Pool Opening Problems.

[TheGoose]

Ben,

Looking at the 1-HP Whisperflo curve https://www.pentairpartners.com/prod...ctcatalog.aspx I'm trying to figure out what my pump is really pushing.

Taking the fact that I have 20 psi of backpressure, and 1 psi = 2.31 ft of head, then is it safe to assume that I have 46.2 ft of head, or to make it even about 50 ft of total head?

Looking at the chart on pg. 157 and going by the curve represented by "G", which is shown to be the 1-HP whisper-flo (1.65 service factor) it's showing that I should have about 90 GPM of flow.

Taking the low speed chart "B" and considering that I have about 6 psi of backpressure on the system = 13 ft of head. "B" shows at least 40-50 GPM at ~13 ft of head.

Of course I'm not counting head losses from the 2-3 ft of head losses on the suction side so it would be a little bit lower. Also consider that my return piping is 1.5" from the filter to the pool. 90 GPM is way more than the filter is designed for so that would definitely explain why it has never filtered very good.

[TheGoose]

Water is looking slightly better today. FC>5, I turned the pumps off and I'm letting it sit overnight. Tomorrow I'm gonna vac to waste and add sand to the filter.

[mas985]

Taking the fact that I have 20 psi of backpressure, and 1 psi = 2.31 ft of head, then is it safe to assume that I have 46.2 ft of head, or to make it even about 50 ft of total head?

You have to add 3' for the height of the filter gauge above the pump and as you pointed out, there is suction head as well but with 2 suction lines, it should be fairly small so I agree that the flow rate should be at most 90 GPM. Also, low speed is simply half the flow rate of high speed so you really don't need to use the low speed head curve.

[PoolDoc]

Thanks, Mark.

Goose, given that the MAX flow -- for good filtration -- through a 24" filter, like the Tagelus 60, should be 45 GPM or less . . . it's safe to say that you are (1) wasting most of the pumping electricity you are consuming and (2) forcing the filter to fail. If you have 45 GPM on low, you shouldn't even turn the pump onto high, when you backwash.

[TheGoose]

So do you agree with my assessment that I have about ~50 ft of head on the pump and it's probably close to what the pump curve is?

[PoolDoc]

I haven't really checked -- I was just taking what you and Mark said, at face value.

For me to be comfortable estimating your TDH (total dynamic head), I'd want pictures of you skimmer(s), return(s), all equipment connections, pump, filter, valves & piping.

[mas985]

Return head is a know quantity from the filter pressure, ~49' of head. The only unknown is the suction head but as I posted before, that should be minimal because of the dual suction lines. I wouldn't expect more than a couple feet of head IF both lines are kept open all the time. If you want confirmation, I would need more details on the suction lines (diameters, lengths), number suction side valves, and the height of the pump above the pool water level. I can pretty guess the rest and get within 5%.

[PoolDoc]

My bad; should have scanned back for the pictures.

Using the Hazen-Williams calculator here, for the pipe between the pump and the filter (3xL; 1x branchT; 8' pipe => 20' equivalent length), I get a head loss of 9ft at 80gpm and 11ft at 90gpm. Using the Hayward chart I sent you, Mark, I calculate the drop through the dumb-head Tee layout as 3.5ft at 80 gpm and 4ft at 90 gpm. Estimating the equivalents lengths of the 1.5" piping to the pool at 50ft, and splitting flows evenly at 40gpm each and 45gpm each, I find a loss of 6 ft at 80gpm and 8ft at 90gpm

Taking filter pressure at 49ft, I estimate TDH around 57.5 ft @ 80 gpm(9+3.5+6=18.5) and 62 ft @ 90 gpm (11+4+8=23).

also used Charlotte Plastics Design manual