While $10,000 +/- adder on a diesel for PLD may not be offset by the savings in HP fittings, they certainly do a nice job of capping churn despite numerous other potential surprises that Murphy may have in mind for your project, such as a higher static than the flow test indicated if the tank wasn't full; future changes/improvements to the supply; ability to design in a cushion when other selections sans PLD would require HP fittings if margins were increased.
Our first PLD was used because the water purveyor was upping the pressure in the supply between 5 and 18 PSI at a 400,000 sf ESFR project, and couldn't tell us until after project completion. We now use them when we have high demand flows for storage occupancies off city supplies that have -well, even average losses between static and residual when achieving flow. Nothing like a 170 PSI hammer out to 2500 GPM to drive water down the pipe in a hurry :) and to be able to do it with churn not exceeding 170 is sweet. Finally, the "flat curve" pump underwriters always referred to is available. We also like the fact that it makes the more reliable diesel obviously cost effective vrs electric when the expensive variable frequency drive electric controls are added. Just a reminder that when determining max churn pressure, the water purveyor may have "adjusted" their flow test report to you, and that a conservative, adjusted for tank gradient water supply may be the basis of your hydraulic calculations, you must use the tank FULL static in determining max churn pressure. This need to use two different flow tests is something many designers are ignorant about, but your demand calc requires conservatism built in on the low side; the max churn determination requires conservatism on the high side. Once you think it thru, it should become obvious, but I'd venture a guess that only the nation's top 15% of designers now properly analyze this and properly adjust for tank gradient. George Church Rowe Sprinkler -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Fletcher, Ron Sent: Wednesday, February 07, 2007 9:33 AM To: [email protected] Subject: RE: pump tricks PLD (variable speed) pumps work well for limiting pressure. I think they can be pricey on an electric pump but a PLD diesel is pretty reasonable and they work. Ron Fletcher Aero Automatic Sprinkler Phoenix, AZ -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Todd Williams - work Sent: Wednesday, February 07, 2007 7:22 AM To: [email protected] Subject: pump tricks I seem to be running into several situations lately where there is a very fine balancing act between meeting the 100 psi at the top outlet of the standpipe and not exceeding 175 psi at the base of the riser. (6 story hotels are a good example) Does anybody have any good ideas they'd care to share on making these work? I'd like to limit the use of extra-heavy pipe and fitting (especially larger sizes) and PRVs. I have several tricks up my sleeve, but I'm running out of sleeves. _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum
