Different critters all together. Soft start and stop electronically powers the pump up and down in millisecond pulses that prevent a full hit of locked rotor current on start up or the hammering effect of an instant-off stop, both electrically and hydraulically. Variable speed drives ramp the driver up or down in engine speed in response to demand, so if only a couple sprinklers or one hose valve are open, there's less pump output than if there was a huge demand downstream of the pressure sensing device. The VSD works at a "set pressure" (new definition), which is the residual that the equipment maintains as it ramps the flows up or down with demand.
One feature works at the very beginning and/or end of a run cycle, and the other one during the cycle. Steve Leyton Protection Design & Consulting San Diego, CA -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Randy Knutson Sent: Monday, February 02, 2009 4:04 PM To: [email protected] Subject: RE: - prescriptions against soft-start pumps in NFPA watersupplies.. What's the difference between a soft start and a variable Frequency drive controllers? VFD's are allowed per NFPA 20. Randy Shilo Automatic Sprinkler, Inc. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of å... .... Sent: Sunday, February 01, 2009 3:40 AM To: [email protected] Subject: - prescriptions against soft-start pumps in NFPA water supplies.. NFPA 20 & 24 water supply pumps and supply systems. We have 3 large pumps drawings from a large reservoir. water supply is devoted to a campus of buildings. these are large volume pumps, redundant. Is there an NFPA requirement that these large pumps can NOT be soft start? We have predictions of water hammer, and wish to avoid this via soft start. scot deal excelsior fire engineering _______________________________________________ Sprinklerforum mailing list http://lists.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) _______________________________________________ Sprinklerforum mailing list http://lists.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) __________ Information from ESET NOD32 Antivirus, version of virus signature database 3820 (20090203) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com __________ Information from ESET NOD32 Antivirus, version of virus signature database 3820 (20090203) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com _______________________________________________ Sprinklerforum mailing list http://lists.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)
