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Thread: Correct height of surge tank water...does it matter???

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    Correct height of surge tank water...does it matter???

    Hi All

    As a newbie lookig after a large pool, I have found some excellent advice here....so here goes again!

    I have a surge tank (pool has overflow gutters to all sides) and the pump sucks straight out of the concrete surge tank (which is basically designed as per the picture attached)

    My Q is...as long as the gutters flow into the tank (by gravity) and the water level never falls below the inlet for the suction pipe......is there a "correct" water level?? ie level with pool edge etc or does it not really matter??

    many thanks again!!
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    Re: Correct height of surge tank water...does it matter???

    Is the surge tank sealed?

    Scott
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    Re: Correct height of surge tank water...does it matter???

    No, open top. Its a concerte "box"

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    Re: Correct height of surge tank water...does it matter???

    As long as it's hight exceed the pool's water level, it's fine. Water will seek it's own level and you would have a hard time keeping the pool where it should be.

    The pump needs to be able to be valved off from the tank for service purposes.

    This sounds like a commercial type setup for a large residential. You might want to get an engineering consultant that's done this to help with the planning. Most civil engineers are not qualified by virtue of the lack of experience, even if they have done dams, bridges, etc... This is not a DIY type project and given the designs you're considering, I would be surprised if a township engineer didn't ask for more engineering docs and have extra requirements for your facility that you would have difficulty providing.

    Building a gutter pool isn't cheap. If it's an indoor facility, WOW!

    Scott
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    Re: Correct height of surge tank water...does it matter???

    To back up what Scott said, you also need to make sure there is an auto-fill unit (it looks like there is one in the drawing, but I'd rather say it again than have it missed!) for the surge tank. There is also typically a static and an active elevation, with (typically) 12" of freeboard. If the pool is lower than the tank (not usually the case!) then you will need the freeboard maximum to be maintained. If the tank is below the pool (typical) then you do not want it to overflow, so you need a stop point for that elevation again. An overflow pipe higher up is also a necessity!

    Not to be redundant, but remember that you have to allow for enough tank space to handle a large surge and not overflow it also. A separate pump and filter for the surge tank is recommended.

    The plumbing diagram is not really correct. You will have your pickups for the tank in the tank, and you need your return water to go back to the pool. I'm not real sure what the main drain is supposed to be doing in this drawing. There really is no need for that if you have a gutter application (I don't honestly know when you would have a need for that application, the more I think about it!).

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    4JawChuck's Avatar
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    Re: Correct height of surge tank water...does it matter???

    Quote Originally Posted by galleymore
    Hi All

    As a newbie lookig after a large pool, I have found some excellent advice here....so here goes again!

    I have a surge tank (pool has overflow gutters to all sides) and the pump sucks straight out of the concrete surge tank (which is basically designed as per the picture attached)

    My Q is...as long as the gutters flow into the tank (by gravity) and the water level never falls below the inlet for the suction pipe......is there a "correct" water level?? ie level with pool edge etc or does it not really matter??

    many thanks again!!

    In your drawing the water level will always be the level of the pool due to the main drain connection, your drawing is a typical large commercial style pool like we have here for public pools. There will likely be a small drop in level while the pump is running due to restriction in the main drain plumbing but the water will find its own level naturally.

    In summary your surge tank water level should be at pool water level minus a small amount depending on activity in the pool and influx from the gutters etc. I doubt you will see much drop over a couple of inches unless your bottom drain is undersize or shut off, this drain is essential to the proper operation of this style system to prevent pump starvation.

    What is the problem with your setup? Is your water level the right height? Are you seeing low water in the surge tank? If you are I would check for a flow restriction in the drain plumbing or a valve throttled or shutoff, your gutters are for surge activity in the pool such as when kids are splashing around etc. Normal pool water height for this type of setup is below the gutters, you should not see water flowing over the gutters constantly when there is no activity in the pool...its there to catch the splash/surge not feed the surge tank with water constantly, thats the main drains job.
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    Re: Correct height of surge tank water...does it matter???

