Abstract: An energy storage system includes a vessel, an energy conversion device, and a connection line connecting the vessel with the energy conversion device. The energy conversion device includes a housing, a pump turbine, and a motor generator. The pump turbine includes a first shaft, and an impeller. The motor generator includes a second shaft, and a rotor. The second shaft is coupled to the first shaft to transmit torque between the first shaft and the second shaft. The connection line connects a low pressure opening with an opening disposed at the vessel to receive water from the vessel or discharge water into the vessel. The connection line includes a switching unit with a shut-off device and a non-return device connected in parallel, the non-return device enabling flow of the water only in a first direction from the vessel to the low pressure opening.

Abstract: A pump device, in particular an immersible pump device, includes at least one heat exchanger unit which is in at least one operation state configured for a heat exchange between a cooling fluid and a liquid that is to be pumped and which includes at least one cooling duct and at least one shaft receptacle having an axial direction, wherein a cross section surface area of the cooling duct changes by maximally 200% at least over a major portion of a course of the cooling duct.

Abstract: A pump device, in particular an immersible pump device, includes at least one heat exchanger unit which is in at least one operation state configured for a heat exchange between a cooling fluid and a liquid that is to be pumped and which includes at least one cooling duct and at least one shaft receptacle having an axial direction, wherein a cross section surface area of the cooling duct changes by maximally 200% at least over a major portion of a course of the cooling duct.

Abstract: An operating method for a pump includes providing a return line for returning the fluid from a high-pressure side to a low-pressure side, controlling a control valve in the return line with a surge control unit for avoiding an unstable operating state, the control valve controlling the throughflow through the return line, storing a limit curve for a control parameter in the surge control unit, comparing an actual value of the control parameter with the limit curve during the operation of the pump; and when the actual value of the control parameter reaches the limit curve, controlling the control valve in the return line such that the actual value of the control parameter is moved away from the limit curve, an operating parameter of the pump being used as the control parameter.

Abstract: An operating method for a pump includes providing a return line for returning the fluid from a high-pressure side to a low-pressure side, controlling a control valve in the return line with a surge control unit for avoiding an unstable operating state, the control valve controlling the throughflow through the return line, storing a limit curve for a control parameter in the surge control unit, comparing an actual value of the control parameter with the limit curve during the operation of the pump; and when the actual value of the control parameter reaches the limit curve, controlling the control valve in the return line such that the actual value of the control parameter is moved away from the limit curve, an operating parameter of the pump being used as the control parameter.