Abstract: The present invention relates to pool filters. An underdrain design is disclosed that primarily relies on a peripheral ring rather than lateral projections to transfer the water to the sand. The ends of the ring are not joined so that the ring is not closed. The ring is also bent into a helical shape which allows the ring to be screwed into an opening with a smaller diameter than that of the ring. The ring is radially slotted so that water flows radially from it in all directions both toward the center of the tank and away from the center, as well as straight up and down. Since the water transfer takes place primarily along an arc located relatively near the mid-point between the center and the perimeter of the tank, the disadvantages inherent in the concentration of the water flow at the center of the tank are eliminated.

Abstract: There is disclosed an electro-mechanical door opening and closing device which is adapted to be retro-fitted onto an existing manually operated sliding door system. The sliding door system has a stationary panel and a movable panel and the system is installed in a wall of a building. A stationary portion includes the stationary panel, the door frame and the building adjacent to the door frame. The device includes a reversible motor, a bracket or handle and a control system. The reversible motor is attachable to one of the stationary portion and the movable panel. The bracket is attachable to the other of the stationary portion and the movable panel. The device includes a threaded rod operably connected to the reversible motor such that the rod may be rotated clockwise and counterclockwise. The rod is also movably connected to the bracket and rotation of the rod clockwise and counterclockwise causes the bracket to move towards and away from the motor thereby opening and closing the sliding panel.