Apparatus for visually indicating when a pool filter is dirty

Apparatus for indicating when a swimming pool filter needs to be cleaned, comprising a conduit member adapted to be connected to the inlet side of a pool filter for directing water into the filter, the conduit having an opening along the side, means projecting around the opening forming a flat surface, a diaphragm of flexible material in contact with said surface and extending across the opening, housing means covering the diaphragm and clamping the diaphragm against said surface, a piston member movably supported in the housing means, the piston member having a surface engaging the diaphragm, spring means urging the piston surface and diaphragm toward the conduit against the pressure exerted against the diaphragm by water in the conduit, the housing means having a window therein, a pivoted flag positioned adjacent the window, and linkage means connecting the piston means to the flag for moving the flag in response to movement of the piston means, the flag being movable between a position viewable through the window and a position out of view through the window, the linkage means moving the flag into the viewable position when the piston means moves against the urging of the spring a predetermined distance, the piston means including a hinged member extending across said opening with one side in contact with the diaphragm, the linkage means being pivotally connected at one end to the flag means and at the other end to the hinged member, the linkage means including lost motion means for allowing the hinged member to move a predetermined distance before it begins to move the flag through the linkage means.