Before microprocessors and digital control systems dominated boiler rooms, industrial automation relied on precise analog instruments like those pictured below from Republic Instruments and Controls of Chicago. Their line of mercury U-tube electrical flow meters, pressure/l­level gauges, CO₂ analyzers, and boiler meters helped operators monitor everything from steam and air flows to combustion efficiency, all without today’s electronics.

These analog instruments laid the groundwork for modern burner and control systems by turning physical data into actionable control signals. In fact, the legacy of measurement and control passed through several generations of companies: Republic Instruments later merged operations into Hays Republic Corporation, which in turn formed part of the product line consolidated under Hays Cleveland Controls in the mid-1990s, and Preferred Utilities acquired Hays Cleveland in 2025.

The principles Republic utilized such as, continuous monitoring, remote readout, integrator/recorder logic, live on today in systems like our PCC-IV multi-loop controller and BurnerMate Universal Control systems. What began as simple dials and tubes has evolved into real-time logic, analytics dashboards, and remote diagnostics, yet the mission remains the same: reliable control and actionable insight.

From mercury tubes to microprocessors, the path of combustion control development runs straight through history.

See the original Republic Flow Meters catalog below and follow our series celebrating the tools that built the industry we serve today.