Flow Control

Side-stream filters keep hydronic systems healthy like kidneys clean blood, yet almost nobody knows the actual flow rate through them. For consistent filtration regardless of variable pump head and filter loading, an automatic flow limiter in the side-stream circuit is the practical solution.

New automatic flow limiters were blamed when a heating coil produced no heat, but zero pressure drop across the limiter proved it wasn't plugged. The real culprit was a butterfly valve with a cleanly broken shaft — the handle moved but the disc didn't. Sometimes the simplest components fail in unexpected ways.

A domestic hot water recirculation pump showed almost no differential pressure — which actually meant too much flow, not too little. The cause: a metric conversion slip during submittals supplied 10 GPM flow limiters instead of 1.0 GPM, allowing the pump to drift nearly off its curve.