Venting device for liquid reservoir

The cap (2) has a hole (22) for air vent from the interior of a brake fluid tank (1). A casing (4) is fixed inside the cap around the hole and includes a stopper (5) in spherical shape i.e. ball. The stopper has a density less than that of a brake fluid such that if the fluid enters in the casing, the stopper floats on the fluid. The stopper is capable of plating against the hole under the pressure of the fluid.