A device for recovering energy with rankine loop including: - a heat exchange loop with a heat source in which a working fluid circulates, - an expansion member disposed in the loop able to transform energy originating from the expansion of the fluid into mechanical energy, - a bypass circuit of fluid connecting the upstream of the expansion member to the downstream of the expansion member, - means for transmission of the mechanical energy produced by the expansion member, this device being characterized in that it includes in addition: - blocking means of the transmission means, - control means of the blocking means, - a passive non-return valve calibrated to a specified calibration force and disposed in the bypass circuit, - the control means and the valve being designed to cooperate such that: ∘ when the power available to the heat source is less than a specified power threshold, the control means block the transmission means, such that the pressure of the fluid in the loop increases until exerting on the valve a force greater than the specified calibration force, the valve then opening to permit passage of the fluid in the bypass circuit, ∘ when the power available to the heat source is greater than the specified power threshold, the control means do not block the transmission means, so that the pressure of the fluid in the loop reduces until exerting on the valve a force of the fluid on the valve less than the calibration force, the valve then closing to prohibit the passage of the fluid in the bypass circuit. - a heat exchange loop with a heat source in which a working fluid circulates, - an expansion member disposed in the loop able to transform energy originating from the expansion of the fluid into mechanical energy, - a bypass circuit of fluid connecting the upstream of the expansion member to the downstream of the expansion member, - means for transmission of the mechanical energy produced by the expansion member, - blocking means of the transmission means, - control means of the blocking means, - a passive non-return valve calibrated to a specified calibration force and disposed in the bypass circuit, - the control means and the valve being designed to cooperate such that: ∘ when the power available to the heat source is less than a specified power threshold, the control means block the transmission means, such that the pressure of the fluid in the loop increases until exerting on the valve a force greater than the specified calibration force, the valve then opening to permit passage of the fluid in the bypass circuit, ∘ when the power available to the heat source is greater than the specified power threshold, the control means do not block the transmission means, so that the pressure of the fluid in the loop reduces until exerting on the valve a force of the fluid on the valve less than the calibration force, the valve then closing to prohibit the passage of the fluid in the bypass circuit. ∘ when the power available to the heat source is less than a specified power threshold, the control means block the transmission means, such that the pressure of the fluid in the loop increases until exerting on the valve a force greater than the specified calibration force, the valve then opening to permit passage of the fluid in the bypass circuit, ∘ when the power available to the heat source is greater than the specified power threshold, the control means do not block the transmission means, so that the pressure of the fluid in the loop reduces until exerting on the valve a force of the fluid on the valve less than the calibration force, the valve then closing to prohibit the passage of the fluid in the bypass circuit.