I think both sides are right. and not to make up ground for too often starting the fight.
Air isn't causing over-pressure… Trevor Spain laid it out plain Air pockets are causing water-flow switch activation delays (with BFP cycling) We have two threads running in this discussion: 1. pressure relief with / without air pockets 2. corrosion with/ without freshly oxygenated water Air doesn't determine the pressure in our sprinkler system piping. The water determines the pressure in our pipes. Consider the microwave example with plastic cup of water with saran wrap; the sara expands. This in part due to heated air, but since water is opaque to microwaves due to harmonics with the covalent oxygen-water bond, the expanding saran is more due to vaporized water than any other effect. Now consider a sprinkler pipe system. Air enters the pipe at ambient pressure when we drain the water out. When we refill the pipes, some air is trapped by the filling water in high points of the sprinkler system. Liquid water fills the pipes at gauge pressure…say 60 psig, now the trapped air is at 60 psig. That is 60 psi above atmospheric. Consider a 3 story hotel in Bemidji, MN 200 ft long x 60 ft wide with a loop down the central corridor. Say we have roughly 185 gallons of volume in our pipe. It is 100% filled with liquid water (ignoring dissolved air for now), no air pockets. Assume no salts in the water either. What happens to the pressure in our Bemidji sprinkler system on a 35 F winter day, if it was filled as above on a 100F summer day? Liquid water will contract for temperatures in this range, so the volume of water decreases. How much does it decrease? … doing the math, 185 gallons of water will contract about 1.2 gallons from summer to winter. That would create a vacuum. only a vacuum would not happen. either 1.2 gallons burps through the BFP, or we will get little tiny bits of air leaking in through the fittings, only the air wont leak in. The air won't leak in because it is being pushed with only 1 atmosphere pressure while the water behind the BFP is pushing with 4 atmospheres pressure. OK, same Bemidji place, same Bemidji time, only we have a more-real system, and of the 185 gallon volume inside the pipes, there is 2 gallons of air trapped in the system with the liquid. That is 2 gallons of air at a pressure of 60 psig. If this Bemidji system we just described was filled on that same 100F summer day, what happens on a 35F winter day, assuming the static pressure is constant? Water reacts in the same way. It contracts; it has to because that is what liquid water does, at least statistically, in response to temperatures in these ranges. So the water does a group hug and gets 1.2 gallons tighter than the original 185 gallon volume. What happens to the air? It gets colder too, so its 2 gallons would shrink by 7 fluid ounces. So the BFP burps in 1.2 gallons for the hugging liquid and 0.1 gallon for the hugging gases-- as long as the static is 60 psig. What if the static pressure drops to 50 psig before winter arrives? OK, same Bemidji system, filled on same 100F day in summer with same 2 gallons of trapped air at 60 psig. The colder 35F temperature cools the gas and it shrinks by 0.1 gallon and the liquid water gets colder and shrinks by 1.2 gallons, and the BFP burps, but wait, it can't. The BFP only has 50 psig to push with and the system is pushing back with 60 psig. Or at least it had 60 psig to push with -- until the temperature dropped to winter 5F. As the liquid approaches 5F it shrinks, but so too does the gas, therefore there are competing effects of shrinking liquid and shrinking gas. From earlier examples, we saw which effect dominates: liquid contraction is bigger… So as the larger contraction of the liquid offsets the contraction of the gas, the gas expands. At the point the where the gas/air has expanded to about 2.3 gallons, the pressure in the gas has dropped to about 53 psig. The effect of the winter cold on the trapped air is enough to drop the gas pressure another 3 psig. Therefore, the trapped gas-air expands 0.3 gallons to a final volume of 2.3 gallons, and thereafter the BFP burps in water at 50 psig to make up for the remaining 0.9 gallons of shrinkage in the liquid. At least ideally. We can imagine what happens to the pressure, if the Bemidji system was filled on a cold winter day. Come that 100F burner in summer, where are we going to fit 1.2 gallons more water volume into that sprinkler system if there is a). no Pressure relief valve, or b). no trapped air of about 1.5+ gallons volume under 60 psig? the system either leaks or breaks. Gases do not start significantly deviating from ideal gas behavior until they begin approach to their critical points we are at 1/10th that value in these examples. But what about all that fresh oxygen coming into the sprinkler system via our new water pulled in from the remote ITC? How much oxygen really comes in, and does it effect MIC or is there something more to it? At equilibrium, dissolved gases in water are a function of: temperature, concentration of gases above the liquid surface and salinity of the water. The sharks and jellyfish are glad that it does, but how does the air get into the water? Around the poles, the oxygen is already in there. Phytoplankton and algae are responsible for 70% of the oxygen we breath. Fine, we don't have to worry about photosynthesizing microbes in sprinkler pipe, so how does gas get into our sprinkler water? Diffusion. Entropy. There is higher concentration of oxygen and nitrogen in the air than in the water. Colder water retains gas better than hotter water. Diffusion is improved by larger contact area. This is why winds will increase oxygen in a lake, they stir up more surface area kinda like stirring sugar into coffee. Kinda like filling a sprinkler system fast, on a cold day. In fact, if there is a long windless spell of hot weather, fish kills will occur on lakes due to oxygen depletion. Especially mountain lakes where oxygen concentration in water is lower to begin with. So back in Bemidji, in winter, and we fill that 180 gallon pipe system with cold water at 35F. How much dissolved oxygen is in that freshly introduced source of liquid water? The dissolved oxygen is at the same pressure as the water: 60 psig. But if one could get all the dissolved oxygen molecules to Cancan together, they would occupy a trapped volume of gas no more than 0.2 gallon -- or just more than what fits into one can of Ginseng Up. If we consider the nitrogen we extend that by a factor of three. Is this 12 ounce can of oxygen introduced by the remote ITC really enough to create a problem? Or could it be the mechanical action of water removes scale exposing fresh iron located deeper in the wall of the pipe -- to aerobic, albeit, non-organic oxygen corrosion? Or does the fresh water brought in by the remote ITC entrain fresh nutrients for the MIC? What about anaerobic MIC, they don't even need a can of Ginseng Up to party. they use more exotic elixirs like … chlorides, sulfides and other oxidizers. On a warm summer day in Bemidji, water holds less oxygen, about half as much as it would, if it were equilibrated with atmospheric oxygen on a winter day. The New Zealand experience and stories stateside indicate there are detrimental effects from a remote ITC. But whether the remote ITC injures by dissolved oxygen, other chemicals that abet anaerobic MIC, or simply mechanical action, the jury is still not in. And false alarms are a real problem, as anyone with the experience of interrupting their pattern for the same problem knows only all-too-well. Seems that when we do fill our systems, we want to fill them slow per Ed Vining's suggestion. Avoids turbulence that might cause removal of protective scale and it enhances dissolved oxygen. 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)
