Thank you Chris, it is good to hear from the voice of experience. Ron Fletcher
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Chris Cahill Sent: Wednesday, July 09, 2008 9:05 AM 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) _______________________________________________ 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)
