holes on the lower side 6 b located in its middle part they are diametrically opposite one another in the form of embodiment shown in fig2 to 10 the needle has a conical section 6 c downstream of the orifices 6 b upstream of the orifices 6 b the needle has a first part 6 d with a cylindrical outer section and a second part 6 e with a conical outer section increasing towards the base of the needle originally the second part had a greater diameter than the first part so as to form a peripheral edge 6 f the resilient seal 5 is made of silicone and is in the form of a tube with an outer section that is conical in shape intended to extend into the chamber 3 from the body of the joint 2 up to the free end of the terminal compartment 3 c of the chamber 3 the seal 5 comprises a base portion 5 a a middle portion 5 b and an end portion 5 c the base portion 5 a of the resilient seal 5 is intended to rest on the body of the joint 2 in a non compressed position that is to say in the released position neither the base portion 5 a of the resilient seal 5 nor the central portion 5 b is in contact with the walls of the chamber 3 the inner wall of the middle portion 5 b of the resilient seal 5 comprises a peripheral pad 5 b 1 positioned so as to close the lower lateral holes 6 b of the needle when the seal is in the released.