Apparatus for applying a liquid in droplets to a surface

Claim 1

In an apparatus for applying a liquid in droplets to a surface, including an ejection head having means forming a pressure chamber in the ejection head, means forming a discharge channel in the ejection head, the discharge channel communicating with the pressure chamber, means forming an inlet channel in the ejection head, the inlet channel communicating with the pressure chamber, the apparatus further including a reservoir for the liquid, conduit means coupling the reservoir with the inlet channel for supplying the pressure chamber with liquid and a device connected to the ejection head for effecting momentary pressurizations of the liquid in the pressure chamber, shutoff means in the conduit means, the shutoff means having an open position for maintaining communication between the reservoir and the ejection head in the operating state of the apparatus, the shutoff means having a closed position for blocking communication between the reservoir and the ejection head in the non-operating state of the apparatus, the improvement comprising a pressure equalizing device including wall means bounding and defining a pressure equalizing chamber entirely filled with the liquid, said pressure equalizing chamber being in communication with said pressure chamber, at least one portion of said wall means being constituted by a first plate deformable for varying the volume of said pressure equalizing chamber, said first plate being attached to said ejection head and being responsive to the temperature of the liquid in said pressure chamber and in said pressure equalizing chamber; a second plate affixed rigidly face-to-face to said first plate; the material of said first plate having a coefficient of thermal expansion that is smaller than that of said second plate for increasing and, respectively, decreasing said volume upon expansion and, respectively, contraction of the liquid in said ejection head in said closed position of said shutoff means.