Backflow prevention is accomplished for this
older (wet-pipe) sprinkler system by means of a single flanged check
valve. Its design incorporates a counter-weight on the downstream side of
the clapper to hold the clapper with a tight seal in the closed position. The
cast iron body is painted red. Two tapped bosses permit by-pass meter
trimming.
Q: Do you have any friction loss data on older, single check valves? I can’t find much of anything. Our local building officials are having owners upgrade the headers to incorporate a backflow preventer. I don’t really think it’s fair to owners of buildings (that they have occupied for many years) to be required to upgrade their systems due to an added backflow preventer. Since many of the systems are pipe-scheduled and a lot of times they don’t work when calculations are performed, it requires time to figure out the new calculations and a lot of renovation.
A:Right, it’s no laughing matter. The whole mess would be a lot easier to stomach if the retrofitting of a backflow preventer on a fire sprinkler system amounted to any kind of real benefit. While NFPA 13 (2007) includes a retroactivity clause (1.4) that grandfathers in the older sprinkler systems, it also requires in duplicitous fashion that (8.17.4.6.2) “a thorough hydraulic analysis” be performed “when backflow prevention devices are to be retroactively installed on existing systems,” including as part of this exercise “all necessary system modifications to accommodate the additional friction loss.”
All of this nonsense and expense could easily be averted if the code simply permitted an additional flanged check valve to be added to the existing system. This would add up to two check valves - the same thing you’re accomplishing with the installation of a double-check backflow prevention device. However, since that exacting verbiage does not appear in NFPA 13, you are at the mercy of the legislation passed by your local water purveyors. And believe me, fire safety is not anywhere on their list of priorities.
The data you are looking for can be found on cut sheets in older manufacturers’ data books. The friction losses incurred through single, weighted check valves is small, as you might expect, and the numbers vary from model to model. With a flow of 500 gpm, the 4" Reliable D swing check valve loses 0.70 psi; the 4" Grinnell F520 swing check loses 1.60 psi; the 4" Globe B detector check loses 1.90 psi; and the 4" Ames detector check valve loses 2.36 psi.
Friction losses are similarly low when flowing 1,000 gpm: the 6" Viking C-2 swing check loses 0.39 psi, the 6" Central 90 swing check loses 1.00 psi; and the 6" Globe B detector check valve loses 1.50 psi.
Q: Our general contractor has proposed that a chain-link fence surround the area in a new warehouse that will contain an electric-driven fire pump and bypass, jockey pump, and controllers. The fire pump will be above grade level. Does code require that the pump be situated in a separate room protected in two-hour rated construction?
A.I have heard questions like this one many times. The answer to what the code actually requires lies in Chapter 5 of NFPA 20, “Standard for the Installation of Stationary Pumps for Fire Protection.” What is mandated, and brand new to the 2003 edition under paragraph 5.12.1.1, is that indoor fire pump units be physically separated or protected by fire-rated construction. Everyone is so accustomed to the old policy (no fire-rated construction needed) that the new requirement, in practice, is not frequently adhered to. But if the structure and the pump room itself is protected by fire sprinklers, then the required separation consists of one-hour fire-rated walls. Separating fire pumps from the rest of the building is done to provide protection against freezing, floods, fire, explosion, and so forth.
For years, the NFPA 20 appendix has included a sentence that reads “some locations or installations may not require a pump house.” Back in 1981, the NFPA issued a Formal Interpretation requiring that the fire pump and associated equipment be separated from the remainder of the building with minimum two-hour fire rated construction. Then, a 1983 Formal Interpretation stated that the fire pump and related equipment need not be separated from all other mechanical equipment and also that “It is not the intent of the Committee to recommend retroactivity of the (1981 Interp) two-hour construction standard unless the authority having jurisdiction determines that the continued use constitutes a distinct hazard to life or adjoining property.” However, any actual enforcement of these 1981 and 1983 interpretations seems to have somehow fallen by the wayside in recent years. Until the 2003 edition, the NFPA had no specific fire rating policy in this regard.
The real issue here is equipment protection. When an insurance company is highly involved and on their toes, I have a $100 bill in my pocket that says the fire pump will be housed in a separate, heated, non-combustible, sprinklered, and adequately ventilated fire pump room with proper floor drainage provided. This pump room should also be situated as closely as possible to areas where fire sprinkler protection is of the most critical concern. The intent is now clear that the fire pump, driver, and controller must be completely protected from mechanical damage originating from any potential adverse conditions, and physically located in their own designated fire pump room.
This below-grade room is dedicated solely to the
fire pump and bypass, jockey pump, controllers, and related fire sprinkler system
equipment. An engineer is perched directly in front of the fire pump
controller.
A.The appropriate NFPA pamphlet to reference is NFPA 13, and specifically, Chapter section 16.2.4.2.3. It reads, “the elevation of in-rack sprinkler deflectors with respect to storage shall not be a consideration in single- or double-row rack storage up to and including 20 ft. high.” Section C.16 notes that “in one 20-foot-high test, sprinklers were buried in the flue space 1 foot above the bottom of the pallet load, and results were satisfactory. Coverage of aisles by in-rack sprinklers is, therefore, not necessary, and distribution across the tops of pallet loads at any level is not necessary for the occupancy classes tested.”
Chapter 6 of the old NFPA 231-C pamphlet required that in-rack sprinklers be located in the racks at the level nearest one-half to two-thirds of the storage height for all overall rack storage heights of 25 feet or less. This requirement survives today under A.16.2.4.2.2 in the (2007 ed.) NFPA 13 Appendix, where other recommendations include placing in-rack sprinklers at least six inches above pallet loads, and “away from rack uprights.” In your case, even though the in-rack sprinkler elevation can be just about anywhere, it would be best to place them right smack in the middle of the storage arrangement, just beneath the second tier.
Q: If the automatic sprinkler system (250 gpm at 50 psi) of a combined standpipe system requires a fire pump, does the fire pump have to be sized for the standpipe demand (1,000 gpm at 135 psi) if the facility is not a high-rise building?
A.:When standpipes are a requirement, the general rule-of-thumb for Class I and Class III standpipes is 500 gpm for the first standpipe, and then 250 gpm each for the remaining number of standpipes, even in a completely sprinklered building. If the floor area is greater than 80,000 square feet, the second most remote standpipe must also accommodate 500 gpm. The total flow rate does not have to be more than 1,250 gpm. With combined systems, the sprinkler system demand is permitted to be satisfied by the standpipe system demand.
In some situations, it may be desired that 2-1/2 inch hose valves be installed within facilities in which these valves aren’t required by code or that may not require standpipes.
Section 8.17.5.2.1 in NFPA 13 states that “in buildings of light or ordinary hazard occupancy, 2-1/2 in. hose valves for fire department use shall be permitted to be attached to wet pipe sprinkler system risers.” The code goes on to say that, in such cases, a separate isolating control valve and a check valve should be included for the run off of the combined sprinkler system riser that supplies the fire sprinklers. Also, the minimum size of that riser must be 4” unless hydraulic calculations prove that a smaller riser can supply both the sprinkler demand and hose stream allowances at that juncture.
In order to avoid confusion with such an arrangement, it is advisable that this riser not be referred to as a standpipe per se. Using the term “fire protection riser” will serve not only to acknowledge the intent of Section 8.17.5.2 but also to avoid a proclamation by a misguided AHJ to adhere strictly to standpipe volume and pressure requirements, which are not really applicable in buildings where standpipes are not required by code.
