The maximum sprinkler demand as per hydraulic calcs. is 222 gpm. The water supply is by means of storage tanks having a total volume of 7448 gallons. Just barely enough for approx. 33 minimute at maximum demand. The contractor has installed a 400 gpm fire pump. NFPA 20 requires gauge pressure at the fire pump suction flange to be 0 psi or higher when pump is operating at 150% of rated flow, which in this case is 600 gpm. Is this realistic? I know, if the suction pressure is 0 psi or higher for 600 gpm flow, it will work for all cases. However, I would expect a flow between the supply and demand with all design sprinklers flowing. Anyone with experience with pumps, care to comment?
Tony -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Joe Hankins Sent: November 4, 2008 8:56 AM To: [email protected] Subject: Re: Fire Pump Suction Boiling (cavitation) starts starts when the water pressure at the impeller is reduced to the vapor pressure of water at the water temperature. You see this addressed in the pump literature as "NPSH" The term net positive suction pressure (NPSH) is defined as the difference between the suction pressure and the vapor pressure of water and must be a positive number to avoid cavitation. At 68 degrees F water temperature, the vapor pressure is 0.35 psi. So, as long as the inlet pressure is greater than 0.35 psi absolute or -14.3 gauge, no cavitation. In practical terms, so long as the suction pressure is above -12 to -13 psi, you should be fine. When a typical centrifugal fire pump starts to cavitate, you'll know it. (sounds like the pump is full of rocks), and you're not going to damage the pump unless you let it cavitate for an extended period of time. The problem, of course, is that the pump performance deteriorates significantly. Joe _______________________________________________ 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) _______________________________________________ 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)
