Abstract: An upwardly pyramidal frame, formed of angularly spaced legs converging to a point, is mountable on a holder that extends about a fill opening of the pressure tank of a blast cleaning system. The frame is so disposed as to break open the end of a bag containing an abrasive media, when the bag is dropped onto the frame, with the break occurring at a location confined to the area of the fill opening. A screen supported upon a shoulder of the holder extends across the opening. At the bottom of the frame, outwardly directed feet on the legs extend into a space between the shoulder on which the screen is supported, and opposing, downwardly facing shoulders. Screws threaded in the feet bear against the peripheral portion of the screen, to clampably engage the feet and the screen against the opposed shoulders. When a screen is to be replaced, the screws are backed off, to loosen the frame and screen and permit their removal and replacement.