Yes. Siphon - bad choice of word. Type too fast. "Negative pressure draft" - better.
Tarzan, PE -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Chris Cahill Sent: Monday, August 04, 2008 9:10 AM To: [email protected] Subject: RE: effective tank volume ...Also a clarification on what Mark said. "It is only after the tank has nearly emptied that you'd have a negative pressure condition. At that point, you'll be in a siphon condition." Some negative pressure is allowed. But also consider you have much bigger problems than air if the tank has run nearly empty during a fire. You have at least 30 minute but in reality 60 minutes or more. If you drain the tank I'd bet the fire overwhelmed the sprinklers in the first place and the FD didn't supplement and FD didn't put the fire out. 15 minutes is probably all that is needed in MOST (but not all) situations. True a centrifugal pump won't pump air. You need to start without air in the line, thus the equipment for positive head to start. And the pump doesn't siphon until air is drawn in. Perhaps he meant something else by siphon? Siphoning doesn't start just because you have negative suction pressure. You can draft well below the pump inlet. The theoretical maximum below the pump is the atmospheric pressure converted to feet. Twenty something feet of lift is certainly within reality. Yes you lose pressure on the discharge side by being negative. But again if you get near the bottom of the tank you have bigger problems.... Chris Cahill, P.E. _______________________________________________ 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)
