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. 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