One way to mitigate this is to have multiple smaller valves that operate sequentially. In other words, you can use maybe a 2-1/2” valve and a 4” valve to replace a single 4” valve (for example). You set the smaller valve to open at 90% full and the 4” valve to open at 80% (I’m just pulling random numbers). That way, under normal fill conditions you just have the small valve open to refill the tank. But in a fire scenario when the level drops faster than the smaller valve can keep up with, then the bigger valve opens.
To answer the original question: Yes, you can reduce the tank size based on being able to refill it, but as Craig mentioned, there are some caveats. I assume the tank is a break tank feeding a fire pump, but does that fire pump feed only sprinkler systems? Does it feed a standpipe with hose valves? Does it feed hydrants on site? Would whatever you are protecting normally require any redundancy, or is the tank being provided solely because the available water supply is insufficient? -Kyle M From: Sprinklerforum [mailto:[email protected]] On Behalf Of Kenneth Berman Sent: Wednesday, June 13, 2018 2:14 PM To: [email protected] Subject: Re: [EXTERNAL] Ground Storage tank When I do inspections in the "country", and there's a storage tank with altitude valve, control valves are often partially closed to throttle the flow. When the 4" valve opens to fill the tank, it drops the pressure so much there's no water for toilets and sinks. Building owners, or occupants, "fix" the pressure problem long after the initial construction and acceptance tests. I can't count on the water main to resupply during demand. On Wed, Jun 13, 2018 at 1:41 PM, Prahl, Craig/GVL <[email protected]<mailto:[email protected]>> wrote: When sizing a water storage tank for fire protection do no forget the IFC code requirement for Fire Flow in section 507. It's an additional water supply requirement apart from sprinkler flow. This is especially critical if the municipal supply is not sufficient to meet the required flow rates as dictated by the Approved Method for determining Fire Flow. But to your question. It sounds like you want to take credit for the incoming water supply flow rate to reduce your storage capacity, correct? If that is the case, there are a few things that you must consider and you must get approval from the AHJ and any insurer. 1. Is the municipal flow rate guaranteed to be available 24/7/365? 2. Will the local Fire Code official and the owner's insurer approve of the concept. In theory you could take the credit and use the municipal supply as a buffer against the increased tank size but at some point in time you reach a point where you could consume at a rate greater than can be made up especially with the fire flow demand rate. We've only been successful in incorporating this concept on one occasion. Typically, our projects tend to be high value and high hazard and the lack of an adequate water supply for fire suppression and firefighting is not something that the AHJs or Insurers were willing to compromise on. But when the owner asks, we'll oblige and ask the question of the AHJ. Craig Prahl | Jacobs | Group Lead – Fire Protection | 864.676.5252 | [email protected]<mailto:[email protected]> | www.jacobs.com<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.jacobs.com&d=DwMFaQ&c=wn3mZQLIuInh2ClcJ0_DIA&r=Z_2A85VL7AQzoqudh6uOyS3bn8etxB7nLN8OBJwQd9A&m=qQd135zn_TMkTxYr5FwwmCd5uxlVCrSzB9-BXIYyT5Q&s=dbBIHoPyHME8yMsElaCwcYwl_XEFzKQ0dpBtYLiNMkI&e=> -----Original Message----- From: Sprinklerforum [mailto:[email protected]<mailto:[email protected]>] On Behalf Of George W. Henderson Sent: Wednesday, June 13, 2018 2:29 PM To: [email protected]<mailto:[email protected]> Subject: [EXTERNAL] Ground Storage tank I am attempting my first participation. We have the need for a ground storage tank. The MUD cannot supply volume or pressure. We size the tank to satisfy the code water supply duration. This tank about 200,000 gallons, Is it allowed to use the the MUD water supply refill to reduce the size of the tank? -- George W. 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