PURPOSE: To reduce the influence of an external force due to the diaphragm by a diaphragm, by providing projections on the opposite side of the sealed side of an umbrella-shaped air valve, and placing the projections on the diaphragm to reduce the contact area of the valve.
CONSTITUTION: An umbrella-shaped air valve 13 for opening and closing the air suction hole 14 of a casing 9 is provided. Projections 15 are provided on the contact part with diaphragm, which is located opposite to the sealed side of the valve 13. The projections 15 extend radially from the center of the valve 13 and function to reduce the contact area of the valve and the diaphragm 11. Since the resistance to the contact is reduced by the projections 15, the valve 13 is made less likely to be affected by an external force exerted by the diaphragm 11.
KOJIMA KIYOICHI
MASUKO NORIO
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