Joe, you continue to present input that takes this Forum up a significant notch- a beautiful combination of the theory then boiled down to the practical.
And so we don't get focused on simply avoiding cavitation, you remind us of the obvious- the pump not only has to not disintegrate, it needs to perform to spec. Thanks again for sharing- it is appreciated. George Church -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Joe Hankins Sent: Tuesday, November 04, 2008 10:56 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)
