Automatic shut off valves (ASOV) stop the flow of concentrate (often referred to as "waste water") when the flow of purified water is stopped (by a float valve, or by other means).  Comes with detailed instructions. Equipped with four quick-connect fittings for instant installation.

ASOV's work only when several other parts are present and working properly:

1. A float valve or other valve at the end of the purified water output line.  
2. A check valve (see fittings page) installed between the RO permeate (purified water) port and the auto shut off valve.

When pressure in the purified output tube reaches about 66% of the pressure in the system feedwater tube (standard ASOV), or about 85% in the case of the high pressure ASOV, the device will shut off the flow of feedwater to the RO membrane - and thereby stop the flow of concentrate.  The high pressure ASOV makes sense only in applications where the purified water is being delivered to a pressurized storage container - especially if a permeate pump is also installed.