We've noticed the PLD's we've installed allow brief surge of overpressurization while the diesel starts up, builds pressure, and for the time it takes the PLD to react, there's an inrush of some of the churn pressure until the governor kicks in and backs it down. Guy at Clarke confirmed this.
We have a project with what is possibly fragile UG in many sections of the facility. We're trying to keep it, and the related interior systems, from creeping up to high pressure (isn't that why we have the PLD?). This particular site is getting twin 2,000 @ 150 diesel vertical turbines, which feed a large looped yard system, in turn feeding -oh, couple dozen risers scattered around. We're thinking a small (2.5"?) Relief valve located past the pump discharge valve, just before it drops into the yard system, PRV discharge piped back to the reservoir, set point 5 PSI above the PLD, set adjustment on reaction time to ASAP setting, so it will bleed off the excess pressure as soon as possible. We think the size of the yard loop- complete with sectionals, hydrants, etc.- will absorb the shock with only a small amount of it getting into the interior systems. If some does, 1/2" relief valves on the grid will take care of anything > 175. But we want to be able to have the UG drop back to the 155~160 range as soon as possible. Since the twin pumps go into one yard system, the small PRV only has to be installed on one of these. Since its relatively small, even if it failed OPEN the loss wouldn't de-rail the train, we have 150 @ 4,000 when combined, and demand is about 150 @3,000. Assuming the 2.5" PRV stuck open wouldn't flow more than 1,000 GPM, it could drop the water back in the hole to be re-pumped all day long. Both pumps will start remotely from elec detection systems on these large demand systems, and on pressure drop for the conventional wets. Yes, the owner has authorized high pressure testing of the UG, still doesn't mean we can slam the heck out of it or let it sit at 175+ and not see a main break in a couple yrs. Any other thoughts from those with some PLD experience? glc _______________________________________________ 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)
