This invention relates to water purification systems and in particular to a control for a system of the type that purifies water by converting it into steam and condensing the steam back into water.
Water distillation systems are well-known in the art and include a boiling tank having an inlet for admitting untreated feed water to the tank and heating means for heating the untreated water to produce steam. As steam is generated by the boiling tank, the minerals and other impurities in the residue water increase in concentration. Periodically, it is necessary to remove the residue by draining. In a water distillation unit designed for domestic home use, the drain commonly discharges the residue water into the house drain. With the advent of polyvinylchloride plastic pipe for plumbing systems, it is necessary to reduce the temperature of the residue water before discharging it to the drain. Accordingly, one object of the present invention is to provide an efficient and inexpensive means for reducing the temperature of the residue water before it is discharged to drain.
Even if the residue is periodically discharged to drain, mineral scale will be deposited on inner surfaces of the tank and outer surfaces of the heater. Accordingly, it is necessary to periodically shut down the unit and descale the interior of the boiling tank by filling the tank with water having descaling chemicals added thereto and, after a soaking period, draining the cleaning liquid and rinsing the tank. It is an object of the present invention to provide a control having a cleaning mode that minimizes the complexity of the procedure performed by the user and that adds very little to the cost of the control.
The primary purpose of a water distillation unit is to produce distilled water and accumulate this water in a holding tank until needed for use. Consumers expect that such water will be of very high quality. If the water in the holding tank is contaminated by the condition of the holding tank then water quality may be diminished. Accordingly, it is known to disable the condensing portion of the water distillation apparatus in order to provide steam from the boiling tank directly to the holding tank in order to destroy microorganisms that may be established in the tank. The difficulty with known units having such a steam cleaning cycle is that, if the user forgets to reactivate the condensing means, then the steam will eventually condense within the holding tank providing a buildup of very hot water in the holding tank. If the holding tank outlet pump is operated by the user after inadvertently neglecting to discontinue the steam cleaning mode, it is possible that the hot water may cause damage to the holding tank outlet pump. Accordingly, it is an object of the present invention to provide an inexpensive control for protecting a water distillation unit against the failure of the user to discontinue the steam cleaning mode.
Another difficulty with water distillation units is that the addition of relatively cold untreated feed water to the boiling tank tends to rapidly lower the temperature of the interior of the tank. This lowering of temperature creates a vacuum within the boiling tank which tends to draw water already condensed in the condenser and steam previously produced back into the boiling tank where it will condense back into water. Therefore, the addition of feed water creates inefficiencies in the operation of the unit which results in increased energy consumption per unit of water produced. Accordingly, it is an object of the present invention to provide a control for a water distillation unit which carefully controls the frequency and amount of feed water admission to the boiling tank in order to reduce the detrimental affects described above.