Thank you Rahe. Following a large number of tests, I realized that I have to expect a loss of about 40% across service connections from the Public Supply to the inside Riser.
It includes the losses due to the valves, strainer, backflow-preventer and water meter. This loss is substantially higher than the calculated loss. Together with a colleague from the fire department we initiated a motion to demand the installation of hydrant or any other testing outlet next to the riser to prove that the riser has sufficient water supply. This must be done by actual testing. The fire department accepted the motion. The old pipe problem I raised is also based on actual testing. I found that capacity of old pipes some location I tested is down to 25% of the calculated one. This is due to the same tuberculation you mentioned. What initiated my approach to the forum was a Telephone call I got from a Swiss Re-Insurer enquiring about actual testing, whether or not it is required by the NFPA. Dan Dan Arbel Tel: 972-4-8243337 Fax: 972-4-8243278 M: 972-52-2810593 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Monday, February 18, 2008 5:22 PM To: sprinklerforum@firesprinkler.org Subject: RE: C-Factor for old piping Dan, It is unfortunate that some will simply cuddle up to the familiar regardless of the possible consequences. I, personally, have a problem using a formula or equation that I don't fully understand simply because everyone else does. Some of this is very slowly creeping into the standards. For example, it has been noticed for some time that the Hazen-Williams equation does not work on high pressure mist systems. Now, NFPA 13 has a requirement to calculate anti-freeze systems with the Darcy-Weisbach formula. A large part of the problem is that NFPA 13 sets out the Hazen-Williams equation as the end all be all for sprinkler hydraulic calculations. All of the manufacturers of sprinkler hydraulic calculation software are, of course, on the same bandwagon. While it is true that the Hazen-Williams formula is much easier to use and that NFPA 13 allows one C-factor to be applied to all of the piping, depending on type and if wet or dry, it is really not that accurate. I hear a lot of folks say that it is conservative or that it has conservatism built into it but no one is able to tell me exactly where that conservatism is. So again, since NFPA 13 promotes only changing the C-factor we have to guess what that C-factor is if the conditions are beyond the scope of NFPA 13. Since NFPA 13 deals with only new pipe, then any application to old existing pipe is outside of the scope of NFPA 13. Therefore, the reality is that we may need to change not only the C-factor but exponents as well. For example, as pipe becomes rougher the exponent goes toward 2 versus 1.85. Hazen and Williams recognized this and brought it out in their work as the exponent going from 0.54 (reciprocal of 1.85) to 0.50 as pipe became rougher. They also indicated that the C-factor would change as well. The numerous variances that you can have with old pipe led them to simply try to provide a formula for the AVERAGE losses that would occur in new pipe made from different materials. So there we are, simply trying to come up with a C-factor that we think is applicable to predict the losses in a pipe that is old but the roughness is unknown. To be fair, it can be difficult to determine the friction factor in the Darcy-Weisbach equation without some physical investigation. However, once that investigation is undertaken, you know exactly how to apply the Darcy-Weisbach equation but you would still not know how to precisely apply the Hazen-Williams equation. As a real world example, I have an old building in New Orleans with a 20 year old sprinkler system that was supposed to be replaced entirely but, due to arguments by the contractor to reuse pipe, I agreed to have all pipe smaller than 3 inch replaced so that the contractor can reuse the mains. A well known FPE firm took some samples from the building that were suspicious for reuse owing to their condition. Most of them were not severe but bad enough that it led me to believe that there was worse in the building. Their samples of the large pipe looked better, hence my first inclination to reuse them. Later I had some of the mains on the floors opened and examined. These were severely tuberculated and much worse than the original samples. Since the contractor had already been allowed to reuse these mains, we had to decide what to do at this point. Through nothing more than a consensus opinion between myself, the contractor, and a third party, we decided to use a C-factor of 80 for all of the reused pipe. There was no more of an engineering basis than this and looking at a table of C-factors provided by a website. As you can see, since we could not investigate this condition further by test, we simply made an assumption and the contractor proceeded to prepare his hydraulic calculations from there. Without testing, we would have had to investigate every piece of pipe in the building and attempt to measure the height of the tubercules to use in a Darcy-Weisbach calculation. As an aside, when a hydraulic calculation uses a C-factor less than 120, the friction loss goes up but the equivalent length of fittings goes down. Also when the temperature goes from the minimum of 40 degrees F to 100 degrees F in a heated attic system, with all other things equal, the C-factor will change by 7 points. Thank You Rahe Loftin, P.E. Region 7 - GSA Office - 817-978-7299 Fax - 817-978-8644 Cell - 817-371-3102 "danarbel" <[EMAIL PROTECTED] To .com> sprinklerforum@firesprinkler.org Sent by: cc sprinklerforum-bo [EMAIL PROTECTED] Subject er.org RE: C-Factor for old piping 02/18/2008 02:06 AM Please respond to [EMAIL PROTECTED] resprinkler.org Thank you for your response. Your first phrase "Flow through the pipe and accurate measurement of the loss is the only way to understand what you have to work with" correlate with my massages. However it appears that the NFPA and many practitioners (as reflected by the responses I got) are comfortable with the Formula. No body came forward with actual field experience that supports the necessity to ascertain that what you actually get is what you designed for. Dan Dan Arbel Tel: 972-4-8243337 Fax: 972-4-8243278 M: 972-52-2810593 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Sunday, February 17, 2008 10:48 PM To: sprinklerforum@firesprinkler.org Subject: Re: C-Factor for old piping Dan, Flow through the pipe and accurate measurement of the loss is the only way to understand what you have to work with. Adjusting the C factor to compensate for aging is definitely a guessing process. You may