    Many thanks all!! some really good advice!

    This is not a new pool but existing I'm just getting involved with it, and the drawing is the closest thing to my set-up that I could find on the internet.

    I feel there maybe an issue with the main bottom drain(?) as when the pool is unused the water constantly flows over the gutters and back into the tank.
    As pointed out before, the water pumped out of the jets should increase the volume of pool water and it should find its own level with the surge tank (via the main drain)?

    How is the best way to check for a blockage in this main drain?

    Thanks again!

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    Mod Squad Bama Rambler's Avatar
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    Re: Correct height of surge tank water...does it matter???

    Here's my take on how that system should work.

    Normal operation.
    1. Pump runs and sucks water from surge tank and returns it back to pool through filter.[/*:molp93zn]
    2. Water overflows pool through gutter system back to surge tank.[/*:molp93zn]
    3. Main Drain float valve maintains a level in the surge tank to prevent the pump from running the surge tank dry.[/*:molp93zn]


    Low water level operation
    1. Pump runs and sucks water from surge tank and returns it back to pool through filter.[/*:molp93zn]
    2. Water doesn't flow through gutter system back to surge tank.[/*:molp93zn]
    3. When level gets low enough in surge tank, MD float valve opens maintaining surge tank level.[/*:molp93zn]


    If the gutter return piping was sized correctly or an orifice was installed, the water in the pool should be higher than the surge tank when the pump is running and the MD float valve should maintain a minimum level in the surge tank from the pool. When the pump is shut off the level in the surge tank will rise until the pool level is lower than the gutter system.

    Sounds like that's not happening in your system. Either the float valve is stuck open or an auto fill is stuck on, OR there's too much water in the pool/surge tank system.
    Dave J. TFP Moderator
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    Re: Correct height of surge tank water...does it matter???

    Thanks Dave

    So.....if I reduce the level in the surge tank by enough, the main drain valve should open (ball floats drop) and the pool should send water down the main drain to try to equalise? Thus telling me if its blocked or not?

    When the ball floats are fully submerged, is that valve fully closed or a little open? Just wondered if its been installed correctly???

    Thanks again!

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    Mod Squad Bama Rambler's Avatar
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    Re: Correct height of surge tank water...does it matter???

    Correct, if you lower the level in the surge tank the float valve will open allowing water to flow from the pool to the surge tank.

    When fully submerged the valve should be fully closed. They will sometimes drill a hole in the valve to allow some flow thru when the valve is fully closed. I can't see a reason for them to do that here but since I don't know how the system was designed I'm just letting you know in case.
    Dave J. TFP Moderator
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    4JawChuck's Avatar
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    Re: Correct height of surge tank water...does it matter???

    Quote Originally Posted by galleymore
    Many thanks all!! some really good advice!

    This is not a new pool but existing I'm just getting involved with it, and the drawing is the closest thing to my set-up that I could find on the internet.

    I feel there maybe an issue with the main bottom drain(?) as when the pool is unused the water constantly flows over the gutters and back into the tank.
    As pointed out before, the water pumped out of the jets should increase the volume of pool water and it should find its own level with the surge tank (via the main drain)?

    How is the best way to check for a blockage in this main drain?

    Thanks again!
    Water overflowing the gutters when there is no activity in the pool means the pool is overfilled, the gutters are for controlling wave surge or splash...they are not supposed to be the main return to the pump for circulation, thats what the main drain is for. Sounds like your floats are incorrectly adjusted and they are adding water when they aren't supposed to.

    The water level in the pool when there is no activity should be below the gutters so the main drain supplies the pump through the surge tank connection, have a look at any large public pool and you will see thats how they operate. How far below the gutters is a personal preference but typically 2" below is what I see from the two large public pools where my kids take swimming lessons. Somewhere in your system there should be an overflow to sanitary drain so if the pool level gets too high it goes out to the street, usually its just plumbed into the side of the surge tank. If you reduce the water level below the gutters does the main drain fill the sump? If it does you have flow between the reservoirs via the main drain.

