The working principle of a pressure reducing valve can be simply understood as inlet pressure+outlet pressure=spring force. The pressure at the outlet is controlled by controlling the opening of the shut-off port inside the pressure reducing valve. The smaller the opening, the smaller the liquid resistance of the shut-off port, the smaller the pressure loss, and the higher the outlet pressure. Conversely, the smaller the opening, the lower the outlet pressure.
Assuming the spring force acting on the diaphragm is F
The outlet pressure acting under the pressure reducing valve diaphragm is F1, the inlet pressure is P1, and the acting area of the diaphragm is S1 F1=P1 × S1
The inlet pressure acting under the pressure reducing valve spool is F2, and the outlet pressure is P2. The acting area of the spool is S2, F2=P2 × S2
When equilibrium is reached, F=F1+F2=P1 × S1+P2 × S2
When the pressure at the inlet fluctuates, assuming that the inlet pressure increases to P2+△ P and other conditions remain unchanged, the spring force F<F1+F2, the pressure under the diaphragm pushes the diaphragm upward, and the spring is compressed by F to increase. At the same time, the opening of the cutoff port decreases, the liquid resistance increases, the outlet pressure decreases, and F2 decreases, until a new equilibrium is reached.
When no one is using water at the outlet of the pressure reducing valve or the downstream of the valve is closed, the outlet pressure continues to increase, F2 continues to increase, and the pressure under the diaphragm pushes the diaphragm to move upward until the pressure reducing valve is closed. At this time, the outlet pressure of the pressure reducing valve is greater than the set value, but due to inertia, the upward moving diaphragm will not stop immediately, but will continue to move upward a little, which is equivalent to the valve chamber at the outlet becoming larger, the volume increasing, and the pressure of the internal liquid decreasing until it is exactly equal to the set pressure value at the outlet of the pressure reducing valve