A cap (20) for a header box of a heat exchanger (1), in particular for a motor vehicle, in particular a radiator, is disclosed. This cap includes a head (21), a shank (22) comprising at least one mounting thread (23), this shank being between the head and a free end of the cap, a retaining lug (30), in particular elastically deformable, arranged to retain the cap in an opening (10) of the header box in an intermediate position of the cap, in which position the cap leaves a clear passage while being retained in the opening, this retaining lug being formed on the shank.

A pressure cap for a cooling system of a vehicle may include a reservoir fill port which is mounted at an upper portion of a reservoir in which cooling water is stored in a cooling system of the vehicle; an external cap for closing an upper end portion of the reservoir fill port; a pressure valve disposed in the reservoir fill port to allow the inside and the outside of the reservoir fill portion to fluidically-communicate with each other; a valve seal provided to allow the air to flow from the outside into the internal to the cooling system by being deformed when pressure in the internal to the cooling system is lower than a predetermined pressure; and a positive pressure spring elastically supporting the pressure valve such that the pressure valve closes the internal to the reservoir fill port.

A safety cap device for controlling a pressure in a radiator includes a valve seat provided with a valve receiving space in which a first communicating hole is formed. A negative pressure valve is provided movably in the first communicating hole. A seal is disposed on a receiving surface of the valve seat and disposed movably with the negative pressure valve. The seal has a second communicating hole formed at a central portion thereof. A positive pressure valve is disposed on the seal and has a third communicating hole formed at a central portion thereof. A cap covers an upper portion of the valve seat. A spring is interposed between the positive pressure valve and the cap. A fluid receiving part is in the valve seat to prevent cavitation caused when an internal fluid expands.