What if drains are NOT contributing to circulation? How might that change your world?Most of the content of this blog was supposed to appear next week, but I received a tragic email this morning and it's been troubling me...A man (husband) was killed on the drain of a pool on April 11th in Pittsburgh. We don't have many details yet, but this appeared today on the newsfeed:Wife of man who drown at athletic club files wrongful death suitIt will be interesting to see if this pool actually NEEDED a drain other than the great state of PA mandating one. Time will tell, but history records and sometimes it is history that teaches us the best lessons.So let's take a look at language on circulation for all, but about 9 states in 1928:VII. Inlets and OutletsA. All pools should be provided with an outlet at the deepest point of sufficient size to permit the pool to be completely drained in four hours or less. Outlet opening in the floor of the pool should be at least four times the area of the discharge pipe ,to reduce suction currents. This opening must be covered with a proper grating.B. In rectangular pools with deep water at or near one end, multiple outlets should be provided where the width of the pool is more than 20 feet. In such cases outlets should be spaced not more than 20 feet apart, nor more than 10 feet from side walls.C. Proper pipe connections must be provided in recirculation pools to permit water being drained directly to the sewer, as well as to recirculation pumps. In making connections of pool outlets with sewers proper care must be taken to prevent any possibility of sewage from the building or from outside backing up into the pool.D. Inlets for fresh or re-purified water should be located to produce as far as possible a uniform circulation of water throughout the entire pool. In semi-artificial pools of irregular shape a careful study should be made of probable circulation currents and inlets located and spaced to provide as complete circulation as possible. All inlets should be located at the shallow water portion of the pool and not more than 1 foot below water line, except in case where reverse circulation is used as discussed in paragraph H.E. Where the distance across the shallow portion of the pool is more than 20 feet, multiple inlets must be provided, so spaced that each inlet will serve a linear distance of not more than 20 feet. At spoon shaped rectangular pools where the outlets are located more than 5 feet from the end wall, inlets should be placed at both ends of the pool. At large pools with outlets near the center, inlets should be placed at the specified intervals entirely around the perimeter of the pool.F. In small rectangular pools with only a single inlet and a single outlet, inlet and outlet should be located on a line drawn lengthwise through the center of the pool. Inlet orifices located at or below normal water level should be covered with a grating having openings of at least twice the orifice area.G. Each inlet should be designed as an orifice and proportioned to supply the volume of water required at that particular point to obtain the best circulation. Inlet piping should be designed to provide at least, twice the area of the inlet orifice. In large pools the inlet pipe system should be designed in sections with gates to permit regulation of the flow to different inlet orifices.H. In a few cases pools have been designed for fresh water or re-purified water to enter at the deep point and overflow through outlets or skim gutters in the shallow portion. It is believed there may be some advantage in having flow through the pool in this direction, thus permitting floating matters and dirtier waters from the more crowded shallow area to be carried off more rapidly. The committee suggests that in designing piping systems for recirculation or flowing through pools, cross-connections be provided so that flow through the pool may be in the direction which experiments may prove most desirable. It is also suggested that the question of having skim qutters serve as overflows and outlets in recirculation or flowing through systems be studied more carefully, as it appears that such design may have certain material advantages.Can you imagine that? it's concise, it's accurate, and best - it does not conflict with the know physical laws of fluids. Oh yeah, this was a day when circulation systems were circulation systems and a drain....was a drain.Just imagine if we built pools like this today? How did we get the 80/20, 60/40, 50/50 nonsense mandates? Where did we forget what was happening and why? These are all the questions I have and I am spending some time digging in to find out. Pools were SAFER by these design standards than they are today. When you think of something new, like ANSI/APSP-7 and know how many PAGES are included to deal with drains only to find out that we could eliminate ALL submerged suction like they did at the turn of last century.As you may have seen in Solutions for Suction Entrapment forum on PGN, we recently had a debate and I offered what I believed to be a simple thought experiment. Take a 100 ft x 85 ft x 4.5 ft (ave depth) public pool. Its 286,130 gallons. A 6 hour turn would yield 795 GPM, which can be handled (volume) by a single 18 x 18 drain cover that has been tested to ASME A112 19.8 (2007) as SAFE as a single suction. The drain is less than .026% of the floorSo let's propose the following question:Assuming ALL flow is going to the drain for this particular pool, what are the chances that debris on the floor will find such a small spot?Before you answer, consider that the drain has an area on the floor of 2.5 sqft and the pool is more than 8500 sqft (did not include the slope).We all know that a drain is going to have little influence on dead spots some 100 or more feet away, it doesn't have significant effect at ELEVEN INCHES. What is also suspiciously missing is any nonsense about "circular motion of the water." In fact, the writers went to great lengths to attempt to create "plug flow" where drains WERE used. They put LIMITS on where the