Hey Tom, Without explaining all of the math, if your system is 10,000 gallons and you already had it full of water (I think you said you could fill to 70 PSI from the city supply), with no air in the system, you would have it pumped up to 200 psi with your little 4 GPM pump in less than 12 minutes. If there is 1,000 gallons of trapped air in there, that would add about 4 hours. The real world will change these numbers, but I think this illustrates my point of how important it is for your timing to get as much air out as possible, and also that it is still very possible to do it with your little pump. If you are trying to do an initial fill of the whole system with a little pump/hose, that is a different story.
-Skyler On Sat, Apr 17, 2021, 6:19 PM Tom Duross via Sprinklerforum < [email protected]> wrote: > Thanks Skylar, all too experienced in venting from previous bad > experiences back in the day. > The underground we did yesterday we fortunately had 2 hydrants and the 8" > flanged stub in the pump room to vent. The stub was where we flushed from > (to get the entire main) and also pressure tested/forward flow tested > from. I welded up a set of manifolds years ago with 2.5" grooved weldolets > that take grooved hose valves. We vented the hydrants and also through the > manifold and even with a slight dip in elevation between hyd. 1 and 2 > before entering the building I think we got 'most' of the air. I can > usually tell in the first 10 minutes, depending on volume, if we got > trapped air. I use a good calibrated gauge (pump gauge) and saw an initial > drop from 210 to 207 in the first 10 minutes but rock solid after to 2 > hours. > > These roadway babies are all over the place but, we have AAV's at every > elevated station. 6 coupling expansion joints. The AAV's have ball > valves on them so I figure 2 passes end to end should vent, check the hose > valves for tight an caps tight, close the ball valves on the AAV's; all > under street pressure. The trick, well one of them, is going to be > checking for leaks, like I’m going to hang my fat head over the side 75' in > the air, and then find a pump suitable for the initial charge, and maybe > recharge. Looking. > > I also have a clause in discharging dirty water that I didn't before, plus > one for noise. We are close to the harbor and old Ironsides so we may have > to run hoses to a sanitary manhole, we still have catch basins that drain > to the ocean. I'm excited to do this, despite the conditions, I'll be > taking pictures and video unless the Commonwealth says no. They did during > the big dig. > Any advice or help is appreciated guys. > > > Scot - I don't think your base equation is quite right. You may be trying > to use the ideal gas law here, on a liquid, which doesn't work. Also, I > think technically you would be changing "n" in the equation, not V (the > volume of the system is constant at P1 and P2), but I don't think this > really matters. I think your equation is essentially correct, but only if > we were talking about a system being filled and tested with a gas, not > water. > > Tom - I have considered this problem in the past, when I had to test a run > of underground piping in the middle of nowhere, and I wanted to know how > big of a tank I would need to bring to get to 200 psi after the piping was > full of water. Because water does not compress very much (see link below > for a graph; less than .5% at 1000 PSI), the answer was extremely small > (less than 10 gallons). I don't want to run through the math again (it > doesn't really matter because we are talking about only needing to add a > very small volume of water to increase the pressure substantially). The > huge key is having no air in the system. Air is very much compressible, as > shown in Scot's equation. I say all of this because my advice is that you > should vent out as much air as possible. If you can do this, it shouldn't > take much time to pressure up the system up to 200 psi, even with a small > pump. Getting all the air out is usually easier said than done (theory can > be much different than real life), but with what I just told you, it is > worth making an attempt. > > > https://www.quora.com/How-much-force-would-be-needed-to-compress-water-within-an-indestructible-vessel-And-what-would-happen > > > Thanks, > Skyler Bilbo > > 1700 S. Raney Street > Effingham, IL 62401 > 217-819-6404 Cell > > [email protected] > www.wenteplumbing.com > > > On Fri, Apr 16, 2021 at 3:27 AM å... .... via Sprinklerforum < > [email protected]> wrote: > > > To answer your question: > > > > *P1 *V1* = P2 * V2 when tested at close to the same temperature. > > V2 = (P1*V1)/P2 where P1 = 200 psi/14.7 psi = 13.6 atm, V1 = > > volumen of your pipe system, P2 is 1 atm. > > V2 = 13.6 * V1 > > If we have a 4 gpm pump, replace V2 with (4 gpm * x min), rearrange > > to solve for minutes. If we have 2 pumps operating in parallel, we > > use the flow rate of the pump with the lower developed-pressure. V1 is > in gallons. > > > > X minutes to fill = (13.6 * V1 ) / 4 gpm * FF > > > > FF is a fudge factor. It accounts for leaks, the fact that your pump > > may not be exactly 4 gpm, the fact your pump flow rate will decrease > > as the pressure it pushes against increases, and FF accounts for plain > and simple > > entropy. My hunch is FF is about 1.3. But don't take my word for it, > > record the results yourself and show how bad this hunch is. > > > > "The inspector came back after the requisite 2 hours and signed it off. > > It's > > all about relationships." > > > > _______________________________________________ > 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