look at tables that attempt to predict the C of older rough pipes but I would be suspicious of the information without some backup. At best this information would be an average of many tested samples. This still does not predict your specific losses. Please the see the following information concerning the Hazen-Williams equation and the C factor. The Hazen-Williams equation is used widely in water supply and sanitary engineering and almost exclusively in fire protection sprinkler systems. This equation uses a constant, the Hazen-Williams C, to indicate the roughness of a pipe interior. Because of the empirical nature of the equation, its range of applicability is limited. Many textbooks and software manuals give C values based on pipe type, condition, and age but do not give the range of applicability. Historic experimental data has demonstrated that C is a function of Reynolds number, relative roughness (absolute roughness divided by the pipe diameter) and pipe size. The Hazen-Williams equation is not dimensionally homogeneous and has narrow applicable ranges for Reynolds numbers and pipe sizes. The level of error when the Hazen-Williams equation is used outside its data ranges can be significant. The original work performed by Allen Hazen and Gardner Williams in their book “Hydraulic Tables – The Elements of Gagings and the Friction of Water Flowing in Pipes, Aqueducts, Sewers, etc. 1920” was directed mainly at smooth new pipes larger than 2 inches. In this original work, several items should be noted per the following quotes: The constant, 4.52, that we use in the Hazen-Williams equation today has a very interesting history. It is derived from the number .001 to the -.04 power (1.318). Hazen-Williams added this constant to their original equation to “simply equalize the value of C with the Chezy formula and other exponential formulas which may be used at a slope of .001 instead of at a slope of 1.” In the book, Hazen and Williams discuss the exponents used in their formula and the value of C. “If exponents could be selected agreeing perfectly with the facts, the value of C would depend upon the roughness only, and for any given degree of roughness, C would then be a constant. It is not possible to reach this actually because the values of the exponents vary with different surfaces and also their values may not be exactly the same for large diameters and for small ones, nor for steep slopes and for flat ones.” When speaking about deterioration of the interior of pipe when using the formula, the authors state “It is a difficult matter to handle adequately, for no two pieces of iron pipe deteriorate at the same rate, and any figures given are therefore at best only approximations to averages, which averages may be very far from individual cases. On the subject of the exponent of the slope ‘s’ (Hf / L, feet of head per foot of pipe length), The authors state the following: “This exponent shows the rate at which friction increases with velocity. Experiments with seventeen pipes have been selected as being helpful in reaching a representative value for this exponent. Each of these pipes were very smooth. The value of the coefficient actually found in the experiments is taken as the best evidence of smoothness. Many older data have been excluded, because the value of C show that the pipes that they represent were not really smooth. Data for pipes less than two inches in diameter are not included. Such data are numerous and accurate; but viscosity is a greater element in the flow of water in small pipes. Further the authors state: For rough pipes the value of the exponent s is lower, but seldom or never lower than 0.50(1/.5 = exponent of 2 versus 1.85). Perhaps 0.52 would be a representative value for old pipe. In conclusion it is worth noting that tests were made at a velocity of 5 feet per second or less; many at 3.25 feet per second. It is also important to note that the authors were considering correction of the exponents rather than changing the C value for rough pipe. Therefore, the question of what is the C value needed for rough pipe is simply a guess or assumption as the Hazen-Williams equation was predicated on smooth pipes. It is important to remember that the C value assumed for a large rough pipe is very different than the C value for a small pipe. There will be only one C value for each condition. There is no one size fitting all. The only absolute way to determine the correct C value is to accurately measure the losses with a known flow through the pipe in question. Thank You Rahe Loftin, P.E. Region 7 - GSA Office - 817-978-7299 Fax - 817-978-8644 Cell - 817-371-3102 "danarbel" <[EMAIL PROTECTED] To .com> sprinklerforum@firesprinkler.org Sent by: cc sprinklerforum-bo [EMAIL PROTECTED] Subject er.org C-Factor for old piping 02/13/2008 07:19 AM Please respond to [EMAIL PROTECTED] resprinkler.org According to 22.4.4.7 Friction Loss, The C-Factor used for black steel pipe is 120. My question is: In case of using old pipe system Mains for water supply of sprinkler system, Is there in the code any requirement to find out by actual testing that the piping determined as adequate by the hydraulic calc procedure is indeed adequate? Thanks Dan Arbel Tel: 972-4-8243337 Fax: 972-4-8243278 M: 972-52-2810593 No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.516 / Virus Database: 269.20.4/1275 - Release Date: 12/02/2008 15:20 _______________________________________________ Sprinklerforum mailing list Sprinklerforum@firesprinkler.org http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum To Unsubscribe, send an email to:[EMAIL PROTECTED] (Put the word unsubscribe in the subject field) No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.516 / Virus Database: 269.20.7/1283 - Release Date: 16/02/2008 14:16 No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.516 / Virus Database: 269.20.7/1285 - Release Date: 18/02/2008 05:50 _______________________________________________ Sprinklerforum mailing list Sprinklerforum@firesprinkler.org http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum To Unsubscribe, send an email to:[EMAIL PROTECTED] (Put the word unsubscribe in the subject field) No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.516 / Virus Database: 269.20.7/1285 - Release Date: 18/02/2008 05:50 No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.516 / Virus Database: 269.20.7/1285 - Release Date: 18/02/2008 05:50 _______________________________________________ Sprinklerforum mailing list Sprinklerforum@firesprinkler.org http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum To Unsubscribe, send an email to:[EMAIL PROTECTED] (Put the word unsubscribe in the subject field)
