Are two filters better than one?

[Aranon]

I have two filters. I have A Dynaflo 1 Hp two-speed pump hooked up to a Hayward 300 lb. sand filter with 300 lbs of filter sand from Leslie's, and then it goes to a Pentair 150 cartridge filter and then to the pool. Even on low speed right back to the pool I have tremendous flow.

I have it hooked up to ten 2' x 20' solar panels on top of our two story house and on high speed it has great pressure. You can see the water current going way out toward the middle of the pool. On low speed, it does not have enough pressure to to go up two stories, but it didn't when I had it only hooked up to the cartridge filter. I leave it on low speed during the night and high speed when I am using the solar panels.

I bought the Hayward S224T used on ebay for $ 124 including freight. It looks brand new. I plumbed everything with 1 1/2" PVC. It works great.
My pool is crystal clear.

Aranon

[duraleigh]

Aranon,

On low speed, it does not have enough pressure to to go up two stories, but it didn't when I had it only hooked up to the cartridge filter.

Once your system is primed, the vertical height of any part of your system, including solar panels, is irrelevant to the pump. It will circulate thru the panels just fine on low speed.

[Aranon]

I can have the pump on high and everything is going good and I got lots of pressure and everything. The water is going up through the 1 1/2 PVC to the second story flat roof and I got warm water returning, but when I switch the pump to low speed nothing changes for about a min or so and then the water stops flowing. I waited for about five min to see what would happen and nothing. Everything is running, but no water is returning back to my pool.

I switch back to high speed and in about 30 seconds the water comes back on. Tried this several times and same effect every time. My only conclusion is that on low speed the pump does not have enough power to push the water up that high and through 10 solar panels. If you got any solutions, I am up for them. When I had the solar panels on the ground just trying them out it worked on low speed and the water seemed to come out hotter.

I keep wrestling in my mind would it be better to have low speed and hotter water but less flow, or high speed with warm water but more flow. On one had I look at this that yeah, the water is hotter at low speed but I am not putting much water in the pool at a time so it is not really doing much. ( Its a big pool, 18' x 40' oval by 54" high) On the other hand I am adding large volumes of water at higher pressure that is putting in a little cooler water but lots of it and shooting it out really far toward the middle. My thinking is that the water turnover rate is going to be greater at high speed and should bring the temperature up quicker at higher volume and pressure than hotter water at low pressure, and low volume. Sort of like which is going to heat you bath tub up quicker if you start with a tub full of cold water, a small trickle of hot water coming in at 100 degrees or a large full blast volume of 90 degree water. The difference between the low speed (when it was working on the ground was 10 to 11 degrees difference) Right now my water at high speed is coming out at around 90-92 degrees from the solar panels.

Pleased advise how the pump should operate fine on low speed going up 2 stories. From what I gather low speed is 1/3 hp and high speed is 1 hp.

Thanks
Aranon

[duraleigh]

Hi, Aranon,

First off, I'm not sure there is any advantage in operating the panels at low speed. I think you would have to do some engineering calculations to decide how you get the most bang for your buck. My thought would be that on a really solar intense day, hi speed would be best and then, maybe on a cloudy to partly cloudy day it may be more efficient on low. That would be noticeably above my ability to calculate that but the slide rule dudes can do it.

Now, to your question. The short answer is that no matter how high the column of water is, the energy required to push up that water is equally offset by the column of water pulling down and returning to the pool on the outflow. In essence, you work against gravity going up but then gravity returns the favor by pulling down with an equal force on the descending water. That said, there can be virtually no air in the lines for that to work.

As to why that will not work for you I'm not sure. There is, of course, a little more friction from the increased length of PVC pipe (and, possibly lack of capacity) but the end result would only be a diminished but stable flow. Perhaps others will see this post and have experienced the same problem.

[Aranon]

Thats exactly what I thought. If I could get the water up and back down then it shouldn't take much to keep it going since the water going down should act like some sort of siphon effect pulling the water down and to a small part up too. But that does not seem to be the case. The strange part is that I have great pressure for about a min to a min and a half after I switch the pump to low speed and then it slows down to nothing. I don't know whats going on. Got the pool up to 85 degrees. All we want it up to is 88 degrees so I don't think we are going to have a problem, but it's got me stumped. I have read on other post that low speed pumps will not carry the water up to the roof and I am going up two stories. Any help would be greatly appreciated. Thanks.
Aranon

[duraleigh]

Aranon,

You might send a PM to mas985. He is excellent at calculating Total Dynamic Head and it IS possible that those ten solar panels offer so much resistance that your pump can't overcome it on low. If that's the case, you would have the same result if the panels were at pool level or even in the basement.

[Aranon]

The panels worked fine on the ground at low speed