Variable speed fire pump controller  A Variable Speed (VFD) Fire Pump Controller is a fire pump controller that is able to vary the speed of the motor depending on the demand of the fire pump, resulting in the ability to hold a constant discharge pressure. It differs from other industrial variable speed control devices because it is now considered a life safety device, and so must adhere to the more rigid standards set forth by NFPA-20. Variable Speed Fire Pump Controllers were invented and released with a UL Listing for fire pump service in 2003 by Master Control Systems, Inc. Paragraph 10.5.5 in the 2003 edition of NFPA-20 recognized Variable Speed as an accepted method for operating the fire pump. Then in the NFPA-20 2007 edition, section 10.10 was added to clarify and enhance the previous standards. In addition to reading these standards, a detailed summary of them by James S. Nasby of Columbia Engineering can be found on slides 7–11. In 2008 Master Control Systems, Inc. became the first company to provide FM Approval for the controller. A full list of companies with FM Approval may be found here. Variable Speed Fire Pump Controllers are now accepted by NFPA-20, Underwriters Laboratories (UL), and most recently Factory Mutual (FM) for fire pump applications. Since the output pressure of a centrifugal pump varies with the square of the speed, pressure can be controlled accurately by controlling the speed of the pump. For example: a pump runs at 1785 RPM during shutoff with an output pressure of 204 PSI and a suction pressure of 0 PSI. If the speed of the motor is reduced by 10% to 1607 RPM, the new output pressure becomes 165 PSI. This in turn enables the Variable Speed Controller to maintain a perfectly flat pump discharge curve until the full rating of the pump is reached. Further, the variable speed controller adjusts for varying suction pressure – as in the following example: a city water supply of 65 PSI drops to 26 PSI while flowing. The variable speed drive will speed up to adjust for the sudden drop in pressure and slow down again when it is not needed – all the while maintaining a constant total discharge pressure. Variable speed technology is most often used to solve the following pressure issue situations: