Abstract: The specification discloses a technique for controlling a pump to maintain a body of liquid below a maximum liquid level. A low voltage high frequency signal is applied to a conductive first probe which extends to a desired maximum liquid level. The high frequency signal is also applied to an electronic detector and switching circuit in order to maintain the switching circuit in a first state when the liquid level does not contact the first probe. The effect of the application of the high frequency signal to the switching circuit is reduced when the liquid level contacts the first probe, thereby changing the switching circuit to a second state. A pump is then energized to lower the liquid level in response to the second state of the switching circuit. A second probe is then coupled to receive the high frequency signal. The second probe extends to a lower level than does the first probe, thereby maintaining the pump in an energized state until the liquid level falls below the second probe.

Abstract: All of the components of a sump pump apparatus necessary to be in the sump are enclosed in a common case. In one embodiment, this case is of plastic and holds the motor means, the pump impeller and at least part of the water level sensors. The motor means is in a bell holding trapped air so that the water cannot reach the motor means. In one such embodiment the motor means is a single D.C. motor and in another embodiment it consists of a D.C. motor coupled by a one-way clutch to an A.C. motor which in turn is connected to the pump impeller. In each of these two embodiments, the water level sensor includes a tube having an open end in the bell to sample the air pressure in the bell and an end externally of the sump connected to a pressure actuated switch which turns on the motor means at a particular air pressure above ambient. Also within the bell is a float operated switch serving as a back-up to the air actuated switch. Using two motors, as mentioned above, the A.C.

Abstract: A sump pump system includes a remote pressure responsive switch assembly designed for a wall plug and having a plug in connection for the pump motor cord, the pressure responsive switch assembly also having an air pressure connection to the sump pump for actuating the switch in response to a rise in level of water around the pump.

Abstract: Pump-off control apparatus for preventing cavitation of a sub-surface pump which provides artificial lift for fluid produced from a fluid bearing strata located downhole in a borehole. A sound wave is focused downhole and travels down the casing annulus where it strikes the liquid surface and rebounds to a receiver located near the well head. The time lapse of the traveling wave is used to measure the relative location of the liquid surface relative to the pump inlet, thereby enabling the control apparatus to shut-in a well before it can encounter a pump-off condition which can cause fluid pounding.

Abstract: A compact pumping system especially useful in liquid chromatography wherein comprising a liquid path which is fully flushed on each stroke of a pump, a pump which provides substantially pulse-free flow, a pressure-sensor integrated into said flow path and operably connected to the control circuit of a bifilar stepping motor. This circuit is so designed that the driving current applied to the motor is only that required to pump the liquid. The avoiding of heat associated with a greater current is particularly important in forming a compact package of motor and pump for use in liquid chromatography.

Abstract: A liquid pump and control system for maintaining a predetermined level of liquid in a vessel comprising a liquid level sensing means, a variable displacement hydraulic pump, a control means connected to said liquid level sensing means and said variable hydraulic pump, a constant speed driving means connected to said variable hydraulic pump, a hydraulically actuated motor in fluid communication with said variable hydraulic pump and a liquid pump in fluid communication with said liquid vessel for evacuating fluid therefrom, said liquid pump connected and driven by said hydraulic motor. The liquid level sensing means within the liquid containing vessel determines the fluid level in the vessel, provides an electric signal to a variable displacement hydraulic pump which is driven by a constant speed electric motor. The variable volume output of the hydraulic pump is coupled to and drives the hydraulic motor at an RPM proportional to the pump volume.