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

[tenax]

well, with an automated pool vac coming that requires a minimum flow rate to operate ok and changing of furnace, new pipes and wiring change to 220 from 110 to come, i sniffed out a deal on a well rebuilt max-e-pro 1 hp pump on ebay. (my current pump is 3/4 hp and at least 8 yrs old and while working fine, it seemed a bit underpowered for my ballpark total head)

so, here is the situation:

new pump 1 hp going into 1.5 inch pvc throughout the system. if i understand the gpm curve correctly and can simplify, my total head based on the returns length from the main drain and the skimmer are a whopping 108 ft to my pool shed! (combined)

the 3/4 hp starite pump i have when vacuuming using the manual does require the main drain to be closed to add pressure to the skimmer and it seems to do a decent vacuum job.it can get enough suction to hold the vacuum head in one spot sometimes!

looking at the curve again, this pump based on both valves being open would do a measly 20 something gpm. (i don't get any cavitation with current pump unless there is air in the line) but when one valve is closed, it should kick up to about 60 gpm..a bit more than i need a given my sta-rite filter has a max of 62, a little tight..

so, here's my thought for feedback..i plan to use the valves to keep control on the gpm..i.e. simply for example..leave skimmer open, main valve half open..and i think i should be able to find settings that work for vacuuming..and at the same time are safe enough for my filter..i.e. i'm looking for the 45 to 50ish range.

does this seem to make sense? hope so, cause the new 1hp is bought and paid for..by the way, i have to say this was the best deal on the net, fyi. the guy gives a 1 year warranty, has 139 pos evals with no negatives so he must do a darn good job and i was able to buy a pump that goes for 350 plus new at the pool stores for 150 and shipping. (looking at other ones he's sold,they seem to go for between 120 and 180 depending on the brand and size) he says the motor in this is a new A.O. SMITH as well which i've heard is a darn good motor and the whole guts have been refurbished. if it's anything like my current sta-rite that's still going, it'll last a long time.

[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!

[mas985]

The reason you get less pressure in your filter when you close one of the two suction valves, is that you are increasing the suction head and thus reducing flow in the system. Less GPM on the return side means less PSI on your filter guage. If you had a vacuum guage on the suction side, you would see this rise when shutting off the valve. This is why to get an accurate head reading, you need both the filter PSI and suction inches mercury. Calculating total head from just the PSI reading is a very rough estimate and can lead to errors for this type of special situation.

Increasing the head on the return side has a similar effect on the suction (less suction).

The vacuum cleaner should not be an issue as you are going to a stronger pump. You may need to balance the valves so you do not have too much suction on the cleaner.

At 50 feet of head, the new pump will be at about 60 GPM so you will probably be ok. My guess is that your head loss will increase to maybe 55 feet of head because the pump is stronger so you should be under 60 GPM and not need to restrict the flow at all for the filter.

[tenax]

cool mark...i get what you're talking about now..thanks a bunch! good education! ps- that makes good sense re: the vacuum..don't want to suck the liner right off the pool