Figuring static head adjustments to dynamic head

SPP

LifeTime Supporter
Apr 6, 2008
306
Indonesia
Now I am confused.....TDH, Hydraulic 101

Hello Jason,

GazzMan question got me thinking.

I know this sounds paranoid, but may I ask if I am reading my filter pressure wrong in respect to TDH discharge side ?

A filter located above a pump by 8.25 feet , as long as the water flows back to the pool ( minus 8.25 feet ) is not to be calculated as head loss. This is what I read in hydraulic 101.

My question is :

01. The filter pressure gauge is located on top of the sand filter selector valves, which is 8.25 feet above the pump impeller center. Is it correct to say that my pressure gauge is not reading the head loss of 8.25 feet, but instead it will read ONLY filter clogging pressure build up and whatever water friction loss due to the 100 feet of plumbing after the discharge port of the sand filter.....but, since there is a downhill syphoon effect due to 8.25 feet elevation of the filter location in respect to pool water surface....I am actually getting "X" psi reduced by 3.5psi ( 8.25 divided by 2.31 = 3.5 psi ) ?? In other words, for purpose of calculating total head loss on discharge side of the pump, whatever I read on the filter, I must add 3.5 psi. Or, I must put a pressure gauge closest to pump as possible, if I want to know total head loss on discharge side of the pump.

02. Since my pump impeller center is actually 2 feet above pool water surface and that filter is 8.25 feet above pump impeller, the real height the water flows down with the help of gravity from the filter discharge port is 10.25 feet or I must add 4.4 psi to whatever my filter pressure gauge is reading, if I want to know total discharge head loss calculated from pump port.

Did I calculate correctly ?


Many thanks guys...

SPP
 

JasonLion

TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
37,879
Silver Spring, MD
You are on the right track. Keep in mind that you are working from a "rule of thumb" estimating approach. Doing the complete calculation is noticeably more complex. You need to be careful which of the "real" factors you bring into play, because you don't want to duplicate something that is already factored into the rule of thumb. That said, the usual estimate assumes that the pump and the filter are closer to each other and that they aren't as high above the pool, but it does assume that they are a little above the pool.
 

SPP

LifeTime Supporter
Apr 6, 2008
306
Indonesia
Thanks Jason.
I am was looking into this because my head loss from pipes length alone was supposedly to be approx 15 feet acording to on line calculator but looking at my filter pressure, I am getting lower PSI than expected. So I was thinking , where did I go wrong ?

I know accurate calculation is too complex, but at least I know now that I have 10.25 feet of gravity value that I missed.

I will try to install a press gauge as close as possible to the pump to verify the calculation.
When the vacuum gauge is installed, I can further verify my pump curve accuracy.
I am still not able to get my pump actual spec which is 50hz instead of USA 60hz spec that Hayward website has.
Usually 50hz model pump get derated by 10% if everything being the same and base design is 60Hz

This is fun !!!!!
Thanks again...