Hi Rich! Tank you for your feedback.
I think you are right on target of what I wanted and yes I live under conservative code. According to our European and Swedish rules we can not use water under the center of the pump and still call it positive head. If I understand you correctly so do you over there as well? We can still use this water, however then the pumps need different equipment to verify that the suction pipe is always filled with water (negative head arrangement). Some people over here read your NFPA rules (read NFPA 22 4.1.3) and try to interpret this to be positive head volume, just because they use a vortex plate. I agree that I have never encountered a full system fire like my calculation, but when my design is up for review that does not help. We have a few, what you might consider conservative, inspectors over here. Sometimes one can discuss with them and AHJ to find a different solution. One can argue if this is really good for our industry, if some people can get away with things not according to our code and some people can not due to personal relations with AHJ and inspectors. Best regards/ Leif Glans www.lg-sprinklerkonsulten.com LG Sprinklerkonsulten PG Vejdes vag 15 351 96 Vaxjo Sweden Phone: +46 470-74 50 25 Fax: +46 470-74 50 26 Mobil: +46 734-28 13 10 -----Ursprungligt meddelande----- Från: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] För Richard Malek Skickat: den 16 januari 2007 04:41 Till: [email protected] Ämne: RE: Positive static head for tanks Leif, Look at 5.1.2.2 in NFPA 22 specifically for welded steel suction tanks, they seem to use a different definition for net capacity. Here they define it as between the outlet opening of the discharge pipe and the inlet of the overflow. That seems as though it would be a more conservative way to define net capacity than 4.1.3. Typical centrifugal pump guidance would tell you that only water above the center line elevation of the pump would be considered positive. Personally, I don't get to hung up about it - I consider duration calculations somewhat nominal. We are not talking about a process with a real-world defined demand that will be flowing on a daily basis, etc. Do you base it on a supply calc, demand calc, where is the operating area in a real fire, how big is it, do the hose streams that get used equal a nice 100, 250, or 500 gpm. Also, I think Art was answering a slightly different question than you were asking. I think he was focusing on whether to take credit for any positive head from the tank when developing your water supply from the pump/tank arrangement. I think you were asking whether the water at the vortex plate elevation that might be below the pump center line could still be considered positive (because it is considered part of the net capacity in 22-4.1.3). This might be an area where you might not see clear guidance and alignment between 20 and 22. I'm sure you are probably aware of it, but just wanted to make one follow comment to Art's response. If you have system pressures where you are watching churn pressures, be sure to take into account the positive head from the tank in that case and watch your pump curve, particularly if it is steep and you're designing out beyond 100% rated capacity. If your real tight and using a diesel driver in particular, accounting for diesel droop will fine tune any churn calculations as well. Rich Richard Malek [EMAIL PROTECTED] -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Leif Glans Sent: Monday, January 15, 2007 3:04 PM To: [email protected] Subject: SV: Positive static head for tanks Thank you for the information Art! In Europe we say that centre of pump must be equal or lower than the lower line for calculation net capacity in tanks. Therefore, we usually end up with pump room floor lower than the bottom of the tank to minimize unusable volume or we need to have to install pumps working with negative suction head and install small tanks above the pumps to fill them with water if necessary to avoid air in the systems (Negative suction is allowed but we try to avoid it). Do NFPA have a similar rule concerning were the pump located and positive head? (I could not find when I did a search in my PDF version) Some people over here argue that if one uses a vortex plate one can still use this volume even if one have a pump room floor levelled with bottom of the tank and as well be on the positive head. If I understand you correctly, they are wrong? Why am I telling you this, well now we (in Sweden) need to use NFPA rules for EC sprinkler, ESFR, etcetera as well as our own standard (Swedish) which are on top of European standard. It starts to be vary confusing with all this rules and I just try to find some common ground. I'm sorry for my bad English. I hope that you understand me. Best regards/ Leif Glans www.lg-sprinklerkonsulten.com LG Sprinklerkonsulten PG Vejdes vag 15 351 96 Vaxjo Phone: +46 470-74 50 25 Fax: +46 470-74 50 26 Cell: +46 734-28 13 10 -----Ursprungligt meddelande----- Från: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] För art Skickat: den 15 januari 2007 20:23 Till: [email protected] Ämne: RE: Positive static head for tanks NO. As the tank empties or reduces to zero this head disappears. Assume the tank is nearly empty. That is the static head. If the tank is on a hill the elevation from base of the tank will provide you some static head. Art ATCO FIRE/Tiroly & Associates -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Leif Glans Sent: Monday, January 15, 2007 12:26 PM To: [email protected] Subject: Positive static head for tanks Hi! If one uses Centrifugal Pump according to NFPA 20, one should not use it if static suction lift is required (6.1.2, A 6.1.2) According to NFPA 22 4.1.3 for suctions tanks, the net capacity shall be the number of cubic meters (U.S. gallons) between the inlet of the overflow and the inlet of the vortex plate Is all of this volume considered positive head according to NFPA? Best regards/ Leif Glans www.lg-sprinklerkonsulten.com LG Sprinklerkonsulten PG Vejdes vag 15 351 96 Vaxjo Sweden Phone: +46 470-74 50 25 Fax: +46 470-74 50 26 Cell: +46 734-28 13 10 _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum
