Chris, I respectfully disagree having had synthetic TPX do just that at negative pressure, its simply not designed for suction use. Its even more likely to occur where the supply line has been kinked or angled such as at the point of connection. The negetive pressure reading in of itself is indicative of water pressures below atmosphere. At some point atmospheric pressure will excert force on the non rigid hose jacket no different then when the source of pressure is removed from the hose line and it deflates.
I agree however that transient digressions below zero arent going to result in total collapse of the fire departments water supply. However there are situations, such as the opening of another hydrant upstream that could result in loss of water pressure to engines downstream. My experience with TPX is that it will not remain rigid and will not support water be drawn at vacumn from the source. Its really a moot point however, at least in New Jersey, and I'm sure theres other jurisdictions that have adopted the IFC or AWWA to establish fire flows. Fire flow requirements whether they be privately supplied or publically supplied are a function of the local jurisdictions fire protection requirements. If a jurisdiction adopts IFC Appendix B, or for that matter AWWA M31 as its fire flow criteria then its immaterial as to the ownership and/or provider of the water supply, the water must be provided accordingly. We can go round and round on this one, if the design's at 10psi and the fire departments operating at 20psi the fire flows simply not going to be achieved. But not to worry heres the code references that require the design at 20 psi residual; For example New Jerseys Residential Site Improvement Standard (RSIS) states; 5:21-5.2 Capacity (e) The design of the on-site water distribution system shall be adequate to provide fire protection as per ISO standard, Fire Suppression Rating Schedule, or per AWWA M31, Manual of Water Supply Practices -- Distribution System Requirements for Fire Protection, ISO method on pages 3-9, incorporated herein by reference. AWWA M31 Chapter 1 - Fire Flow Requirements "The following definition of required fire flow will be used in this manual; the rate of water flow, at a residual pressure of 20 psi (138kPa) and for a specified duration, that is neccesary to control a major fire in a specified structure." 5:21-5.4 Fire Hydrants (a) Hydrants shall be spaced to provide necessary fire flow. The average building area served per hydrant shall not exceed 120,000 square feet. In addition, the distance between any dwelling and a hydrant shall not exceed 400 feet when measured along the street right-of-way. John Drucker Fire Protection Subcode Official (AHJ) Firefighter New Jersey -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Chris Cahill Sent: Wednesday, July 09, 2008 12:05 PM To: [email protected] Subject: RE: FD Pumper Suction Hose Soft suction doesn't collapse even at negative gauge pressure at the truck. I've done it many times teaching new drivers as an exercise teaching them 20 suction is a good guide but if I'm in the building they better be able to take it down past zero if necessary or eat my haligan if I run out of water. Don't forget the velocity of the water having the effect of keeping it open. We're talking large diameters here. To get negatives in the hose you have to flowing a bunch of water (technical term). Takes more than a few negative psi normal pressure to stop the water. At 1000 gpm that's 140 lbs of water a second moving forward. I'm sure there is a limit and it probably has more to do with cavitation in the pump by starting to boil the water due to low pressures. If the water boils the pump no longer is flowing the same volume and with decreased volume the pressures come back up. Could be a self correcting problem but I wasn't willing to risk damaging a pump. As others said though 20 is the right number at the hydrant for the code compliance in IFC and contamination in AWWA, has nothing to do with suction hose IMHO. Here's an interesting twist to consider. The IFC typically wouldn't apply to public utility design, just like NFPA standards don't. So with that theory the 20 actually only applies to private hydrants not public hydrants, which is the original question. At least in these parts the water utilities are independent gov't agencies and the state has no law governing the design of public utilities ability to provide fire water at any volume or pressure. Certainly could be a mess if an AHJ tried to apply IFC 508.2 to a rural area and even some parts of some very large cities. Chris Cahill, P.E. Fire Protection Engineer Sentry Fire Protection, Inc. 763-658-4483 763-658-4921 fax Email: [EMAIL PROTECTED] Mail: P.O. Box 69 Waverly, MN 55390 Location: 4439 Hwy 12 SW Waverly, MN 55390 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Ed Kramer Sent: Wednesday, July 09, 2008 9:42 AM To: [email protected] Subject: RE: FD Pumper Suction Hose Ron, I'm not familiar with fire dept operating procedures (you've gotten pretty good input from that perspective from others). Just a couple comments that have to do with simple hydraulics: Due to friction loss, 20 psi at the supply hydrant will equate to something less than 20 psi at the pumper truck. If the pumper truck happens to be located higher than the supply hydrant, the elevation difference will decrease the 20 psi also. The 20 psi seems like a reasonable (though somewhat arbitrary) safety margin to prevent soft suction hose from collapsing. Ed Kramer Littleton, CO > Does anyone have experience with 4" pumper truck suction hose of the > soft variety? According to a City FPE Phoenix FD requires 20 psi > (flowing) at private hydrants to avoid collapsing the soft suction hose. > Sounds fishy to me but I have no way of knowing. > > I can understand not taking the city main below 20 psi but I don't see > why a private fire main can't go below 20. > > Ron Fletcher > Aero Automatic > Phoenix, AZ _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum To Unsubscribe, send an email to:[EMAIL PROTECTED] (Put the word unsubscribe in the subject field) _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum To Unsubscribe, send an email to:[EMAIL PROTECTED] (Put the word unsubscribe in the subject field) CONFIDENTIAL AND PROPRIETARY: This email message is intended only for the use of the individual or entity to which it is addressed and may contain information that is privileged and confidential, nor is it, unless specifically stated, intended to be relied upon by any person or persons other than the individual or entity named above and no warranties or representations are made or intended to persons or entities not named above. If the reader is not the intended recipient, you are hereby notified that any dissemination, distribution or copying of this communication is strictly prohibited. If you have received this communication in error, please notify us immediately by telephone, return this message to the address above and delete all copies. Thank you. _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum To Unsubscribe, send an email to:[EMAIL PROTECTED] (Put the word unsubscribe in the subject field)
