Chris, As illustration: I don't know if this has been changed but the now Nordstrom, Downtown Seattle store has (had at least as recently as the changeover from Frederick & Nelson in the 90s) a diesel and an electric pump in a basement at essentially the level of the city feed. The city feeds both pumps through the same pipe but the diesel is checked against feeding back to the electric with both feeding the combination riser. (This isn't too important for this email but critical to the weird design.) The level below has a 65K gallon tank. The suction side of the diesel is in this tank with a homemade foot valve arrangement consisting of a very light horizontal swing check at the bottom of the tank. Directly above the pump is a 200 gallon tank with a float valve that operates a small positive displacement pump that keeps the small tank full. The small tank has drip lines that run down to the lantern ring coolant inlets on the pump and thereby keeps the pump casing and suction line full as water drips from the packing. Rube Goldberg but....
On Mon, Aug 4, 2008 at 7:10 AM, Chris Cahill <[EMAIL PROTECTED]> wrote: > Check out NFPA 20 - 5.14.3.2, allows -3 psi. So with 315' of 8" you're about > -1.7psi with 8" and with 6" about -6.6psi. So 8" is reasonable with no lift > or elevation on the tank. 6" would need elevation. > > 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. > > This is why fire trucks can draft out of a pond without parking in the pond. > The key is to not let air in. This is the reason for the vortex plate to > break up the drain vortex (swirl you see that sucks in air when you drain a > tub) from allowing air in before the actual water elevation reaches the > inlet elevation. > > While we follow the code it is very conservative in this area. Remember all > code limits are based on 150%. As long as you start with no air in the > suction line, and don't allow air in (through either slow draft or vortex > plates) a centrifugal pump will draft just fine. > > Chris Cahill, P.E. > Fire Protection Engineer > Sentry Fire Protection, Inc. > > 763-658-4483 > 763-658-4921 fax > > Email: [EMAIL PROTECTED] > > Mail: P.O. Box 69 > Waverly, MN 55390 > > Location: 4439 Hwy 12 SW > Waverly, MN 55390 > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Todd Williams > - FPDC > Sent: Sunday, August 03, 2008 7:07 AM > To: [email protected] > Subject: RE: effective tank volume > > The other detail is that I have to give them an elevation for the > bottom of the tank. In addition, there is about 315 equivalent feet > of pipe from the tank to the pump. the building requires a 500 gpm > pump and I plan on calling for an 8" suction line. I was also > thinking about insisting that the center line of the suction line be > 6 ft above the centerline of the pump for just that reason. > > > At 11:56 PM 8/2/2008, you wrote: >>Yes - but remember that you have positive pressure when the tank is >>filled. (Normally, a horizontal, split-case pump is taking suction >>from a tank whose water elevation - when filled - is above the >>centerline of the pump). 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. >> >>Mark Sornsin, PE >>Ulteig engineers, Inc. >>Fargo, ND >> >>-----Original Message----- >>From: [EMAIL PROTECTED] >>[mailto:[EMAIL PROTECTED] On Behalf Of Russell >>Sent: Friday, August 01, 2008 3:57 PM >>To: [email protected] >>Subject: RE: effective tank volume >> >>Would not anything below the centerline of the pump impellor be a negative >>pressure? Split-case centrifugal pumps have to have a positive pressure on >>the suction side. Or have I misunderstood the situation? >> >>Russell Rewis >>Brown Automatic Sprinklers, Inc. >>107C Hemlock Street >>Valdosta, Georgia 31601 >>229-244-8130 >>[EMAIL PROTECTED] >>-----Original Message----- >>From: [EMAIL PROTECTED] >>[mailto:[EMAIL PROTECTED] On Behalf Of Ed Kramer >>Sent: Friday, August 01, 2008 2:14 PM >>To: [email protected] >>Subject: RE: effective tank volume >> >>I recently completed a similar project. I agree with Mark, the available >>water is that part of the tank below the inlet of the overflow and above > the >>bottom of the vortex plate. Also, reference NFPA 22 section 4.1.3 (03 >>edition). >> >>Ed Kramer >>Littleton, CO >> >> > -----Original Message----- >> > From: [EMAIL PROTECTED] [mailto:sprinklerforum- >> > [EMAIL PROTECTED] On Behalf Of Todd Williams - FPDC >> > Sent: Friday, August 01, 2008 7:05 AM >> > To: [email protected] >> > Subject: effective tank volume >> > >> > I am working on a project where the water supply for the facility >> > will be fed from concrete tank(s). The absolute volume (completely >> > full) of the tank is 10098 gallons. A 6" suction line with elbow & >> > anti-vortex plate will need to be installed. According to NFPA 22, >> > the face of the suction elbow has to be a minimum of 6" above the >> > bottom of the tank. The take-out for the elbow is 8" and the top of >> > the pipe will be 4" (+/-) above that. I am trying to calculate the >> > effective or usable volume in the tank based on what my minimum >> > height above the floor can be relied on for suction. Would it be the >> > 6" to the bottom of the elbow? 14" to the center line of the suction >> > pipe? 18" to the top of the suction pipe? The tank is 10 feet tall, >> > so this could have a significant impact on available water. (BTW, I >> > am already assuming that the tank will only be filled 9" to 12" from >> > the top; would that be reasonable?) >> > >> > Todd G. Williams, PE >> > Fire Protection Design/Consulting >> > Stonington, Connecticut >> > www.fpdc.com >> > 860.535.2080 >> > _______________________________________________ >> > Sprinklerforum mailing list >> > [email protected] >> > http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum >> > >> > To Unsubscribe, send an email to:Sprinklerforum- >> > [EMAIL PROTECTED] >> > (Put the word unsubscribe in the subject field) >> >>_______________________________________________ >>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) >> >>No virus found in this incoming message. >>Checked by AVG - http://www.avg.com >>Version: 8.0.138 / Virus Database: 270.5.10/1585 - Release Date: 8/1/2008 >>6:39 AM >> >> >>_______________________________________________ >>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 >>[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) > > Todd G. Williams, PE > Fire Protection Design/Consulting > Stonington, Connecticut > www.fpdc.com > 860.535.2080 > _______________________________________________ > 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 > [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) > -- Ron Greenman at home.... _______________________________________________ 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)
