The Pratissoli S4090 safety valve is a manually-adjustable, pressure- operated device which, according to its setting, releases the excess of water when the pressure inside the pump/system exceeds the adjusted value, thus reducing the pressure. The normal working conditions can be restored by turning off and then restarting the system.

The valve has been designed to protect positive-displacement pumps or components (such as containers and pipes) of high pressure water hydraulic systems up to category II.