I'm not sure I have anything to add, but this is a great anecdote. I've don't two flow tests in different parts of San Diego County (different water purveyors too) where the residual was HIGHER than the static because of pumps. And not variable speed, just stand back and watch in awe as the pressure fell 40-50% and suddenly came charging back to and beyond the static. One test was stupefying - the static was 95, which fell sharply to 75 and then surged up to 120. I was on the flowing hydrant and we had one 2.5" flowing straight across a six-lane arterial street (water department guy didn't trust my diffuser so he wanted to use his trusty pitot blade. We shut down and tried it with the 4" port but it nearly tore his hand off. Finally put my diffuser back on the 2.5" and got a clean pitot of nearly 100 PSI. Traffic was a mess, water everywhere, me laughing like a mental patient. It was awesome. Finally decided with the FD to go with 95 static and 90 residual at this ridiculous flow rate of 1700-something (ridiculous for a 2.5" port, I mean). Took 10% off and called it a day.
Steve Leyton Protection Design & Consulting San Diego, CA -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Thom McMahon Sent: Saturday, November 29, 2008 1:01 PM To: [email protected] Subject: RE: variable public water supply It sounds like more study for the actual system demand is required, otherwise your just guessing at the 15 vs. 20 flowing. You'll need to verify all start stop settings with the civil engineer for the water purveyor, and then look at the system demand, from the flow recorders. What time will the system supply/demand be the greatest? This is when your pump will kick in fastest. When is the supply/demand the lowest? This is when the pump will take longest to kick in, possibly even over the 660 Gpm your system demands if when you did your flow test the domestic demand on the system exceeded 160 Gpm, and your lowest demand is less than 10 Gpm, then it's possible your system will never kick the pump in. Thom McMahon, SET Firetech, Inc. 2560 Copper Ridge Dr P.O. Box 882136 Steamboat Springs, CO 80488 Tel: 970-879-7952 Fax: 970-879-7926 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Todd Williams Sent: Saturday, November 29, 2008 1:46 PM To: [email protected] Subject: RE: variable public water supply In this case, the new pump is variable speed and is designed to maintain a constant pressure. At the hydrant we were reading the pressures on, it kicked in at 45 psi and boosted it to maintain 65 psi out to the capacity of the pump. My thought is that ignoring the pump at sprinkler flows up to where the pump kicked in (approx 500 gpm in this case) is correct. If the system demand was over the 500 gpm, what would be the effectiveness of the sprinkler system at the flow goes from 0 to whatever the demand is when the curve is not 1.85 linear? From the time of first sprinkler opening, up to the 500 gpm, we will be operating on a different flow curve than what we will over the 500 gpm. Our designs are usually based on a maximum flow requirement only and assumes the linearity of the flow curve. Say you have a demand of .30/2000 (ignore hose streams in this case), or roughly 660 gpm. The sprinklers require 33gpm each. The design says that we have to calculate 20 sprinklers flowing. Should the design for the first 15 sprinklers (.30/1500) be based on the lesser curve and the .30/2000 be based on the curve with the pump? Two sets of calcs? How do you justify this to the septic system engineer that speced out the sprinkler system? _______________________________________________ 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) __________ Information from ESET NOD32 Antivirus, version of virus signature database 3650 (20081128) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com __________ Information from ESET NOD32 Antivirus, version of virus signature database 3650 (20081128) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com _______________________________________________ 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)
