Solar pump runs dry ~45seconds each time - Check valve required?

[paulr33]

Hi All,

I have a fibreglass salt water pool (45k litres) and the pumps are about half a meter above the pool level based on the backyard landscaping. The solar pump is a Viron E140 and it works well and is able to maintain the system etc all works well, but when starting each time, it runs dry for at least 45 seconds if not more (could be over a minute).

I believe the pool installer put a check vavle after the pump to stop water flowing back off the roof and back to the pool, but my question is, should there be a check valve in front of the pump so that built up (prime/vacuum) pressure doesnt flow back to the pool at pump shut off?

The main pool pump doesnt have this issue (dry running) and doesnt use check values that I can see of.

Here is the solar install;


I am working on a Pool adruino controller to monitor pH, ORP and temperature so I am keen to share this with the community when I have it working. I've documented it briefly on paulr33.com if you are curious.

Thanks for your help

[Denniswiseman]

That original lay out should work, I suspect that you have an air leakage between the NR check valve and the pump / pool, does the pump basket drain out when the pump is off
The problem with solar is it should drain out each time to prevent freeze damage or excessive overheating when the pump isn't running
If you can't find the suction side air leak I would be inclined to remove the NR check valve that is keeping the solar panels primed and place it on the pump inlet as shown in your image, this would keep your pump and suction side primed

BTW
paulr33.com doesn't show anything yet

[Teapot]

All I want to add is, Is this a recent issue or has it always done it?

[paulr33]

it has always done it, no chance since install, approx 1 year old setup
runs dry for over a minute each time, only a tiny bit of water remains in the pump swirl pot when powered off

[Teapot]

Dennis was correct to reckon on an air leak but if it has always done it can you get the installer back to put it right? (This makes a big assumption they are capable of doing so)
Personally where I have go out to pumps mounted above the waterline I fit a non return valve as close to the pool as possible (but still accessible) to maintain a primed supply. I much prefer re engineering to do away with the bad practices of last century.
Why was mounted so high? Doing that just makes hard work and more wasted energy.

I have met loads of pool installers and I am not impressed with their overall lack of knowledge, just last month I was sat in a room full and only one guy knew anything and two were so stupid that they stopped talking as every time they opened their mouths they just confirmed they hadn't a clue, wonder if their customer knew?

What is your main pump? A little surprised you need two, how high up is your solar?
On another forum a guy with a similar setup and we calculated how much extra electricity the pumps need to run his solar. If he converted that to a heat pump he actually used less and didn't have to wait for the sun so he could use cheap rate night electricity.

[Denniswiseman]

When the pump is primed and running correct do you notice any water leak around the pump?
If water comes out air can get in especially around the pump basket lid. You could try spraying some shaving foam over your NRV and pump to see if any gets sucked in when you stop the pump

[Teapot]

How quickly does it loose prime 10mins, 1 hour, overnight? Can you un-couple to see if the non return is letting by. So many questions when not actually there to see it.
That little temperature probe looks a bit suspect to.

[paulr33]

thanks for the info, i will try the shaving cream trick to see if i can locate any air leaks
i do not get any water leaks on or around the pump etc. the prime is lost each time as soon as the pump is turned off. so if its running right now and i turn it off, then back on, it will take another minute at least before it starts flowing again.

the solar system is installed on our roof and the solar pump and main pump are above the pool level about half a meter higher based on the landscape and land heights and where the pumps are located. this was our preference based on pump install location.

[Denniswiseman]

thanks for the info, i will try the shaving cream trick to see if i can locate any air leaks
i do not get any water leaks on or around the pump etc. the prime is lost each time as soon as the pump is turned off. so if its running right now and i turn it off, then back on, it will take another minute at least before it starts flowing again.

If it is instant as you say, It could be the NRV on the pump outlet not working correctly and allowing all the water to drain down to the pool via the pump
Is it easy to disconnect the pipe above the NRV to see if there is any water left in the pipe to the solar panels

[Teapot]

Seconded!

solar pump and main pump are above the pool level about half a meter higher based on the landscape and land heights and where the pumps are located. this was our preference based on pump install location.

That's why I never give that option to customers, they don't know enough about the hydraulic circuit.

[paulr33]

did some checking today. at power on, water starts flowing slowly into the swirl pot at 45 seconds. at 2 minutes the pump has enough prime for full flow and works normally from here on wards. when i turn the pump off instantly i can see some water flow back over the swirl pot but its only a couple of seconds, i wouldnt say its a full roof of water if that makes sense? its only a small flowback amount. but there shouldnt be any if the check valve is working? maybe he didnt install one?

here is the pipework;

at pump off, from doing a tapping test, i can tell there is water in the sections marked as green pipework. the sections marked yellow do not have any water in them at pump off. so it looks like the water pools only in the lowest gravity fed sections of the pipework and not the entire pipework.

there is also a joiner rubber tube as shown that joins both pipes, is this a breather tube?

[Denniswiseman]

It doesn't look like there is a NRV installed
The reason why the green section has water in it is because there is a loop and it will always have water in it
I suspect that the problem is that the pump has to try and push that water while there is air in the pump
Do you know why that pipework is looped down? If you repipe it so it doesn't loop it may work better

[Teapot]

Looks like a knuckle bend party!
If there has ever been a case for a NRV in front of the pump that's it.

It depends how much work you want to do obviously but removing some of the knuckle bends would allow you to wind down the pump a bit and save some bucks. I wonder what your main pump is and if it has enough grunt to lift the water around the heating?

[paulr33]

the big U shape bend is probably there because the solar pipework is installed by one company, then the pool installer installs the pumps and other stuff and the pipework is at different heights so he probably made it a big u shape to connect it all instead of redoing it properly. he did say a check valve was installed but maybe he never did it (wouldnt surprise me).

i can get my local plumber to fit one, no problems, should it go somewhere specific? as close to the pump outlet (to the roof) as possible?

once the solar pump pulls vacuum (after 2 minutes) and its running the system flows no problems and heats the pool easily, goes from around 22deg C to about 28deg C in a day in summer.

[paulr33]

i should have checked this earlier, from the vendor manuals of the solar pump;

For pump installations 500mm above water level, it generally requires a foot valve at the pool or check valve in the suction line. Suction lines must be installed below water level until just in front of pump location and vertical riser used to reach pump inlet. AstralPool pumps are rated to a maximum head of 25 meters however refer to your pump’s data plate for actual achievable pressure.

I reckon mine would be 500mm above easy