Abstract: A vacuum filter for vacuum flow filtration through a filter bed of water from a swimming pool is provided, comprising an open-top tank; a filter bed of particulate material in the tank; fluid flow connections communicating the tank with a water recirculation system for the swimming pool, one adjacent an upper portion and one adjacent a lower portion of the filter bed; an inlet line communicating the swimming pool with the tank and maintaining the level of water in the tank at a level corresponding to a level of water in the swimming pool, thereby providing a head of water for gravity backwash flow through the filter bed, and valves controlling flow into the tank via the fluid flow connections between the tank and the inlet line, and between the tank and the water recirculation system; and a direct fluid flow connection communicating a gutter drain of the swimming pool with the tank; a vacuum is drawn downstream of the filter bed by a pump recirculating filtered water to the swimming pool.

Abstract: A liquid level sensing device is provided comprising, in combination, a U-tube having two substantially vertical legs in fluid interconnection at their lower ends; a variable capacitor in one leg of the U-tube, comprising two spaced electrodes receiving a dielectric liquid therebetween; a first mobile body in said one leg of a first dielectric liquid capable of rising and falling within the space between the electrodes and to a level at which it partially or fully fills the space; a second mobile body in said one leg of a second liquid having a higher density than and immiscible with the dielectric liquid, and having an upper surface on which rests the first body of dielectric liquid; a third mobile body in the second leg of a third liquid immiscible with the second liquid and disposed in operative relationship with the second body of liquid; and a fluid pressure communication between said third body and a fourth body of the same or different liquid whose liquid level is to be sensed, so that the relative lev

Abstract: An integrated monitor and control system for continuously monitoring and controlling pH and free halogen concentration in swimming pool water is provided, comprising, in combination, a first electrochemical flow cell having two electrodes and through which swimming pool water flows, giving rise to an electric potential between the electrodes in proportion to hydrogen/hydroxyl ion concentration in the pool water; means for measuring the electric potential across the electrodes in a manner correlated with pH of the pool water; a second electrochemical flow cell having two electrodes and through which swimming pool water flows giving rise to an electric potential between the two electrodes in proportion to the oxidation/reduction potential of the pool water; means for measuring the electric potential across the electrodes in a manner correlated with halogen concentration in the pool water; a first operational amplifier in electric connection with the first cell and arranged to respond to a pH outside a predeterm