guiding conduit 74 that communicates with a suction tube 75 and the needle valve 35 comprises an essentially cylindrical section that slides in the guiding conduit which is provided with a bottom shoulder 77 the needle valve 35 also comprises a shoulder 78 and the spring is mounted with initial pre compression between these two shoulders the end of the tubular neck 26 of the pump body comprises an annular groove that increases the flexibility of the peripheral lip 31 in watertight contact with the cylindrical inner wall of the inner element of the tappet button the longitudinal channel or channels 45 communicate with the dosage chamber at their ends when the tappet button is in the position referred to as loose the plug shaped part of the pump body 69 is inserted by force in the opening 19 of the reservoir this opening is surmounted by a thinner collar in which the cylindrical outer skirt of the tappet button is mounted the presence of a vent is not required if the reservoir is only partially filled the operation takes place as seen in the preceding description fig2 shows that the dosage chamber 27 is at its maximum volume and that the communication between this dosage chamber and the reservoir is not interrupted since the ends of the lateral longitudinal channels establish the communication between the reservoir 13 and the said dosage chamber conversely as soon as the tappet button is pressed fig3 this communication is interrupted since the needle valve 35 still in contact with the tappet button begins to enter the guiding.