Pete, Along the line of John's question, is the water in the suction tank potable? Or more importantly, does it need to be potable? If not, there is no need for a BFP between it and the pump. If the tank is filled via a potable water source, then the BFP could be installed at that connection point (and likely would be smaller). If that's physically possible, it would eliminate the potential issue you mention in 2.
Ed Kramer Littleton, CO > A consultant has shown a new double check valve backflow prevention > device to be installed in the suction side of a fire pump(s) system. > The fire pumps (horizontal split case) draw from a tank that is located > below the pump. It has been in service for many years without a > backflow preventer and without a problem. The requirement for a BFP is > evidently our own, though I haven't researched that as yet. > > NFPA 20 says > > 5.14.9* Devices in Suction Piping. > 5.14.9.1 No device or assembly, unless identified in 5.14.9.2, that > will stop, restrict the starting, or restrict the discharge of a fire > pump or pump driver shall be installed in the suction piping. > 5.14.9.2 The following devices shall be permitted in the suction piping > where the following requirements are met: > (1) Check valves and backflow prevention devices and assemblies > shall be permitted where required by other NFPA standards or the > authority having jurisdiction. > (2) Where the authority having jurisdiction requires positive > pressure to be maintained on the suction piping, a pressure-sensing line > for a low suction throttling valve, specifically listed for fire pump > service, shall be permitted to be connected to the suction piping. > (3) Devices shall be permitted to be installed in the suction supply > piping or stored water supply and arranged to activate a signal if the > pump suction pressure or water level falls below a predetermined > minimum. > (4) Suction strainers shall be permitted to be installed in the > suction piping where required by other sections of this standard. > (5) Other devices specifically permitted or required by this > standard shall be permitted. > > A.5.14.9 The term device as used in this subsection is intended to > include, but not be limited to, devices that sense suction pressure and > then restrict or stop the fire pump discharge. Due to the pressure > losses and the potential for interruption of the flow to the fire > protection systems, the use of backflow prevention devices is > discouraged in fire pump piping. Where required, however, the placement > of such a device on the discharge side of the pump is to ensure > acceptable flow characteristics to the pump suction. It is more > efficient to lose the pressure after the pump has boosted it, rather > than before the pump has boosted it. Where the backflow preventer is on > the discharge side of the pump and a jockey pump is installed, the > jockey pump discharge and sensing lines need to be located so that a > cross-connection is not created through the jockey pump. > > 1. Is there a problem with locating the BFP in the suction side and > what may that be? I don't really understand the statement "It is more > efficient to lose the pressure after the pump has boosted it, rather > than before the pump has boosted it. " > > 2. Has anyone looked into this type of situation where the BFP in the > suction side of the centrifugal pump actually created a problem > regarding the net positive suction head (NPSH) required for the pump? I > haven't done the calculation, but am curious if this is a deal breaker > for the possibility of placing the BFP in the suction when drawing water > from a tank with a centrifugal pump. > > 3. Why would a BFP be required for the fire service in the first place? > Would the fire pump test header (with hoses connected) be reason to > install a BFP on the suction side of the fire pump? > > 4. If I put the BFP on the discharge side, would the test header still > be a problem with respect to backflow? > > Thanks > > Pete > VA _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum To Unsubscribe, send an email to:[EMAIL PROTECTED] (Put the word unsubscribe in the subject field)
