Handbook on Test Development: Helpful Tips for Creating Reliable and Valid Classroom Tests

A pop-up swimming pool cleaner comprising a cleaner for a swimming pool having a floor formed with an opening therein, said cleaner comprising a nipple that is positioned within the opening and clamped to the bottom wall. This nipple is internally threaded and screwed thereinto is the top wall of a gear housing. This top wall is formed with a central opening in which is journaled a tube which opens at its upper end into a vertical arm of an L-shaped passage and the lower end of which is splined. The gear housing includes an outer cylindrical wall and a bottom wall. It also includes an inner cylindrical wall extending between the top and bottom walls, and an annular wall spaced from the top wall defines a chamber for a rotor having a central tubular member extending into the inner cylindrical wall of the gear housing. This member has interior splines at its lower end and the tube which extends through the top wall also extends into this tubular member and is formed with external splines, with the rotor and tube being formed with abutment means for limiting axial movement of the splined tube. The rotor includes an internally toothed ring gear and meshing therewith is a pinion above the annular wall. This ring gear constitutes the upper end of a reduction gear train.