Spa/Pool Pipe Size Question after reading Hydraulics 101

[mas985]

Why wouldn't the valves close correctly? If the valves fail or the actuator fails, you replace it. From my experience, check valves fail more often than a 3-way valves.

I would only place 2-way valves on suction lines that are operating at the same time which would be the two skimmer lines. That way you can even up any imbalance there. Other than that, the other lines are completely isolated from one another so shouldn't require a 2-way valve.

But I just noticed in the pic above, you are showing 3 waterfall lines. Previously, you had only one line for a descent. What is the flow rate demand for those? You don't want to push too much flow rate through a filter.

 

[markmac]

I was thinking if one didn’t get completely closed, not so much fail.

there is one one 3’ descent. The other two are just water bowls with 6” descents, so 1’ total between the two.

i think the highest flow for the filter would be when running skimmers, or pushing spa overflow. But with the later, the workup you did earlier in the thread has that still pretty low And why I’m running the two 3” spa overflow return lines.

 

[mas985]

I was thinking if one didn’t get completely closed, not so much fail.

I don't see how that would happen if the valves are automated. Not a big deal if it happens anyway. Two pumps can share the same suction line if both are running. If one is not running, the flow can reverse in the off pump but that isn't a big deal either although it might drain the spa. These are failure modes that are not very likely to happen. Having a check valve fail is much more likely and more risky as it can block the entire line. But the probability of either failure mode is measured in years.

 

[markmac]

good to know and put in perspective. I'm going to update my drawing based on all this to just sanity check everything.

Based on all of this, it seems like only three check valves are really required? Two on the spa return lines and maybe the one above 3-way 'E' in my layout; to prevent backflow into the heater when running the bypass.

 

[mas985]

What is the relative height of the spa edge to the pool water? Why do you care if the spa water drops to the pool water level when the pumps are off AND the spa is in spillover mode? The spa will not drain when in spa mode. But if you really really want that for some reason, then yes you need two check valves.

You can tell I hate check valves even though I have a couple. They cause a lot of head loss, especially at lower flow rates, and when they fail, cause huge head loss. If you can avoid them, I would.

I don't think you need a check valve above valve E. Water cannot flow in the heater direction when D is shut off.

 

[markmac]

I think I follow, but believe you switched D and E. If D is set for heater bypass, water could flow back towards E. However, E would be closed, and thus still prevent water from entering the heater making the check valve redundant.

Also good to know about head loss. I assumed it was minimal to zero.

Is it worth installing an inline flow meter for any future troubleshooting? Maybe on the Spa suction side, as I could then isolate and check intake flow on either pump?

 

[mas985]

I think I follow, but believe you switched D and E. If D is set for heater bypass, water could flow back towards E. However, E would be closed, and thus still prevent water from entering the heater making the check valve redundant.

Correct. If you wanted to have E be able to switch between the pool and spa while the heater is removed, then you can add a 2-way valve on that upper heater branch. But without the heater, there is really no need to run that line to the spa other than filtering.

Is it worth installing an inline flow meter for any future troubleshooting? Maybe on the Spa suction side, as I could then isolate and check intake flow on either pump?

Each pump has a flow meter of sorts as you can set flow rate instead of RPM. Knowledge of flow rate isn't really all that useful for troubleshooting. I find pressure to be a much better indicator of problems.

 

[markmac]

What is the relative height of the spa edge to the pool water? Why do you care if the spa water drops to the pool water level when the pumps are off AND the spa is in spillover mode? The spa will not drain when in spa mode. But if you really really want that for some reason, then yes you need two check valves.

The Spa max water height will be 4"-6" above the deck. The pumps and all plumbing should be at least that or more.

You can tell I hate check valves even though I have a couple. They cause a lot of head loss, especially at lower flow rates, and when they fail, cause huge head loss. If you can avoid them, I would.

The only other check valve I was considering was on the wet side of the Air feed run from spa. The Air run from spa to backside of raised wall (opposite side of pool) would be 30', or run to the edge of the deck at 15' (more visible). Am I wrong that I can run the Air Feed 30', if I put in a check valve close to the spa, and thus no req for blower? I was thinking of adding a skimmer/autofill type cover in the deck, for any access if it fails. Then water cannot flow past the check valve, but when spa is on, it has minimal amount of water to pull before it gets air?

 

[markmac]

If I followed along correctly, I think I'm there.

