Virtually all reverse osmosis systems have one of these shut-off valves.

Its purpose is to shut the system down when the tank is full, thereby saving water that would otherwise go to waste.

The F296 RO shut-off valve shuts off when the tank pressure is approximately 2/3rds line pressure.

It will replace most types.

This RO shut-off valve has 1/4 inch pushfit connections

This is a high quality component, not a cheap copy.