What stops the flush cycle in a diaphragm flush valve?

The flush cycle in a diaphragm flush valve is controlled primarily by the force in the upper chamber of the valve. When a flush is initiated, water flows into the upper chamber, creating a pressure differential between the upper and lower chambers of the diaphragm. This pressure differential is what keeps the diaphragm in the open position during the flush cycle.

As the flush continues, the water level in the upper chamber equalizes with the lower chamber, leading to a decrease in pressure. Once the pressure equalizes to a certain point, the force in the upper chamber is no longer sufficient to keep the diaphragm open, thereby allowing the diaphragm to close and effectively stopping the flush cycle. This mechanism ensures that the flush is efficient and automatic, relying on the principles of hydraulics to control the operation of the flush valve.

In this context, while other options may relate to different plumbing mechanisms or controls, they do not specifically pertain to the diaphragm flush valve's operation in the same way that the force in the upper chamber does; thus, it is the key factor in stopping the flush cycle.