A damper valve includes a controlled flow channel between inlet and outlet sides; a controlled valve in the controlled flow channel; a movable valve body acting on the controlled valve to change a closing force of the controlled valve; and a control chamber. The control chamber includes a control chamber inlet in fluid connection with the valve inlet side upstream of the controlled valve; a configuration providing a variable volume of the control chamber, a change in volume of the control chamber moving the movable valve body; and a first flexible wall allowing movement of the movable valve body. The first flexible wall provides an effective surface area against which the fluid pressure in the control chamber acts, the effective surface area decreasing upon movement of the movable valve body outward of the control chamber, the first flexible wall including a flex plate bearing against a curved surface.