    Without more details its impossible to comment on how/why your pool is operating the way it is, how about a photo?
    55 Kilolitre in-ground 18'X36' vinyl lined kidney shape, 1HP pump, Jacuzzi 250lb sand filter, RayPak Delta T 200K BTU natural gas heater. New PoolWerks "Blue Diffusion" liner on May 26th-2011
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    Re: Correct height of surge tank water...does it matter???

    With the help of the great advice above...I think its problem solved??

    I drained the surge tank, dropping the water by a good few feet. (This meant the pool was now the "head of water"?)
    The ball valves on the main drain valve were still submerged, meaning the valve was closed(?)
    I then noticed the pool lever dropping.....I then got wet in the surge tank and could feel a gentle stream of water coming out of the "closed valve" as the pool tried to equalise water levels?

    I assume that in the "closed" position, water can still gentley flow thru the valve EITHER way???
    At least the main drain is not blocked!!!

    So, to summarize....
    Do I need to set my water level (by means of automatic filler?) to be same as pool level when NOT IN USE ie just touching the gutter edge?
    How does the pump suction effect these levels??

    Thanks again! (and again!)

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    Mod Squad Bama Rambler's Avatar
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    Re: Correct height of surge tank water...does it matter???

    I think you need to valve the MD off and lower the level in the surge tank untill you can inspect the float valve to make sure it's not supposed to seal off when the float is up. I think it should seal off and not leak thru.

    The pool level should be set with the pool not running if the autofill is in the pool side. With the pool operating the level in the pool should be higher than when it's stopped.
    Dave J. TFP Moderator
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    4JawChuck's Avatar
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    Re: Correct height of surge tank water...does it matter???

    Well that explains your high water levels, your main drain is essentially closed and you are feeding fill water from potable to make up the lack of return/makeup water from the pool.

    Sounds like there is a problem or someone is trying to solve an issue with the pool water by constantly feeding fresh water into the pool, is there an overflow in the system somewhere? There must be a weir (vee shaped notch in the sump that goes to sanitary drain) in the system somewhere. There is a reason why it might be plumbed this way, the previous person who looked after the pool might have been trying to have the system constantly replenish the water in the pool to keep TDS in check. This is common in public pools where they need to meet testing requirements by changing out a portion of the pool water everyday with fresh potable water from the city water supply, its a balancing act to get the right amount into the pool while still recirculating the existing water through the filter system.

    The problem as I see it right now is you are not recirculating the water from the pool at all (return essentially closed off) and are just replenishing it from the potable supply which might cost a small fortune in water bills to keep that sump filled all the time and the overflow is going to drain. Legally your in a difficult position since changing the setup could cause a test failure by the inspector. I wouldn't do anything until you can have the system inspected by the city/county/state/provincial inspector to review what has been done and see what tests he performs and discuss the system overview setup etc.

    If this is a public pool you can be held liable for anything your doing to the pool, someone has valved the system the way it is for a reason...I would get some certified help before you open a can of worms on yourself. Public utilities are serious issues for health and safety and no one on this website (including me!) can offer advice at a distance, particularly where it involves public sanitation.

    Get an inspector in there ASAP and CYA (cover your butt!).
    55 Kilolitre in-ground 18'X36' vinyl lined kidney shape, 1HP pump, Jacuzzi 250lb sand filter, RayPak Delta T 200K BTU natural gas heater. New PoolWerks "Blue Diffusion" liner on May 26th-2011
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    Re: Correct height of surge tank water...does it matter???

    Hi Thanks!

    This is a residential pool with a manual filling outlet into the surge tank, so I know its not fresh water going in.

    Now I have both reduced the surge tank level, AND shut off the pump and all valves on separate ocasions and the pool and tank have equalised...I now know that the main drain IS connected correctly.

    However, it takes a long time to equalise (thru an 8" pipe!) so I can only assume its partially blocked??

    This means, when the pump is sucking (pool not in use) the water is sucked out faster than it can return via the main drain.
    this causes the pool level to rise and the water to overflow into the gutters.....not the worst case, but not perfect?

    Guess I'll have to live with that?

    Any sugestions on how to unblock or check for airlock in my MD appreciated!!

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    Mod Squad Bama Rambler's Avatar
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    Re: Correct height of surge tank water...does it matter???

    With it full of water and operating, there's not a lot you can do to trouble shoot that you haven't already done.

    If there's a manual block valve in the MD you could check to make sure it's completely open.
    Dave J. TFP Moderator
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    Re: Correct height of surge tank water...does it matter???

    many thanks for all the advice everyone....
    This site gives me the confidence to get more involved with my pool!

    case closed!

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    Re: Correct height of surge tank water...does it matter???

    4JawChunk says:"Main drain is essential to...prevent pump starvation"
    What if we were able to maintain water level in surge tank at a minimum?
    He also says:" You should not see water flowing over the gutters constantly when there is no activity in the pool..main drain is there to catch the splash/surge not feed the surge tank with water constantly."
    What may go wrong if we have this over flow constantly?

  19. Back To Top    #19
    4JawChuck's Avatar
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    Re: Correct height of surge tank water...does it matter???

    Quote Originally Posted by muhiratab
    4JawChunk says:"Main drain is essential to...prevent pump starvation"
    What if we were able to maintain water level in surge tank at a minimum?
    He also says:" You should not see water flowing over the gutters constantly when there is no activity in the pool..main drain is there to catch the splash/surge not feed the surge tank with water constantly."
    What may go wrong if we have this over flow constantly?

    Not exactly what I said but close enough.

    You want to extract water from the main drain to equalize temps throughout the water column, cold water falls to the bottom.

    An outdoor pool may have water overflowing the edge of the pool to act as a giant skimmer somewhat similar to a negative edge pool. Some outdoor pools I have seen have water within 1/4" of the edge so that any activity in the pool creates a skimmer effect constantly.

    What can go wrong? Not much.

    Water flowing over the sides is normal operation when there are swimmers in the pool...but its noisy, keeping the water low in the catch basin is OK too as long as the pump does not suck air. There are no absolutes just guidelines, some people keep their pool water levels right on the arrow on the skmmer face and constantly add and remove water so it stays at that mark. Myself I keep it higher than that so I always have excess to backwash with and compensate for evaporation when its hot. I've even noticed newer skimmers have a range marking instead of an arrow because really where the water level is at, is not that important as long as it doesn't cause vortexing at the pump inlet and the weir door works properly and skims as designed.

    Many of the questions you just asked are similar to what level you should keep water in your toilet tank, it will still work at virtually any level...just don't expect it to be able to flush large floating solid objects if the tank is kept low. Not quite the same thing but you get the idea.

    The beauty of these systems is they are adaptable to your local conditions and you can adjust it, in a commercial pool an overflow vee notch in the surge tank can allow you constantly replenish the pool water to control TDS or perform other related tasks like biological control. Commercial sanitation and water treatment courses teach you these things as there is no one way to accomplish goals and hundreds of different designs in the marketplace, knowing the function of the design features and how to use them to achieve your goal of sanitation is all you need to know.
    55 Kilolitre in-ground 18'X36' vinyl lined kidney shape, 1HP pump, Jacuzzi 250lb sand filter, RayPak Delta T 200K BTU natural gas heater. New PoolWerks "Blue Diffusion" liner on May 26th-2011
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    Re: Correct height of surge tank water...does it matter???

    Thank you 4JawChuck for your reply.
    I'm sure there are lots of things I must learn,that's why I asked these 2 questions and I expected you to teach me,of course in a bit more harmless manner!
    By definition a toilet tank is not working if it is not flushing those solids.But what about a swimming pool?
    Equalizing the temperature is a matter to be discussed,specially if it is explained in the terms of numbers and statistics.
    I do not really know how is that not using main drain will result in TDS control,sanitary and biological problems.

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