Hello all, We have recently relocated several BFPs from the discharge side of the pump to the suction side. I have not seen the requirement causing the systems that have been installed for 10+ years to require the change, But I was told it by the AHJ I was discussing this with "It has something to do with DEHC and too much standing water in the pipe leading to the pump and standing water in the pump casing". As a side we also talked about possible contamination from servicing the pump and pump bearing lubricants getting into the water.
Saturday, August 30, 2008, 8:25:09 AM, you wrote: > With respect to question 1, I believe it's due to the fact that the locating > the BFP on the suction side will have an impact on the available water > supply to the pump. Plot a curve of the water supply to the pump suction. > Now take that curve and reduce it due to the loss of the BFP. There is less > water available to the pump, which will cause an issue if its less than the > system demand. > Conversely, if the BFP is located on the discharge side of the pump you can > always increase the pump boost if necessary to overcome the BFP loss. All > of the water that was available to the pump suction is still available, > albeit with an increased boost necessary to utilize it. > Christopher Born, P.E. > Clark Nexsen, P.C. > Norfolk, VA > ----- Original Message ----- > From: "Larrimer, Peter A" <[EMAIL PROTECTED]> > To: <[email protected]> > Sent: Thursday, August 28, 2008 8:51 AM > Subject: Backflow preventer installation > Learned list serv members: > 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) > _______________________________________________ > Sprinklerforum mailing list > http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum > For Technical Assistance, send an email to: [EMAIL PROTECTED] > To Unsubscribe, send an email to:[EMAIL PROTECTED] > (Put the word unsubscribe in the subject field) -- Best regards, Charles Thurston Coastal Fire Protection Coastal mailto:[EMAIL PROTECTED] _______________________________________________ Sprinklerforum mailing list http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [EMAIL PROTECTED] To Unsubscribe, send an email to:[EMAIL PROTECTED] (Put the word unsubscribe in the subject field)
