Low flow pumps - Is Air in Solar system ok?

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I waited for hours with solar off. I’m sure of that. Endless bubbling. The air in the solar return pipe stayed at the T junction forever and the water flowing thru the T kept capturing air.


i cannot say for sure how long I waited with solar on. In retrospect I should have done a long test with solar on and monitored more carefully. Perhaps it would have eventually purged all the air.

in any case, with solar off, it bubbles permanently without the trap, and doesn’t bubble with the trap.
 
OK, I hear ya, Mark. There's a wee bit of head loss in the 2 feet of main return line pipe from the solar inlet to the solar outlet, which causes (let's say) 1 inch of head loss. And that creates the opportunity for water to head on up the solar inlet when it's shut down, creating the positive pressure at the end of the solar outlet relative to the pressure in the main return line. And that burps out a bubble. Makes sense.
 
I think the system is simply trying to drain via the solar return tube. There's not enough pump pressure to drive the water up above the T, there's a slight vacuum, which the U is isolating.

If I up the RPMs slightly it'll push the water level above the T, meaning the trap isn't needed.
 
On another topic...

It's fair to mention that the solar pump should be tested on it's own. Usually they will starve of water if the main pump is not on, but yours may not. It might just flow enough to keep some water moving through the system (but without filling and being optimum maybe, who knows, i.e. just like your original state). If the solar pump does move water on it's own, ignore the rest of this post.

If water doesn't keep flowing when solar pump runs on its own, you have a choice. If the main pump screws up when you're away, the solar pump may try to run, and could burn out. That's a $250ish >=2 go'fer trips, risk. You can add a flow switch that detects flow from the main pump, and use that to protect your solar pump. But the cost, time, place to put it, might not be worth protecting a $250ish risk, that's a personal decision.

The hack, which I don't recommend, is to piggyback the solar controller off the SWG, so it can only run if the SWG is powering the main pump. You have to be sure that the rating on the SWG pump outlet (and whatever dual adapter you use) is enough for both pumps. The downside, and why I wouldn't do it, is that some people on Whirlpool forum have reported electrical 'noise' issues causing funky things to happen on variable speed pumps and chlorinators, and I'm guessing adding a second pump would increase the chance of electrical noise. The problems have just been things like: pump doesn't remember non-default settings; chlorinator needs timers reset; electronic things, solved with a reset and re-programming, so they're not catastrophes, but would be a definite pain if it happened each time stuff runs.

Personally, and subject to hearing more from others here, I would just risk the solar pump, because the SWG failure is unlikely, and the dollar value isn't very high compared to an SWG power supply or the VS pump. I would be shopping for a flow switch in the meantime, and/or it could be added to your benefits side of converting to one pump.
 
5 or 10 minutes won't kill it, and it does take a while to pull water, especially through a pump and filter! But I wouldn't go much beyond that, and I'd quit if anything seemed to be warming up fast.

I'm also curious about something. After everything has been off for an hour or two, is your pump strainer basket drained down about 2/3rds of the way inside it?
 
Re:  Low flow pumps - Is Air in Solar system ok?

tomfrh said:
I installed the Valve and the U trap. The solar return U-trap extends about 400mm below the horizontal main return, and connects to it from the underside.
Click to expand...

tomfrh said:
the U is preventing air in the solar return from getting into the main line. The water level in the solar return side of the U sits about 200mm below the T. The air which previously fed straight into the T from above cannot get down around the U.
Click to expand...

I know I read these but I guess it just didn't register so I went back reread everything and now I think I understand what you are saying.

This is a 0.4 meter deep U correct? That is not an insignificant elevation change.

So where does the bottom of the U sit relative to the filter gauge? The horizontal pipe you spoke of going to the pool must be above the filter? The filter is at 12 kpa which is a positive 1.2 meters of head so either there is a lot of head loss between the filter and the tee or the tee was fairly high above the filter.

How high is the pump above the water level?
 
I understand the trap to be above water level, and 0.4 metres, Mark.

Also, at the time of the 12kpa comment, the main thing was that there was positive pressure, and there was a lot going on, so I didn't follow it up. Normal pool system pressures run roughly 20 to 140 kpa (3 to 20 PSI, 2 to 14 metres head), so I did wonder at the time if maybe there's two scales/units on the pressure gauge.
 
Yes I had a decimal point moved (fixed). Thanks. 12 kpa would be reasonable for low speed if the filter was elevated enough.
 

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Ill measure the heights when I get home, but approximately the pump is about 300mm above water. T about 700mm above water. T is level
with gauge. Bottom of U about 400-500 below T and gauge.

SWG is after the T and trap, and is approx 300 above the T.
 
I measured it properly:

pump inlet 350 above water
Gauge 1000 above water
T 900 above water
bottom of U 500 above water
SWG cell 1150 above water

Between filter and T there is:

1500mm of pipe total
2x 90s
1x 45
1x T which goes to solar pump
1x jandy check valve


ive also tried adjusting the filter speed. Every increment changes speed by 50rpm, changes gauge pressure by about ~3kPa, and changes water level in solar return pipe by about 40mm
 
So between the filter gauge and the U, there is 1.4 m of head loss. At such a low flow rate and given the plumbing, that seems quite excessive. When was the last time you backwashed the filter? Is there anything wrong with the check valve?
 
Filter has been backwashed recently. The check valve is opening.

Why do you think 1.4m is excessive?

Water is flowing at ~150lpm. Head loss of 1.4m doesn't seem unreasonable to me. The water has to flow thru a filter, pipe, fittings - plus there's the pressure loss due to venturi effect.
 
Ok, but how did you get 2 meter of head loss?

2 meters of head loss at 150 lpm is very low head loss for a pool. This is about 1/2 the head loss of a typical pool with 2" plumbing.

Also, you would not lose 1.4m out of 2m in just that short section of plumbing. That would only be about 1/4th of the total head loss.
 
Wouldn't the difference being discussed include the head loss through the filter media?

By the way, I'm curious. When you're running on your new low speed, with solar off, can you tell how many mils the water is pushing up the solar pipes? (i.e. top of water down to top of main return pipe), and also the new kpa on the filter gauge.

I'm not sure on this, Mark, but is the water traveling in the return line through the T exerting a small negative pressure on the static inlet of the T, by venturi effect?

- - - Updated - - -

FWIW, my system on 100 LPM is around 3-4 PSI when the filter is clean, so about 2 to 3 metres head loss. At 150 it's more like 8-9 PSI, 6 metres.
 

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