To provide a technology for accurately adjusting high back pressure required in an ink tank, and hardly controlled in a method using the weight of a valve body or the resilience of a valve spring.
A valve seat plate 60 is provided with an air hole 62 for connecting a first internal space 41a connected to an ink tank, and a second internal space 41b connected to the atmosphere. A length from the periphery 55 of the valve body 51 to a pooling portion 53 is less than the plate thickness between a holding portion 66 and a valve seat portion 65. With a shaft portion 52 extended, the pooling portion 53 comes into contact with the holding portion 66 and the periphery 55 comes into close contact with the valve seat portion 65 in a ring shape, to shut off the first and second internal spaces 41a and 41b. When pressure in the second internal space is more than pressure in the first internal space by a first pressure or more, the periphery 55 separates from the valve seat portion 65 to connect the first and second internal spaces. The thickness of a spacer 67 between the first and second plates 61a and 61b, constitute a part of the plate thickness.
MURATA MASAAKI
YAHAGI MITSURU
Hideki Abe