But if only one head activates, there is not much of an emergency, no? Brad On Jan 17, 2017 7:53 PM, "Timothy Goins" <[email protected]> wrote:
> Fine and good into you have a fire with only one had that activates. > > Therefore I say unto you, Take no thought for your life, what ye shall > eat, or what ye shall drink; nor yet for your body, what ye shall put on. > Is not the life more than meat, and the body than raiment? > MAT 6:25 > > Jesus answered, Verily, verily, I say unto thee, Except a man be born of > water and of the Spirit, he cannot enter into the kingdom of God. JHN 3:5 > > On Jan 17, 2017, at 3:16 PM, Steve Leyton <[email protected]> > wrote: > > Okay, great and wonderful but you what that does is flatten the curve and > potentially makes higher flow rate residual pressures plot HIGHER than they > would otherwise be. Soooooooo … as a designer-of-record charged with > (among myriad other things) anticipating worst case scenario, methinks it > makes sense to keep as much tilt in that flow data curve as possible. > > > > Steve L. > > (My opinion only, based on numerous cases served as an expert witness and > somebody who buys a lot of liability insurance every year.) > > > > *From:* Sprinklerforum [mailto:[email protected]. > org <[email protected]>] *On Behalf Of *Dewayne > Martinez > *Sent:* Tuesday, January 17, 2017 1:13 PM > *To:* [email protected] > *Subject:* RE: Static pressure after backflow preventer > > > > Ames got back to me and said “Yes there is a pressure loss at static > flow. It will depend on which type backflow youre looking at. A RPZ will > usually show a 10-15 PSI drop. A double check is usually 8-10.” > > > > > > *From:* Sprinklerforum [mailto:[email protected]. > org] *On Behalf Of *Brad Casterline > *Sent:* Thursday, January 12, 2017 12:51 PM > *To:* [email protected] > *Subject:* RE: Static pressure after backflow preventer > > > > Matt, > > > > I think your example of sliding friction is excellent. Pressure is force > divided by area, and force is mass times acceleration. > > With sliding friction the force required to give a mass an acceleration is > greater than the force required to keep it going a constant velocity. > > With fluid friction viscosity comes into play and is actually related to > sliding friction in that the constant force required to slide a steel plate > across the surface of a fluid, imparting a certain constant velocity to the > plate is a measure of the viscosity of the fluid. > > > > But the question is regarding friction loss when the flow is 0 GPM, and at > 0 GPM the velocity of the water = 0. > > Near the end of what I pasted you see: > > mgh=1/2mv^2. > > This is the Conservation of Energy formula for going from Potential Energy > (static), to Kinetic Energy (residual). > > In a closed system no mass is gained or lost (it is the same on both sides > so it cancels out), so, > > h=v^2/2g, and, > > v=SQRT(2gh). > > But if the velocity is 0 on both sides the only way to get a different > force measurements is with different h measurements (elevations). > > > > I know you and others know all this, so please excuse my didactic tone. > > > > Brad > > > > <image001.jpg> > > <image002.jpg> > > > ------------------------------ > > *From:* Sprinklerforum [mailto:[email protected]. > org <[email protected]>] *On Behalf Of *Matt > Grise > *Sent:* Thursday, January 12, 2017 6:33 AM > *To:* [email protected] > *Subject:* RE: Static pressure after backflow preventer > > > > Of course – if you are super close to a pressure limit – the BFP might > also lock in some unusually high pressure spike that occurs in the system. > Then the sprinkler system could sit around locked at a pressure that is > greater than even the typical measured static. > > > > Matt > > > > > > *From:* Sprinklerforum [mailto:[email protected]. > org <[email protected]>] *On Behalf Of *Matt > Grise > *Sent:* Thursday, January 12, 2017 6:30 AM > *To:* [email protected] > *Subject:* RE: Static pressure after backflow preventer > > > > Just to think out loud – I don’t have a perfect understanding of how very > low flow works through backflows… but: > > > > It seems like the system static that is locked in is usually pretty close > to the flow test static. I wonder if the noticeable pressure loss to > initially open the BFP, that goes down once flow starts, if that pressure > drop might approach zero as the flow goes from positive back to zero. > > > > That is – the pressure drop seen at a flow that is just barely over zero > depends on whether you are approaching that flow from zero, or from [more > than zero]. > > > > For example: if you slide a block across a table – the force it takes to > move the block at a very low speed will depend a lot on whether you start > from a standstill, or a faster speed. (that illustrates a different > principle, but shows how the approach could change) > > > > Thoughts? > > > > Matt > > > > *From:* Sprinklerforum [mailto:[email protected]. > org <[email protected]>] *On Behalf Of *Roland > Huggins > *Sent:* Wednesday, January 11, 2017 6:07 PM > *To:* SprinklerFORUM > *Subject:* Re: Static pressure after backflow preventer > > > > I'm flying by the seat of my pants (with no lights) but until I prove to > myself otherwise (or am beat into submission by the technical committee), I > don’t see why we should beat ourselves up and default to what ever seems to > be the most conservative. Our supply curve is a straight line relationship > from static to some lower residual pressure. We now incorporate a device > that has a crazy high initial pressure loss that then drops back into a > more normal curve. In looking at SYSTEM DEMAND are we well served by > ignoring the actual available pressure that was otherwise lost due to > accounting for a wiggle at the front end. > > > > For now, I’ll stick with my mantra: Lead the way, Mr. Custer. I’m right > behind you. > > > > > > Roland Huggins, PE - Senior VP Engineering > > American Fire Sprinkler Assn. > > Dallas, TX > > http://www.firesprinkler.org > > > > Fire Sprinklers Saves Lives > > > > > > > > > > On Jan 11, 2017, at 12:27 PM, Dewayne Martinez < > [email protected]> wrote: > > > > I have used the static without the backflow loss in the past but I noticed > with the SprinkCad software I am running it uses the mfg curves and it was > showing less static than I had figured. If I take into account the BFP > loss I can eliminate 6 pressure reducing hose valves…..Looks like I will > err on the side of caution and design them in. > > Thanks, > > Dewayne > > > > > > _______________________________________________ > Sprinklerforum mailing list > [email protected] > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler. > org > > > _______________________________________________ > Sprinklerforum mailing list > [email protected] > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler. > org > >
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