A valve unit for an anti-lock braking system

A valve unit for an anti-lock braking system of a vehicle, comprising:

• a valve body with a delivery port that hydraulically connectable to a brake caliper, an inlet port hydraulically connectable to a master cylinder, an axially elongated internal cavity hydraulically connectable to the inlet port and the delivery port, an expansion chamber expandable in contrast to a spring element, an outflow passage between the axially elongated internal cavity and the expansion chamber, and a non-return valve arranged between the expansion chamber and the inlet port;
• a cutoff piston, axially movable in the axially elongated internal cavity in contrast to an action of an associated elastic element,
• sliding contact sealing elements arranged at an interface between the cutoff piston and the axially elongated internal cavity, defining with the cutoff piston and with the axially elongated internal cavity an axially movable hydraulic chamber;
• wherein the cutoff piston is movable between two alternative axial positions:
• a first axial position, in which the cutoff piston compresses the associated elastic element, and moves the axially movable hydraulic chamber placing the axially movable hydraulic chamber in fluid communication with the expansion chamber and the delivery port, and not with the inlet port, and
• a second axial position, in which the associated elastic element is released and the cutoff piston places the axially movable hydraulic chamber in fluid communication with the delivery port and the inlet port, and not with the expansion chamber.