The systems and methods of the present disclosure provides an independent passive variable resistor that can be interposed between a fluid reservoir at an inlet pressure and receptacle at an outlet pressure. The resistor can adjust resistance to the pressure difference from the input to the output so that the flow rate through it is a constant rate. The resistor can include a moveable element and a biasing mechanism located in a chamber to create a flow channel. Each side of the moveable element is exposed to the inlet and outlet pressures and moves within the flow channel to modify the resistance of the flow through the chamber in response to the pressures. The balance of these forces determines the position moveable element, which interacts with the fluid channel to determine the flow resistance through variable resistor. The biasing mechanism can provide the necessary pressure to establish equilibrium flow rate.