I think Ralphy has it right. The empty tank level is the worst case pressure condition and in the big picture the falling tank head is nothing compared to 28 floors of head unless the tank height is a few sizes bigger than King Kong. A surprising calculation to make might be the tank stored gallons divided by the system gpm.
On Jun 15, 2010, at 2:40 PM, Ralphy Henderson wrote: > Couldn't you also do this: > > For assumption sake let's say 1st floor is light hazard and we're > anticipating we're going to need 400 gpm. Plot out the static > pressure of the tank (at the empty level) over zero gpm then > calculate our friction losses through the main from the water tank > down to the first floor based upon our anticipated 400 gpm and > subtract that from our static to get our residual pressure. Plot out > the residual pressure over 400 gpm and we now have a standard water > supply curve that can be used to determine other pressures at > available flows. > > --- On Tue, 6/15/10, Brad <[email protected]> wrote: > > From: Brad <[email protected]> > Subject: RE: Gravity Tanks > To: "'Matt Grise'" <[email protected]>, > [email protected] > Date: Tuesday, June 15, 2010, 5:44 PM > > For turbulent (sprinkler) flows, friction loss is proportional to > the square > of the velocity > > -----Original Message----- > From: Matt Grise [mailto:[email protected]] > Sent: Tuesday, June 15, 2010 12:41 PM > To: '[email protected]'; '[email protected]' > Subject: RE: Gravity Tanks > > Don't forget friction in the pipes! > > Matt Grisé PE*, LEED AP > Sales Engineer > Alliance Fire Protection > *Licensed in KS & MO > > 913.888.0647 ph > 913.888.0618 f > 913.927.0222 cell > www. AFPsprink.com > > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Brad > Sent: Tuesday, June 15, 2010 12:39 PM > To: [email protected]; [email protected] > Subject: RE: Gravity Tanks > > i.e., if the water level is 280 feet 'above your head', then h=280 > ft, v=134 > ft/sec (same as the Law of Falling Bodies- if you were dropped from > 280 ft, > you would be going 134 ft/sec when you hit the ground). > ft/sec*ft^2=ft^3/sec. If the flow is coming out of 4" pipe, ft^2=. > 09---- > *134= 12 * 7.48= 90---- * 60= 5400 GPM. As the level 'above your head' > drops, so does the velocity, so either use calculus, or call h the > bottom of > the tank, like I would have to do. It still seems like magic to me > that by > just using feet and seconds, given the rated psi and rpm ONLY, of a > fire > pump, I can calculate the diameter of the impeller (v=2*pi*r*f). It > seems > like magic bcoz for 15 years I tried to learn sprinkler calcs after > the PEs > had simplified it enough for me by factoring gravity out of the > formulas. > > -----Original Message----- > From: Brad [mailto:[email protected]] > Sent: Tuesday, June 15, 2010 8:30 AM > To: [email protected] > Subject: RE: Gravity Tanks > > mgh=.5mv^2 > m is the same on both sides so > v= sq root 2gh > h= v^2/2g > first thing is forget about gallons, minutes, and psi- use feet and > seconds: > ft, ft^2, ft^3, sec, sec^2. ft/sec=(ft^3/sec)/ft^2) > g=32.2 ft/sec^2 (if this project is on the earth). 7.48 gal/ft^3. > water > weighs 62.4 lbs/ft^3. > > -----Original Message----- > From: Todd Williams [mailto:[email protected]] > Sent: Tuesday, June 15, 2010 5:11 AM > To: [email protected] > Subject: Gravity Tanks > > Was there a thread on calculating flow from a gravity tanks a while > back? I couldn't find it. I have to do a calculation on the first > floor of a building fed from a gravity tank on the 28th floor > > Todd G. Williams, PE > Fire Protection Design/Consulting > Stonington, CT > 860.535.2080 > www.fpdc.com > > _______________________________________________ > Sprinklerforum mailing list > [email protected] > http://fireball.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 > [email protected] > http://fireball.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 > [email protected] > http://fireball.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 > [email protected] > http://fireball.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 > [email protected] > http://fireball.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 [email protected] http://fireball.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)
