1. When the ram’s clack valve (B) is open, and check valve (C) is closed, water flows through the drive pipe (A) and out the clack valve chamber to the environment. The pressure of that flow causes the clack valve to rise up and block the flow. 2. Simultaneous to the clack valve closing, the water’s momentum forces the check valve (C) to open and pushes water into the pressure chamber, which contains a trapped volume of air (D). When water is forced into the chamber, a similar volume is displaced into the discharge line (E). 3. As soon as the water loses its momentum, the check valve (C) closes and the clack valve (B) drops open to begin the cycle once again. The compressed air pocket (D) keeps water flowing between cycles.
Illustration by Nate Skow