Abstract: An opening/closing device 1 according to the present invention includes a gate 10 that receives a flow of a sewage W in an upright state, and can fall toward a downstream side of the flow and a first spring 52a that generates a force for bringing the gate 10 into an upright state, wherein the first spring 52 generates a force insufficient for bringing the gate 10 into the upright state if the gate 10 is in a fallen state, and generates a force sufficient for bringing the gate into the upright state if the gate 10 is tilted by an angle equal to or less than a predetermined angle.

Abstract: An opening/closing device includes a gate that receives a flow of a sewage, and can fall toward a downstream side of the flow, a fall prevention unit that prevents the gate from falling by supporting the gate, a support release unit that releases the support for the gate by the fall prevention unit, a first float that is arranged on the upstream side of the gate, and is smaller in specific gravity than the sewage, a surfacing prevention unit that prevents the first float from surfacing, a second float that is arranged on the upstream side of the gate, above the first float, and is smaller in specific gravity than the fluid, and a surfacing-prevention release unit that releases, resulting from surfacing of the second float, the prevention of the surfacing of the first float by the surfacing prevention unit. Further, the support release unit is activated resulting from surfacing of the first float.

Abstract: An opening/closing device includes a gate that receives a flow of a sewage, and can fall toward a downstream side of the flow, a fall prevention unit that prevents the gate from falling by supporting the gate, a support release unit that releases the support for the gate by the fall prevention unit, a first float that is arranged on the upstream side of the gate, and is smaller in specific gravity than the sewage, a surfacing prevention unit that prevents the first float from surfacing, a second float that is arranged on the upstream side of the gate, above the first float, and is smaller in specific gravity than the fluid, and a surfacing-prevention release unit that releases, resulting from surfacing of the second float, the prevention of the surfacing of the first float by the surfacing prevention unit. Further, the support release unit is activated resulting from surfacing of the first float.

Abstract: An opening/closing device 1 according to the present invention includes a gate 10 that receives a flow of a sewage W in an upright state, and can fall toward a downstream side of the flow and a first spring 52a that generates a force for bringing the gate 10 into an upright state, wherein the first spring 52 generates a force insufficient for bringing the gate 10 into the upright state if the gate 10 is in a fallen state, and generates a force sufficient for bringing the gate into the upright state if the gate 10 is tilted by an angle equal to or less than a predetermined angle.