Hi Everyone,
I’ve hired a contractor to build an infinity pool. It is a good contractor that I’ve had experience with in the past, but our location is in South America, and this is the first infinity pool he has built. As a result, I am doing a ton of research on infinity pools to make sure none of the “rookie mistakes” are implemented by the contractor.
The main issue I’m having a problem with is the depth of the canal that receives the overflow of the infinity edges. The relatively simple calculations regarding this topic which I'm NOT having any problems with are: the overflow amount based on maximum number of swimmers, water in transit, wind “splashing” water over the edge, etc.
The estimate that IS giving me a bit of a headache is the minimum amount of water required in the canal to ensure vortexes do not form directly above the drains that lead to the pump. I’ve found many places on the internet that give me a pretty well-established equation for determining the depth required to avoid vortexes, however what I can’t find is information on what happens to that equation if you have more than one drain in your canal.
Specifics: The contractor tells me our pump pulls 105 gpm, and he is planning on using 2 inch pipes for the canal drains. The equations I’m finding on many pages online (and which are apparently based on the Hydraulic Institute ANSI/HI 9.8-1998 standard) tell me that this configuration of flow and diameter would require a minimum drain depth of 23.31 inches in order to avoid a vortex. However, that equation is only for a situation where you have one drain. The contractor is planning on installing 5 drains in the canal. My intuition tells me that the velocity at which the water will enter each drain will be evenly divided (roughly speaking – I assume some drains will work a bit better than others due to distance to the pump), so that the entry velocity at each drain will be about 1/5 of the entry velocity if there was only a single drain. As such, I suspect the minimum depth to avoid vortexes will be dramatically reduced (which would be great!), as the input velocity of each drain will be much lower – but I have not been able to confirm this intuition by my online research.
For clarity, let me ask the question another way. For example, if I were to have one drain with an entry diameter of 2.31 inches (this is obviously a theoretical value – for ease with the equations), and a flow of 105gpm, then the equations tell me that entry velocity will be 8 ft/s, and the minimum depth required to avoid a vortex will be 19.4 inches. The question is, if I add a second drain of the same diameter (connected to the same pipe/pump in serial), will the resulting velocity into each pipe be half (4 ft/s), and if so, will the minimum depth also be reduced? (I don’t think the depth will be cut in half, but I suspect the more drains, the less speed into each drain, and therefore less depth required to avoid “vortex-ing”.)
Is anyone able to confirm whether my intuition is correct (or incorrect)? And if so, will each additional drain reduce the minimum depth requirement (for vortexes specifically) in a linear manner, or will each additional drain have less and less impact to the minimum depth requirement?
(I’m deliberately not posting details of the size of my pool, because vortex creation is not related in any way to the volume of water of either the canal, nor the pool. As far as I can tell from my reading so far, the only variables related to vortex creation are depth of the canal/tank, water flow, water velocity, and diameter of the drain. Of course there are websites that get A LOT more involved, with Reynolds, Weber, etc. numbers, but I’m okay with the less complex equation that only involves the above variables; I can live with a bit of inaccuracy by erring on the conservative side of any numbers I finally arrive at.)
Thanks a ton!
I’ve hired a contractor to build an infinity pool. It is a good contractor that I’ve had experience with in the past, but our location is in South America, and this is the first infinity pool he has built. As a result, I am doing a ton of research on infinity pools to make sure none of the “rookie mistakes” are implemented by the contractor.
The main issue I’m having a problem with is the depth of the canal that receives the overflow of the infinity edges. The relatively simple calculations regarding this topic which I'm NOT having any problems with are: the overflow amount based on maximum number of swimmers, water in transit, wind “splashing” water over the edge, etc.
The estimate that IS giving me a bit of a headache is the minimum amount of water required in the canal to ensure vortexes do not form directly above the drains that lead to the pump. I’ve found many places on the internet that give me a pretty well-established equation for determining the depth required to avoid vortexes, however what I can’t find is information on what happens to that equation if you have more than one drain in your canal.
Specifics: The contractor tells me our pump pulls 105 gpm, and he is planning on using 2 inch pipes for the canal drains. The equations I’m finding on many pages online (and which are apparently based on the Hydraulic Institute ANSI/HI 9.8-1998 standard) tell me that this configuration of flow and diameter would require a minimum drain depth of 23.31 inches in order to avoid a vortex. However, that equation is only for a situation where you have one drain. The contractor is planning on installing 5 drains in the canal. My intuition tells me that the velocity at which the water will enter each drain will be evenly divided (roughly speaking – I assume some drains will work a bit better than others due to distance to the pump), so that the entry velocity at each drain will be about 1/5 of the entry velocity if there was only a single drain. As such, I suspect the minimum depth to avoid vortexes will be dramatically reduced (which would be great!), as the input velocity of each drain will be much lower – but I have not been able to confirm this intuition by my online research.
For clarity, let me ask the question another way. For example, if I were to have one drain with an entry diameter of 2.31 inches (this is obviously a theoretical value – for ease with the equations), and a flow of 105gpm, then the equations tell me that entry velocity will be 8 ft/s, and the minimum depth required to avoid a vortex will be 19.4 inches. The question is, if I add a second drain of the same diameter (connected to the same pipe/pump in serial), will the resulting velocity into each pipe be half (4 ft/s), and if so, will the minimum depth also be reduced? (I don’t think the depth will be cut in half, but I suspect the more drains, the less speed into each drain, and therefore less depth required to avoid “vortex-ing”.)
Is anyone able to confirm whether my intuition is correct (or incorrect)? And if so, will each additional drain reduce the minimum depth requirement (for vortexes specifically) in a linear manner, or will each additional drain have less and less impact to the minimum depth requirement?
(I’m deliberately not posting details of the size of my pool, because vortex creation is not related in any way to the volume of water of either the canal, nor the pool. As far as I can tell from my reading so far, the only variables related to vortex creation are depth of the canal/tank, water flow, water velocity, and diameter of the drain. Of course there are websites that get A LOT more involved, with Reynolds, Weber, etc. numbers, but I’m okay with the less complex equation that only involves the above variables; I can live with a bit of inaccuracy by erring on the conservative side of any numbers I finally arrive at.)
Thanks a ton!
