OPERATING PRINCIPLE

The valve is closed by the outlet pressure acting on the bottom of the diaphragm, thus compressing the spring when the pre-set value is exceeded. As long as there is "no-flow" (no water being drawn through the valve), the outlet pressure is kept constant at the pre-set value.
When water is drawn through the valve (when a tap is opened down-stream), the outlet pressure decreases and the spring pushes back the diaphragm. This opens the valve.
These valves have a unique "self-damping" effect when the valve is kept open during prolonged use. This means that there is no erratic opening of the valve, but a steady continuous flow.

OPEN POSITION

Pressure on the outlet side drops.The spring pushes against the diaphragm,and the valve-disc connected to it, thus opening the valve.

CLOSED POSITION

The outlet pressure rises.The spring is compressed by the diaphragm pushing against it.When it reaches the pre-set pressure the valve is closed by the valve-disc being lifted by the diaphragm thus preventing any further increase of pressure on the down-stream side.