Larry said it great. To add - if one of them is a redundant water supply, then your system should be designed to the lower if the two water supplies.
Sent from my iPhone > On Feb 19, 2015, at 6:11 PM, "Larry Keeping" <[email protected]> wrote: > > Each water supply is required to have a check valve. Initially, the water > from the tank, which is the higher pressure source, will provide the entire > supply because the lower pressure check valve remains closed. At the point > where the water supplies become about equal, the municipal supply will start > to contribute, but as the tank is depleted its pressure drops such that its > check valve shuts. Then the entire supply is from the municipal source. > > If a calculation program allows for multiple water supply sources, it > shouldn't be considered to be realistic, unless everything is equal (ie. two > identical fire pumps assemblies) because in reality one supply will have a > higher pressure than another, thus shutting its opposite CV. > > On the assumption that one supply will have higher pressure but lower volume > and the other has lower pressure with higher flows, two separate calculations > should be conducted, one for each water supply scenario. One with the tank at > its worst case/lowest water level and one for the municipal supply. > > The idea of having two water supplies is not to use them together, it is for > redundancy, in case one of the sources becomes unavailable. > > Larry Keeping > > > -----Original Message----- > From: Sprinklerforum [mailto:[email protected]] > On Behalf Of Paul Cetani > Sent: February-19-15 5:48 PM > To: [email protected] > Cc: [email protected] > Subject: RE: Hydraulic Calculations with two water sources > > Hi Mark, > The City water main is not gravity fed only the secondary supply is from a > gravity fed tank. There is an existing check valve at the City Main. > > Paul B. Cetani > Exec. Vice President > > Nor Cal Fire, Inc. > 16840 Joleen Way, Bldg A > Morgan Hill, CA 95037 > T 408-776-1580 > F 408-776-1590 > [email protected] > www.norcalfire.com > > CONFIDENTIALITY NOTICE: This message and any document accompanying it may > contain confidential information belonging to the sender. The information is > intended only for the use of individual or entity named above. If you are not > the intended recipient, or the employee or agent responsible to deliver this > message to the intended recipient, you are hereby notified that any > disclosure, copying or taking of any action in reliance on the contents of > this information is strictly prohibited. If you have received this > transmission in error, please immediately notify us by telephone to arrange > for return of the documents. > > > -----Original Message----- > From: Sprinklerforum [mailto:[email protected]] > On Behalf Of Mark A. Sornsin, P.E. > Sent: Thursday, February 19, 2015 2:20 PM > To: [email protected] > Cc: [email protected] > Subject: RE: Hydraulic Calculations with two water sources > > Paul - If I am reading this correctly, these are two gravity-fed systems. > One with a higher pressure head than the other. But in theory the higher > tank will simply drain until its elevation is equal to the lower tank. Or as > Charles illustrated, if you have a check valve separating the systems, the > higher system will be your source until it drains to the point that they are > at equal pressures. In the end, you will have a higher pressure with lower > volume; then when the pressures equalize, your volume will increase a little > but at the lower tank pressure. > > Mark A. Sornsin, P.E. | Karges-Faulconbridge, Inc. | Fire Protection > Engineer | Fargo, ND | direct: 701.552.9905 | mobile: 701.371.5759 | > http://www.kfiengineers.com > > -----Original Message----- > From: Sprinklerforum [mailto:[email protected]] > On Behalf Of Paul Cetani > Sent: Thursday, February 19, 2015 3:44 PM > To: [email protected] > Cc: [email protected] > Subject: Hydraulic Calculations with two water sources > > We have an existing fire service (from city water main) feeding hydrants and > sprinkler systems. The hydrant at the end of this fire service (hydrant #1) > has a static of 50psi, residual of 40psi, and a flow of 750gpm. > > Our client wants to add an additional water source, via a 200,000 gallon > water storage tank at 610 feet about the POC, hoping that the pressure will > increase. This storage tank also feeds existing hydrants. The closest > hydrant from this water source (hydrant #2) is 50 feet higher in elevation > than hydrant #1. Hydrant #2 has a static of 128psi, residual of 8psi, and a > flow of 265gpm. To connect the two water sources we are going to run a new > fire line 380 lineal feet from hydrant #1 to hydrant #2. We use HydraCalc > and it does not allow two separate water sources. > > Any suggestions on how to determine how much the pressure will be increased, > if any? > > Thanks, > > > > > > Paul B. Cetani > > <mailto:[email protected]> [email protected] > > > > CONFIDENTIALITY NOTICE: This message and any document accompanying it may > contain confidential information > > belonging to the sender. The information is intended only for the use of > individual or entity named above. If you are not the intended recipient, or > the employee or agent responsible to deliver this message to the intended > recipient, you are hereby notified that any disclosure, copying or taking of > any action in reliance on the contents of this information is strictly > prohibited. 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