returns would be to encourage the water to flow towards the pool - entraining dirty water on the way to the drain. It was a North American standard so they did not consider coriolis effect and toilets flushing in Australia either. [Side note: if you think the rotation of the earth has an effect - read this]. We know that the number of inlets scale with a pool as does the turnover in GPM, but we need only one drain at the "deepest point" for proper circulation? No, we don't and now we know why it ended up there. We need not go past its legacy name, DRAIN, for the answer. It was to drain the pool. Today, we don't use drains to drain pools, we you submersible or deck mounted pumps. They are faster and save the pool equipment from needless wear and tear associated with draining a trash-ladened pool on season startup.I find it amazing that not only is this language COMPLETELY accurate AND concise, it counters MOST if not all of the folklore that plagues our industry today. Antidotal evidence of cloudy pools associated with no drains, etc...don't really stand up when one actually goes out and measures what is going on - there are always other explanations. I don't want anyone to feel embarrassed by the blatant statements that go counter to what you are taught. While this is important, in the grand scheme of construction schedules, plaster, steel, gravel, tile, piping, can you save my sod...and the prized butterfly bush you just demolished, knowing the details and physics behind circulation is really a LOW priority. One can't really do much with it in the field and we are working now to include some of the basic guidelines in our next generation standards.What I do have a problem with, especially in light of someone's husband, daughter, son, grand daughter, etc...dying, is the complete unwillingness to LEARN. Folks, this is not debatable with any merit. There is not one person that is actually competent in fluid flow that would argue this point.Drains don't move water, inlets do. It's really that simple. Drains can be used to RECEIVE water, but as we can see from our well thought out standards of yesterday, it's going to be difficult with the type of pools we build today and most of our standards would not let us BUILD the pools above - they were right then, we are wrong now.Benjamin Franklin's first TWO patents were swimming devices and he also wrote a book on swimming. He once said,"Being ignorant is not so much a shame, as being unwilling to learn."Nothing could be further than the truth.
In Ohio, the Ohio Dept. of Health is currently reviewing, changing and amending the Public Swiming Pool, Spa and Special Use Pool Rules. We recommended to the rules committee that main drains no longer be required on all new builds and that existing drains be changed to returns and equipped with VGB approved grates. Our suggestion did not go over very well.
Anyway, I used the example of a match. Strike a match then blow it out....then strike a match then try to suck it out. Obviously, it is much easier to blow out a match. We thought this was a very simple example, but was told that drains are and will remain a requirement on all pools.
The bureaucracy needed to make a change is ridiculous even if in the best interest of "public health".
I agree totally with what you talk about not needing main drains. We changed drain covers on over 300 pools to be VGB and noticed how much dirt was on the bottom of the sumps. If the drains were suppost to be cleanng the pool from he bottom, there should not have been dirt in the drain sumps. I would also be interested if the covers on the pool in PA. were VGB approved.
"H. In a few cases pools have been designed for fresh water or re-purified water to enter at the deep point and overflow through outlets or skim gutters in the shallow portion. It is believed there may be some advantage in having flow through the pool in this direction, thus permitting floating matters and dirtier waters from the more crowded shallow area to be carried off more rapidly. The committee suggests that in designing piping systems for recirculation or flowing through pools, cross-connections be provided so that flow through the pool may be in the direction which experiments may prove most desirable. It is also suggested that the question of having skim qutters serve as overflows and outlets in recirculation or flowing through systems be studied more carefully, as it appears that such design may have certain material advantages."
Ray,
I too am curious what turned us away from this logic. I can see no reason why the existing drains cannot and should not be reversed. Alterations can be made to adjust flow rate, and we completely eliminate the entrapment issue. Making the "drain" a return just seems to solve the whole issue.
Of course, any change to a piece of the system changes the whole system, so what effect might I be missing by reversing the flow?
Comments
In Ohio, the Ohio Dept. of Health is currently reviewing, changing and amending the Public Swiming Pool, Spa and Special Use Pool Rules. We recommended to the rules committee that main drains no longer be required on all new builds and that existing drains be changed to returns and equipped with VGB approved grates. Our suggestion did not go over very well.
Anyway, I used the example of a match. Strike a match then blow it out....then strike a match then try to suck it out. Obviously, it is much easier to blow out a match. We thought this was a very simple example, but was told that drains are and will remain a requirement on all pools.
The bureaucracy needed to make a change is ridiculous even if in the best interest of "public health".
Ray,
I too am curious what turned us away from this logic. I can see no reason why the existing drains cannot and should not be reversed. Alterations can be made to adjust flow rate, and we completely eliminate the entrapment issue. Making the "drain" a return just seems to solve the whole issue.
Of course, any change to a piece of the system changes the whole system, so what effect might I be missing by reversing the flow?