Could pump 1m above water cause water in basket?

[Webbo]

I am doing a DIY pool install. I have installed a pump 1 metre above water level. Astral 320xt. With an Astral cartridge filter and chlorinator. When pump has been on high speed for a while, the basket is pretty much full of water, bar the a few tiny bubbles whizzing around. On medium speed, there's a fair-sized meniscus-type bubble. And on low speed, water level drops quite a bit.

Is this because I've got the pump up high? Or is there a leak on the suction side?

Thanks

 

[ajw22]

Welcome to TFP.

As long as the pump does not lose prime at low speed I would not worry about an air bubble in the pump basket.

Some VS pumps develop an air bubble at low speeds.

Schedule the pump to run at a higher speed once a day for a few minutes to clear the air bubble.

 

[1poolman1]

I am doing a DIY pool install. I have installed a pump 1 metre above water level. Astral 320xt. With an Astral cartridge filter and chlorinator. When pump has been on high speed for a while, the basket is pretty much full of water, bar the a few tiny bubbles whizzing around. On medium speed, there's a fair-sized meniscus-type bubble. And on low speed, water level drops quite a bit.

Is this because I've got the pump up high? Or is there a leak on the suction side?

Thanks

On the higher speeds the pump can clear the air from the pot. On lower speeds, or if the filter gets very dirty, it can't move the water fast enough to do so. It could happen that, as I've seen with mine, one of these days when you observe it on low the basket will still be full. Not very often, but it can happen.

 

[Webbo]

Welcome to TFP.

As long as the pump does not lose prime at low speed I would not worry about an air bubble in the pump basket.

Some VS pumps develop an air bubble at low speeds.

Schedule the pump to run at a higher speed once a day for a few minutes to clear the air bubble.

Thanks ajw. On low speed it's much more than a bubble - it looks like the water is barely above the intake pipe. When you say "does not lose prime" what do you mean, exactly - do you mean lose water out of the basket altogether?

 

[JoyfulNoise]

The pump, on low speed, doesn’t allow for much total head. By having the pump and equipment 1m above the water surface, you’re adding that much to the total head (suction side head loss + return side head loss). If your suction plumbing is small diameter or long runs with elbows and/or your filter is dirty, then all that contributes to the total head loss. If you have a heater in the return loop, they also add restrictions to the water flow. Eventually, you push the pump outside its operating curve and it will struggle to keep the strainer pot full if not lose prime altogether. Losing prime is when the pump no longer has enough water to keep a constant flow going and then it starts pulling in air. If you run a pump dry for too long, you can damage the seals and eventually destroy the pump.

 

[Webbo]

Thanks Matt. So, basically, I should just run it on medium and high?

 

[Webbo]

Had the pump running on medium all night. This morning it was still running fine but there was an inch of air in the top of the pump basket. And when I released the valve on top of the filter there was a bit of air in there. The pressure gauge says zero, but water is circulating. Does this all sound OK? I know ideally I would have it at pool level, but that's tricky.

 

[Rocket J Squirrel]

The pressure gauge should not read zero when the pump is running. Replace it.

If you find air in the filter often, you have a suction side air leak. You don't want air pressure building up inside the filter; that can eventually explode if too much air builds up.

 

[mas985]

The pump, on low speed, doesn’t allow for much total head. By having the pump and equipment 1m above the water surface, you’re adding that much to the total head (suction side head loss + return side head loss).

As long as the pump is fully primed, the return head gain due to the 1m pump height will offset the head loss due to the 1m pump height so it is a net zero for the total head loss. But again, that is only true if fully primed.

The biggest issue is for priming because that 1m makes it a bit more difficult to prime a pump.