Calling all Fluid Dynamics Experts - Spillway Problems

[slickrock22]

We recently had our pool and spa rebuilt. During the spa rebuild we replaced a jurassic park-esque waterfall feature with a simple stone spillway. When the builder asked how wide I wanted the spillway my mind started to wonder about the pump, pump speed, gallons of water per minute on each setting and the speed needed to ensure that at the lowest speed setting, water would have enough velocity to cascade over the spillway and not roll down the front of the rocks like my neighbors (which was cover in water deposits). Since the pool was drained at the time of rebuild, and I didn't go to Yale and study mathematics and fluid dynamics, I made an estimated width with my two hands and we were off to the races.

Fast forward 12 months and now we have water deposits over the front of the rock of the spa. The spillway drips around the edge of the spillway and under and spills down the face of the rocks. My greatest fear realized. (See photos)

Now I am trying to figure out how to solve. Options from 3d printing something clear to affix to the front edge to eliminate drip and consolidate flow, replacing the stone inside to reduce the width of the opening reducing size and thus speeding up flow? (venturi effect?) - See sample photo with reduce/blocked flow - Not great either. When the pump is running at 3K+ RPM the flow is sufficient to cascade over the spillway and mostly clear the stone (but some water still drips underneath and goes down the face of the rock). I would prefer not to run the pump on full speed as it is not needed and uses electricity.

This doesn't seem like is should be so complex. Any suggestions are greatly appreciated.

Thanks!

Ryan

 

[mknauss]

An alternative idea.
As it sounds like when you run at higher rpm you do not have any issues, then set up the Spillover to run a couple times a day for 20-30 minutes to keep the spa chlorinated and run in full Pool mode the rest of the time. Then the high rpm will not be that much more cost.

 

[Jimrahbe]

Ryan,

There should be a drip slot under the bottom of the spillover.. About a 1/8th inch or so wide, and about 1/4" back from the front of the spillover.. and about 1/4" deep.

This breaks the surface tension and, in theory, keeps the water from wrapping around the lip and back against the stone.

Now all you need to do is stand in the water with an angle grinder and cut one in...

Thanks,

Jim R.

 

[slickrock22]

An alternative idea.
As it sounds like when you run at higher rpm you do not have any issues, then set up the Spillover to run a couple times a day for 20-30 minutes to keep the spa chlorinated and run in full Pool mode the rest of the time. Then the high rpm will not be that much more cost.

Thats a really interesting thought! Thanks! Now I don't think my config allows for me to isolate the pool automatically. I think I either have Spa only or Pool and Spa together. I would need to install automation valves to the spa I think. Am I think about that correctly?

 

[slickrock22]

Ryan,

There should be a drip slot under the bottom of the spillover.. About a 1/8th inch or so wide, and about 1/4" back from the front of the spillover.. and about 1/4" deep.

This breaks the surface tension and, in theory, keeps the water from wrapping around the lip and back against the stone.

Now all you need to do is stand in the water with an angle grinder and cut one in...

Thanks,

Jim R.

Thanks! Thankfully I have pool guys at the house doing some deck work and would be happy to do it. Could you send me a photo of what you are describing?

 

[slickrock22]

As an example from design perspective this manufactured spillway has an down-angled drop off vs no change in angle. I wonder if something like this is designed to get the water to leave the spillway more smoothly and further out. I might be able to mimic something like that edge in the existing stone.

 

[mknauss]

I would need to install automation valves to the spa I think.

You have an Easytouch. Do you not have actuated valves for your Spa suction and return?

 

[slickrock22]

I should have searched more. Sorry. I think this thread covers it Spa spillway advice

Options are add a metal spillway, or follow @mknauss advice and figure out hot to configure so that the spa only runs 30 min day.

Thanks all! I will let you know if I solve it any differently.

Thanks!

 

[slickrock22]

You have an Easytouch. Do you not have actuated valves for your Spa suction and return?

Yes I have actuators on both suction and return. I will need to go play with them to see if I can figure it out. I do have a Spillway mode as well.

 

[mknauss]

So you either have a spa fillup line that is used when in Pool mode or your Spa return actuated valve only partially closes. If the valve is only partially closed, then you must adjust the stops on the cam in the actuator to fully close the valve. Then set up Spillway as a Feature Circuit and schedule it. If you have the make up line, just close the valve on it.

 

[slickrock22]

So you either have a spa fillup line that is used when in Pool mode or your Spa return actuated valve only partially closes. If the valve is only partially closed, then you must adjust the stops on the cam in the actuator to fully close the valve. Then set up Spillway as a Feature Circuit and schedule it. If you have the make up line, just close the valve on it.

You were spot on. I tested spillway and figured it out. If I turn off the return to the spa that is used during the standard Pool mode the water does not overflow during normal low speed running. I have added 2 spillway schedules for 15 min each to circulate the spa water. This is also awesome because when my kids use the spa if the egg time (3 hours) ends the pump starts pumping cool water from the pool into the spa. Now with this new setting it will not. This may also keep my PH a bit more in check. Great solution. Thank you!

 

[mknauss]

Check the FC in the spa water a few times at the same time of day to be sure you are chlorinating it properly. Then adjust the spillover run times as necessary.

 

[slickrock22]

Check the FC in the spa water a few times at the same time of day to be sure you are chlorinating it properly. Then adjust the spillover run times as necessary.

Great. Will do. Thank you!