 

[mas985]

The schematic looks fine.

As for the air line, 30' would probably be too long without a Hartford loop and/or check valve unless the air line is sloped upwards away from the spa. You normally you want a Hartford loop and a check valve as close to the spa as possible. Some put it in the spa wall but then access to the check valve is not possible should it fail. You could also just put a vent as close as possible to the spa but they can be a little loud.

Another option without a check valve is to put a small loop in the spa wall as high as possible and then put a second loop somewhere close by in the landscaping for easy access with a slight upward slope to the second loop. You can also avoid a check valve if the loop is high enough so water cannot travel over the loop. The objective is to only allow a small section of pipe to fill with water so the venturis can easily clear it and to keep that water as close to the spa as possible with the shallow slope. The more the air pipe fills with water, the more likely you will need a blower.

But whatever choice you make use at least 2.5" for the air line.

 

[markmac]

Hmm. I need to think how I can pull this off. With the spa being full spill over, the top of the loop if in the spa wall would never be higher than the water line. I assume that still helps as the max water that could backflow into the air line would be the max water height to loop in the wall?

My first plan was to run it straight towards the house, which would be right at 15’ from wall of spa, and then have the loop come up towards an existing hose bib so it wouldn’t look out of place. Second option was a straight shot to corner of garage (ideal as out of sight and around corner so sound not an issue), but it’s 23’. (Ignore plumbing in drawing as I’ve not updated it yet).


in both cases, I should easily create a scenario like your drawing, with one loop in wall and then slight upward slope and second loop.

once the air line comes up from the ground, does it need to stay 2.5”? That would be a fairly large, visible pipe.

 

[mas985]

For your case, the HL in the wall might not make any sense.

I would try and keep the air line at 2.5" if possible. Only the loop would be above ground.

 

[markmac]

Any harm in having the HL in the wall? Can it only benefit, by limiting how much the spa could drain down into the air line?

 

[mas985]

No harm, it just might not help much. Once water breaches the top of the loop it will create siphon so any part of the pipe that is below water level will fill.

 

[markmac]

Once water breaches the top of the loop it will create siphon so any part of the pipe that is below water level will fill.

I was afraid you might say that. I guess minimizing the distance then is key for me, and 15' seems to be as short as I can get within reason.

Curiosity question now. Could the water breach the HL full (pass the top of the loop) to create the siphon? I assume it would rise slowly with the spa off, and when it gradually started to fill the HL top curve, it would gradually start filling the dry side, not so much a siphon.

 

[mas985]

The point point of the HL is to be higher that the maximum reach of the water. Usually 6"above the water line is about as far as it will reach with momentum so having a 1 foot high, relative to the water line, should be sufficient but I might go with 2' just to be conservative.

 

[markmac]

knowing the HL is likely not of use in the Spa wall in my case, I‘m back to wondering if a check valve nearby under the Decking (accessible) is still of benefit? If the air line starts to fill, isn’t it beneficial having a check valve 5’ away from the spa to minimize how much water gets into the airline? otherwise water can run all the way to base of the Hartford loop where the pipe comes up 15’ away?

or is this where the slight uphill sloping Air Line helps instead?

 

[mas985]

My spa does not have a check valve or loop and the vent is a little over 10' away and still the venturis produce more than enough suction to clear the line. So I think you could get away without one but if you put one in, just make sure you have access to it.

The slope just helps clear more of the water to limit what is left behind.

 

[markmac]

I had one other thought come to mind, but not sure if it’s crazy or wouldn't work. Easier to describe with a visual, so attached a sketch with elevations measured starting at 0" using the bottom of the trough.

Assume I put a HL in the back wall of the Spa, where I have the spill over trough between spa and Decking. I place it as high as possible in the Gunite, and then plunge down under trough, and circle back and pop out just below coping in the Gunite. It would be out of sight with Coping overhang, open to air, and minimizes how much water could be in pipe given the extremely short run. If a siphon effect occurs, then it would just spill back into the pool. Or would the spa siphon down to pool water level? If the latter, then its not as desirable as it would drop the spa water level 9" when not in circulation.

The trough between the spa wall, and the decking is only planed to be 4"-6", so this run would be very short.

If feasible, would it still need to be 2.5"?

 

[mas985]

The spa would drain to pool level without the jet pump running unless you put in a check valve.