First of all, the pressure is different:
1. The pressure reducing valve keeps the outlet pressure unchanged.
2. The overflow valve keeps the pressure at the entrance unchanged.
Second, the export is different:
1. When it doesn't work, the inlet and outlet of the pressure reducing valve communicate with each other.
2, when not working, the overflow valve import and export impassability.
Scientific principles:
The pressure reducing valve is a valve that reduces the inlet pressure to the required outlet pressure by adjustment, and automatically keeps the outlet pressure stable by the energy of the medium itself.
From the point of view of fluid mechanics, the pressure reducing valve is a kind of throttling element with variable local resistance, that is, the flow and kinetic energy of fluid are changed by changing the throttling area, thus producing different pressure losses.