outer chamber and out of the outlet; characterised by the filter assembly further comprising a valve assembly mounted inside the manifold, the valve assembly comprising a valve piston and a valve spring arranged in engagement with the valve piston to bias the valve piston into a first position, in which fluid flows from the fluid inlet into the inner filter chamber, through the filter medium into the outer chamber and out of the fluid outlet, and to compress, in response to a pressure differential across the valve piston exceeding the spring force, to move the valve piston to a second position being a bypass position in which a bypass channel is opened to direct flow from the fluid inlet to the fluid inlet without passing through the filter medium, the valve assembly further comprising an adaptor ring located between the valve piston and the filter housing and provided with an annular seal, and wherein the valve piston is provided with a radially extending flange and an inner piston wall configured such that as the filter housing is being detached from the manifold, the valve spring expands to move the valve piston to a third, shut off position whereby the piston flange is in sealing engagement with the adaptor ring and the outlet seal and the inner piston wall is in sealing engagement with inlet seals such that flow from the inlet and the outlet is shut off from entering the filter housing; and wherein the valve spring is located in a blind cavity outside of the path of fluid flow through the assembly.