Sure, but why assume anything? Why not calculate it to the bottom of the tank? A flow test is: Static--- PSI/.433=h ft. pitot is velocity pressure/.433=h ft giving the water the velocity--- times the sq ft of the hydrant butt gives ft^3/sec-- (the .8 or .9 comes from the coefficient of constriction-- the diameter of the stream is less than the opening)-- this would be the diameter of the pipe at the bottom of the tank. The difference with a flow test is it is steady pressure (therefore steady flow)-- if the tank had steady fill rate with overflow 'drain', it would be the same thing, because h would be constant.
-----Original Message----- From: Ralphy Henderson [mailto:[email protected]] Sent: Tuesday, June 15, 2010 2:40 PM To: [email protected] Subject: RE: Gravity Tanks 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)
