When the pipe supplies water from the inlet end, because the needle valve , ball valve and float ball valve are normally open, water enters the water tank through the micro-filter, needle valve, control room, ball valve and float ball valve. At this time, there is no pressure in the control room; When the water level of the water tower rises to the set height, the ball float closes the ball float valve , controls the indoor water pressure rise, pushes the main valve to close and the water supply to stop. When the water level drops, the float controlled water valve reopens, the water pressure in the control room drops, and the main valve opens again to continue the water supply, keeping the setting height of the liquid level.