Check valve structure

1. A check valve structure comprising:

an inflow path and an outflow path for a fluid;

a valve casing communicating the inflow path with the outflow path; and

a valve element disposed in the valve casing and composed of an elastic material, the valve element including (i) a thin portion having a substantially circular shape in a plan view, the thin portion having a first surface positioned at an outflow path side and a second surface positioned at an inflow path side, and (ii) a thick portion protruding from a center of the first surface of the thin portion, wherein:

the valve casing includes:

a valve element support portion shaving an annular bottom portion configured to support an outer edge of a bottom surface of the thick portion without obstructing a fluid flow at a radial center of the annular bottom portion, and a peripheral wall portion extending from an outer peripheral edge of the annular bottom portion; and

a valve seat portion having a valve element contact portion configured to contact with a contact region of an outer peripheral edge portion on the second surface of the thin portion, and a valve seat surface disposed between the valve element contact portion and an outlet end of the inflow path, the valve seat surface being configured to contact the second surface of the thin portion inside of the contact region of the outer peripheral edge portion,

a hole portion extends from the radial center of the annular bottom portion to the outflow path, and

under a pressure of the fluid flowing from the inflow path to the outflow path, the contact region of the outer peripheral edge portion deforms elastically so as to separate from the check valve structure element contact portion and open the valve.

2. The check valve structure according to claim 1 , wherein a thickness of the thin portion at the contact region of the outer peripheral edge portion is 0.1 mm to 1.0 mm.

3. The check valve structure according to claim 1 , wherein, when the valve element is centered in the annular bottom portion, a distance between a side wall of the thick portion and the peripheral wall portion of the valve element support portion is less than a distance between the valve element contact portion and an end portion of the outer peripheral edge portion of the thin portion.

4. The check valve structure according to claim 1 , wherein the valve element has a protruding portion protruding from a center of the second surface, the protruding portion being configured to be inserted and removed from the inflow path.

5. The check valve structure according to claim 1 , wherein in a cross-sectional view of the check valve structure, a distance between a top portion of the peripheral wall portion of the valve element support portion and the outlet end of the inflow path in a cross-sectional view of the valve casing is less than a thickness of the center of the valve element from the bottom surface of the thick portion to the second surface.

6. The check valve structure according to claim 1 , further comprising:

an inclined surface extending outwardly from a top portion of the peripheral wall portion of the valve element support portion, and

recessed groove portions forming a plurality of flow paths directed toward the outflow path, the recessed groove portions being formed radially around the hole portion of the annular bottom portion and on the inclined surface.

7. The check valve structure according to claim 1 , wherein the valve casing is formed by fitting a first valve casing having the inflow path with a second valve casing having the outflow path.

8. The check valve structure according to claim 1 , wherein an outer peripheral edge of the thin portion is thicker than remaining portions of the thin portion.