Frans, I think you just described the main difference between the European and American approach to fire protection. If you want to find out why 20 changed you can go back to the ROP/ROCs and see the proposal, who submitted it, the rationale behind it, and committee commentary. This, I know is easier said than done, but it is available and for issues that occurred in the nineties forward easier than the whys changes from many decades ago.
On Mon, Apr 5, 2010 at 12:36 PM, Frans Stoop <[email protected]> wrote: > Roland, > > The technicians that I have to communicate with don't take "it's a > very bad thing" for an answer. > They like to know why it is so bad. They even don't take the wording > "shall not be used" as it is in the current NFPA 20 edition as a > sufficient reason not to do it. > > Regarding the past: there was no reference in the 1996 edition of > NFPA 20 about not using the pressure relief valve to limit the > maximum pressure. > Even the Fire Pump Handbook (1998) makes no reference to this issue > in its commentary text. > > The first appearance that I found is in the Appendix of the 1999 > edition where it is called "poor design practice". > > In today's edition the wording "shall not be used" is in the main text. > My reasoning is that somewhere between 1999 and today the committee > must have had good reasons to decide to change the wording and forbid > the use of the pressure relief valve to limit the pressure. I'm > curious what that reasons could be. > > Regarding dumping the water in the parking lot: The cases I refer to > are mainly industrial plants. The fire water is usually taken from a > large suction tank. The discharge of the pressure relief valve is > piped back to the top of that tank. So nobody is troubled by the > discharge and the water is not wasted. > > The high pressure in the point of operation happens when there are > one or more design areas on a high elevated places (like happens e.g. > in power plants). At the same time there are components on ground > level that are only available in 175 psi design (like dry pendents > and ESFR sprinklers). > There are quite a lot of watersupplies overhere that use the pressure > relief valve for this purpose if a high operating pressure is > required. And what worries me more: even in new installations it > seems still a popular way to limit the pressure. > > However, thank you for sharing your point of view. > > Frans Stoop > TOS architecture & fire protection > Netherlands <[email protected]> > Tel. +31-24-324 0112 > > At 09:42 2-4-2010 -0700, you wrote: >>doing a very bad thing all the time is not grounds for continuing to >>do it. NFPA 20 did not allow it in the past although the sloppy >>wording lead many to jump to that conclusion. The problem is during >>the weekly churn test, you are dumping a boat load of water in the >>parking lot etc. It now emphasizes that one is to design the system >>appropriately and account for higher pressures by selection of >>components (including not casually going to a bigger pump just to get >>a little more pressure and down size the pipes just a touch more). >>That's about as bright a light as I can shine. >> >>Roland >> >>On Apr 2, 2010, at 8:54 AM, Frans Stoop wrote: >> >> > Forumites, >> > >> > NFPA 20 - 2007 par. 5.7.6.2 ( = 2010 par. 4.7.7.2) says: >> > "Pressure relief valves and pressure regulating devices in the fire >> > pump installation shall not be used as a means to meet the >> > requirements of 5.7.6.1." (= 2010 par. 4.7.7.1) >> > >> > I ask this question because it seems to be not unusual in my country >> > to fit fire pumps with a pressure relief valve to limit the churn >> > pressure below 175 psi in systems that need a high pressure (e.g. 165 >> > psi) in the point of operation. Thus flattening the first part of the >> > curve up to the point of operation. >> > This happens to both, engine driven as well as electric driven fire >> > pumps. >> > In engine driven pumps they use for this purpose the same relief >> > valve as mentioned in section 5.18 "Relief Valves for Centrifugal >> > Pumps" (= 2010 section 4.18). >> > >> > Can anyone tell me why this par. 5.7.6.2 says: "shall not be used" ? >> > Why did the committee put this in the code ? >> > I remember times when it was not in there. >> > Is this based on bad experiences? >> > >> > When I point other technicians to this rule a common response is "Why >> > ? We do it all the time! " >> > >> > Can anyone of you shed some light on this issue? >> > >> > Frans Stoop >> > TOS architecture & fire protection >> > Netherlands <[email protected]> >> > Tel. +31-24-324 0112 > > _______________________________________________ > Sprinklerforum mailing list > [email protected] > http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum > > For Technical Assistance, send an email to: [email protected] > > To Unsubscribe, send an email to:[email protected] > (Put the word unsubscribe in the subject field) > -- Ron Greenman Instructor Fire Protection Engineering Bates Technical College Tacoma, WA Member: SFPE, ASCET, NFPA, AFSA, NFSA AFAA, NIBS, WSAFM, WFC _______________________________________________ Sprinklerforum mailing list [email protected] http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [email protected] To Unsubscribe, send an email to:[email protected] (Put the word unsubscribe in the subject field)
