Abstract: A pressure vessel has a container shaped housing with a top wall provided with a plurality of filter receiving openings. A bag-shaped filter element is fitted into each housing top wall opening and is retained within the top wall housing by a hold-down ring having one of its ends pivotally secured to the top wall to permit the ring to be moved between a first position overlaying a portion of each filter to retain the filters in position within their respective top wall openings and a second position wherein the ring is pivoted upwardly from the housing top wall to permit the removal of each filter bag. A cover encloses the pressure vessel at the top wall section and the interior of the cover forms a flow path between an inlet and the filter bags such that liquid to be filtered passes from the inlet downwardly through the filter bags and into the interior of the housing beneath the top wall and is exhausted through a liquid outlet provided in the housing.