new max-e-pro sta-rite pump & operating questions

[duraleigh]

Tenax,

I am somewhat suspicious of your head calculation.....it seems quite high.

Mark (mas985) is the guru and I'll bet he sees your post and replies. He has a "rough" formula you can use to get pretty close on head.....I'm gonna' make a stab at remembering it.....I disavow all responsibility for getting it right!

Take filter pressure x 2.13 and add 10 for the suction side resistance. So, assuming I've got that right, your filter pressure would be 46psi.....I don't think a pool pump can get there.

In any event, I am clearly not a good resource for a definitive answer. Others will hopefully bail me out soon.

[tenax]

if you are referring to my 108, i searched the net trying to find a calculation that wouldn't involve measuring vacuum and such..i know it's ballpark for sure, but i got that suggestion from inyopools faq i believe it was that said for a "simple" TH calculation, add the length of all your returns to get the TH. then i went to the "curve"...maybe garbage in, garbage out at least as far as the TH, but i don't know how to derive it any other way that i "get".

a summary and more information if it helps includes:

15,600 gallon pool (u.s.)
a skimmer and a main drain.
1.5 inch piping everywhere.
1 hp sta-rite max-e-pro pump which i believe is supposed to develop in excess of 60gpm at TH of 50.
sta-rite sand filter max rated 62gpm
vacuum that requires a 1hp or 1600 gallons per minute flow, i believe it is.
4 -90 degree bends, 3-45 degree curves in the pump shed. (don't know how it was bent underground as the pool already existed)

[duraleigh]

Head loss is usually between 45-65 ft of head which means your flow is between 110-135 GPM. Your probably near the lower end given the size of the pump (higher head). If you want a better estimate then you need a more accurate head measurement.

Total Head = Return Head + Suction Head
Return Head = 2.31 * Filter PSI
Suction Head = 1.13 * Pump Suction (in. mg.)

If you can't measure suction head which requires a vacuum guage, use this formula:

Total Head = 3.2 * Filter PSI (assumes suction is 40% of return head)

I found Mark's post. So, if you take his simplified calc and use 108 as total head (108 / 3.2 = 33.75) your filter pressure (clean) would be around 33-35. Is it that high?

[tenax]

do you mean as measured by the sand filter pressure guage? i run about 15, 16 normally with the 3/4 pump since the day i started..when it's up to 20, it's definitely backwash time.

[tenax]

it did occur to me when figuring that 108 number that maybe i was supposed to take half of that? if i use 54 and do the division, it comes to 16 and change which is exactly what my pressure guage says on the filter.

[mas985]

Tenax,

The problem is pipe length is not equivalent to head loss although they are related. There are rules of thumb but I would not recommend calculating head loss from the plumbing design as this is very difficult to do and not always very accurate. The easiest and most accurate method is to calculate it from your existing filter pressure.

Based upon your filter pressure of 16 PSI, you are currently at about 50 feet of head which is fairly typical.

Is the new pump a full rated or up rated 1 HP? A 1 HP uprated pump is the same as a 3/4 HP full rate pump so the one you got may be ok or close enough.

Also, you will have more GPM with your valves open than you will with them closed. You mention closing valves to control GPM but why would you want to do that? Filter limits? If so, I would not try to adjust GPM on the suction side as this usually causes cavitation or air leaks. It is best to control GPM on the return side if possible. Pumps perform better this way.

[tenax]

the current 3/4 hp is actually a 1/2 hp uprated..the new one will be a 3/4 hp uprated to 1 hp.

maybe i'm not explaining myself properly on the valves thing..here's what i know...when i have both ball valves open on the 2 lines labelled skimmer and main (lines that come in from the ground as 2 separate lines into 2 separate valves, then into a T and then into the pump intake i guess you'd call it) i get less pressure in my filter when i have one or the other closed..but note that if i have the skimmer valve open but the main drain line closed, there is more velocity in the skimmer..if i reach my hand in, there is definitely more suction in the skimmer.

so, back to the original question about the new vacuum and should i have enough gpm flow. or maybe i'm making an assumption that extra suction is higher flow rate..my brain hurts now

it sounds like i wont' have a concern otherwise relative to to much pressure for the filter (which is rated for 62 gpm max) with the new pump!