Low flow pumps - Is Air in Solar system ok?

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Mark,

oh right. The head loss before the pump... forgot about that. The suction is a 50 running 5 meters and a 40 running 3 meters.

Re. 78lpm at 3.5m head, are you calculating head based on revised flow rate?


For measuring flow speed, I might splice in a remaining section of clear pipe I have, and just time the speed of bubbles.
 
The water level is about half way down the U. About 200 above bottom of U. Sometimes slightly lower. Not sure why it isn’t exactly the same always.

but generally about 300 below gauge, so more like 1.5m
head (including the 12kpa), as opposed to 1.4m

This is all approximate. The gauge isn’t exactly a scientific device!
 
mas985 said:
I think I messed up some of the numbers. What was the air/water level relative to the U bottom?
Click to expand...
This is fun and I still want to know how far in mm the water pushes up the solar pipe from the top of the return line when the solar system is open to atmosphere and the system is running at the new low speed and solar is off, drained and everything is running in a stable condition. Also the kPa at the filter pressure gauge same conditions
 
tomfrh said:
The water level is about half way down the U. About 200 above bottom of U. Sometimes slightly lower. Not sure why it isn’t exactly the same always.

but generally about 300 below gauge, so more like 1.5m
head (including the 12kpa), as opposed to 1.4m
Click to expand...
Ok so if there is 1.5m of dynamic head, then the flow rate through that section of plumbing would need to be about 110 LPM. Looking at the pump's head curve, that is about 2.75 m of total head loss. The head loss from the TEE to the pool would be 0.7 m (0.5 + 0.2) of head. So that means the other part of the plumbing, suction and short section between pump and filter would be about 0.55m of head which sounds about right relative to the return side.
 
No worries, I do know and understand the incremental increase of each 50 RPM. I think you've mentioned it three times, lol.

When your pump is running at your newly defined low speed, with solar off, system stabilised, I'd like to know the pressure at the filter, and the pressure at the solar tee (but because you have no gauge there, I'm asking for just the amount the water rises in the solar pipes when the pump comes on, in mm) including all 1500 RPM.

But honestly, it's no big deal. Don't worry about it. It's just a curiosity relative to another project I'm working on.

By the way, I really appreciate how much info you're providing, which helps others solve problems as well.
 
Pressure is around 15-20kPa, water is around 100 below the T. I'm not sure what you mean by "amount the water rises" when the pump comes on. Rises from what? Sometimes it's lower to start with, sometimes higher, depending on how much glugged out when it was off, and residiual pressure and water elsewhere in the system - eg in the solar tubes.
 
Re. flow rates, I measured the flow rate in the tubes with solar off. Measured by looking at bubbles in the clear section of tube.

At 1400 rpm flow rate is ~105 lpm. Chart says 3.1m head

At 1600rpm the flow rate is ~150lpm. Chart says 3.5m head

I think I'll run it at 1600rpm from now on. It seems a little happier that way.
 
Good to hear it's all solved. Thanks again for providing all the details.

This thread is a good heads-up. Some things that are routine for a single speed pump work differently with a VS pump, and a VS pump at low speed mightn't do everything the old pump did without some adjustments or controls. Good for people to know.
 

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I set mine at 31 and it ran about 4 hours today. Seems warm enough to most everyone who swims here at our place. I have 60% coverage which is also a bit low, but it's all I have to work with because of solar PV on the main roof. About all you could do to get more heat is speed up the flow a bit and see it you can get the differential down to 1 or 1.5 degrees. Or add more roof area if that's possible. But hey, as long as people are jumping in and enjoying it...
 
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