RO system help

[mark]

have a Aqua-safe unit and just took a look and there's a metal coupling between the housing and elbow (on the blue line side by where the arrow points to 4th stage membrane housing in the diagram), assume this is the check valve being mentioned?

[mike31154]

Dunno, but my check valve is hard to miss, after the elbow, plumbed into the blue line separately, before the four port auto shut off manifold. It has an arrow on it denoting flow direction.