Liquid level sensing device and swimming pool water circulation systems containing the same

A liquid level sensing and control device comprising, in combination, a U-tube having substantially vertical legs connected by another member putting the legs in fluid flow intercommunication at their lower ends;

• a variable capacitor in one leg of the U-tube, comprising two spaced electrodes;
• 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 line connection putting said third body of liquid into contact with a fourth body of the same or different liquid whose liquid level is to be sensed, the third body moving in the U-tube to a changed position in response to change in hydrostatic fluid pressure communicated from the fourth body to said third body as a function of fluid level of the fourth body so that the relative level of said first body of first liquid in the space between the electrodes in the variable capacitor is related to liquid level in said fourth body, communicated as fluid pressure via the fluid pressure communication to said third body, the third body thereby moving the second body of liquid and the second body of liquid moving the first body of liquid in the U-tube to a level related to liquid level in said fourth body, and corresponding to a capacitance of the variable capacitor;
• and means sensing at least one selected capacitance of the variable capacitor and initiating a control reaction responsive thereto.