#### SPP

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
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.