Piezoelectric pump casing and space arrangement

A pump device comprising:

• a piezoelectric pump including:
• a first casing member,
• a second casing member,
• a plate member having a base part, a vibration plate, a support part that connects the base part to the vibration plate, and a plurality of through holes defined by and adjacent to the base part, support part, and vibration plate, and
• a piezoelectric element disposed on the vibration plate,
• wherein the first casing member, second casing member, and plate member form a pump casing having:
• a lower wall that defines an inlet and an outer main surface of the pump casing,
• an upper wall that defines an outlet, and
• a side wall that extends between and connects the upper wall and lower wall, the side wall defining an external surface of the pump casing different from the outer main surface,
• wherein the vibration plate of the plate member is disposed inside the pump casing and divides an interior of the pump casing into a first portion on a side near the inlet and a second portion on a side near the outlet;
• and
• an outer casing providing a space allowing communication between an external inlet and the inlet of the pump casing, wherein the external inlet communicates with an outside,
• wherein a first main surface of the outer casing faces the outer main surface of the pump casing,
• wherein the space extends at least directly between the outer main surface of the pump casing and the first main surface of the outer casing, and
• wherein the space provides a path for fluid to flow in a direction from the external inlet of the outer casing toward the inlet of the pump casing, wherein the direction is parallel to the outer main surface of the pump casing,
• wherein the space extends directly between the external surface of the pump casing and a surface of the outer casing different from the first main surface.