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Fire Pump Testing & RepairField's Fire Protection, Inc. Fire Pump Testing Trailer
Information provided from Fire Protection System Inspection, Testing, and Maintenance Third Edition Carson and Klinker A fire pump is designed to increase the water pressure. The pump intake discharge piping must be capable of flowing the required volume to which the pump will add the needed pressure for fire protection. The pump can be started manually, but is usually arranged to start automatically upon a drop in system pressure or the activation of a fire suppression system. Automatic starting requires a controller. Engines for operating the pump can be electric or diesel. Sizes range from 25 gallons per minute (gpm) to 5000 gpm.
Fire pumps are needed whenever pressure requirements of a fire protection system exceed the capabilities of the available water supply. Two types of pumps are typically used: centrifugal fire pumps, where water is available to supply the pump under pressure, such as a city supply; and vertical turbine pumps, where the available water supply is in a static state, such as a pond or reservoir. Water enters the centrifugal pump through the suction inlet and passes to the center of an impeller. Rotation of the impeller drives the water by centrifugal force to the rim, where it discharges. One of the unique features of a centrifugal pump is that it takes advantage of the inlet water pressure and adds the pump pressure to it. For example, a centrifugal pump with a rated pressure of 100 psi at a certain flow having a 25 psi inlet pressure will produce that flow at 125 psi.
A vertical turbine pump usually has a right-angle gear drive with impellers connected to the pump head by a vertical shaft. As the pump operates, the water is passed from one impeller to the next impeller, gaining additional pressure at each subsequent impeller until the water passes through the pump outlet. The number of impellers indicates the number of stages for the pump.
Fire pumps are rated by their ability to pump a specific volume of water, usually measured in gallons per minute or liters per minute at a rated pump pressure and pump speed. The pump must be able to deliver 150% of this rated flow at 65% of its rated pressure. In addition, under no-flow conditions, the pressure must reach not more than 140% of the rated pressure (sometimes called the churn pressure). Most centrifugal pumps have a single impeller and are known as single-stage pumps. For high pressure demands, multistage pumps are needed. Pumps are started and stopped by controllers. They start the pump when they sense the need for additional pressure or upon activation of a fire-extinguishing system. The controller can be arranged to stop the pump after reaching both a preset pressure and preset time. Pumps have timers so they will not continuously start and quickly stop, as would happen for a small leak or small flow. For the same reason, a small low-volume pump, known as a jockey pump, is often installed in the piping parallel to the fire pump to prevent cycling of the fire pump due to leaks.
Pumps are provided with circulation relief valves, to discharge water when the pump is being run with no water discharge. This valve is provided because, without it, the temperature of the water trapped in the pump casing would increase due to the centrifugal force created by the pump. The higher temperature could damage the fire pump. Pumps taking suction from ponds or wet pits are provided with screens to make sure that the pump is not damaged by the introduction of solid materials into the pump. Foot valves are also provided on suction lines to assure that the pump maintains its “prime.” (Centrifugal pumps need the inlet piping and the pump casing full of water in order to start pumping. This water is called the “priming water” or “prime”). Where variable-speed drivers are used (e.g., engine-driven pumps), pressure-relief valves are required. The relief valve will open should pressures exceed the system design pressure due to engine overspeed. Pressure-relief valves are also needed when the pump discharge pressure can exceed the rated pressure of any piping or valves on the discharge side of the pump. Fire Pump Testing and Maintenance Frequency Per NFPA 25, 2002
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