Discharge valve apparatus, flush water tank apparatus, and flush toilet

A discharge valve apparatus attached to a reservoir tank in a reservoir tank apparatus for storing flush water, comprising:

• a valve body, attached to a top of a discharge opening provided in a bottom surface of the reservoir tank, for opening and closing the discharge opening by up and down movement thereof;
• a float, attached to the valve body, which drops in tandem with a drop in water level inside the reservoir tank;
• and
• a variable drop start timing mechanism to make a drop start timing of the valve body variable, the variable drop start timing mechanism being a buoyancy adjustment mechanism disposed on the float, the buoyancy adjustment mechanism including a reservoir portion, disposed on the float, for storing flush water, and an adjustment portion for adjusting a volume of the flush water stored in the reservoir portion, whereby a time over which the flush water is discharged from the discharge opening can be changed, and a volume of the flush water discharged from the discharge opening can be changed;
• wherein the reservoir portion of the variable drop start timing mechanism has a side wall erected on an outer perimeter side thereof, and the adjustment portion adjusts the flush water volume by changing a height of the side wall of the reservoir portion;
• and
• the reservoir portion adjustment portion of the variable drop start timing mechanism comprises differing channel portions at multiple height positions formed on the float or on the side wall of the reservoir portion, and a projecting portion capable of insertion in the channel portions provided on the side wall or float.