Abstract: An apparatus for indicating efficiency losses in a pump is provided. The apparatus includes a temperature sensor located at the pump input, a second temperature sensor located at a second location, a fluid flow sensor located at the second location, a processor for producing a difference signal in response to signals from the first and second temperature sensors and for quantifying efficiency losses of the pump in response to the difference signal and a signal from the fluid flow sensor. A fault indicator is also provided that is responsive to the efficiency losses.

Abstract: An apparatus is provided for detecting wear in a pump. The apparatus includes a case drain connected to the pump case, a flow sensor for producing signals indicative of case drain flow, a processor for determining whether pump wear has exceeded a predetermined level and for indicating a fault in response to the pump wear exceeding the predetermined level.

Abstract: Filter devices are useful in hydraulic systems for removing contaminants or foreign particles from the oil in the hydraulic system. One of the problems encountered with such filters is that they are subjected to high pressure drops thereacross when the oil is cold. The subject filter device of one embodiment includes a pump driven by a two-speed electric motor. When the oil temperature is below a predetermined temperature, the pump is driven at a normal speed for increased efficiency and the pressure drop across the filter is within an optimal range. When the temperature of the oil is below a predetermined temperature, the pump is driven at a low speed so that the pressure drop across the filter remains within the optimal range. In another embodiment, an electric motor driving the pump is stopped when the oil temperature is below the predetermined temperature.

Abstract: In a pump or fluid motor (11, 11a, 11b) having a closed chamber (57) in which cylinders (38) orbit and reciprocate, leakage and cooling fluid which accumulates in the chamber (57) is formed into a rotating annular volume by centrifugal effects and exhibits a higher pressure in the region where the cylinders (38) move radially inward and closer together than in the opposite region where the cylinders (38) move outward and further apart. Power wastage from drag torque, turbulence and heat generation is reduced by scavenging the accumulated fluid from the chamber (57). Internal recirculation of the scavenged fluid from the high pressure portion of the annular rotating volume back to the low pressure portion is avoided by communicating the drain passages (68, 68a, 68b) with only a limited relatively high pressure sector of the rotating volume of fluid.