The Evolution of Variable-Speed Fire Pump Technology
Variable-speed fire pump technology provides a reliable solution for managing system pressure. Introduced in 2003 with the first UL-listed electric controller and expanded in 2004 with diesel pressure-limiting devices (PLDs), these systems gained FM Global approval by 2008. Today, manufacturers like TornaTech, Firetrol, and Clarke offer FM-approved solutions that enhance design flexibility through active pressure management.
These systems work by adjusting the driver speed to maintain a set pressure. Electric controllers utilize variable-frequency drives (VFDs) to modulate motor speed, while diesel PLDs throttle the engine. To ensure safety, NFPA 20 (4.12.1.1) requires the automatic circulation relief valve to be set at least 5 psi below the operating pressure. In the event of a failure, an automatic bypass allows the driver to run at full speed, with a backup main relief valve preventing overpressure.
The Challenge of Overpressure
Booster pumps are often necessary to supplement city water supplies, but they can inadvertently create excessive pressure. Since city water pressure is highest at no-flow (static) conditions and pump boost is non-linear, total system pressure can easily exceed the 175-psi rating of standard sprinkler components. Elevation changes in multi-story buildings further compound this issue.
Historically, high pressures were managed with pressure-reducing valves (PRVs) or main relief valves. However, PRVs can be unreliable and are banned in some jurisdictions, while relief valves often waste thousands of gallons of water during testing. Variable-speed technology addresses these drawbacks by preventing overpressure at the source rather than just mitigating it after the fact.
Testing Requirements
Testing variable-speed systems is distinct because speed reduction alters the net pressure curve. NFPA 20 Chapter 14 requires acceptance testing in variable-speed mode at increments from no-flow to 150% of the rated load. Additionally, the pump must be tested at its rated speed for minimum, rated, and peak loads.
During annual flow tests, follow manufacturer-specific procedures. This may involve disabling pressure-limiting features to verify the unmanaged performance curve or using RPM correction formulas while the device is active. Per NFPA 25, if the water supply cannot reach 150% flow, testing should proceed to the greater of system demand or rated flow.
If your facility faces overpressure risks—whether due to high city pressure, elevation, or complex fire protection needs—a variable-speed pump may be the ideal choice.
Please contact Anvil Fire to determine if this technology is right for your facility.