Sand Filter PSI question- new pump a little disappointing

Good day

First some Pool Stats:
12K gal IG vinyl - Old AnthonySylvan "Vacationer"
2 skimmers/main drain
2 pressure side outlets
1.5" plumbing
-uphill climb from the pool to the equipment pad (which is about 30 feet away from the pool)

Old Pump/Filter set up
Hayward SuperPump ¾ HP
Sand Master 19 100# Top Mount Sand Filter

New Pump/Filter set up:
WhisperFlo ¾ HP EE Full-Rated pump
Taglius 60D 325# Top Mount Sand Filter

I just replaced my historically significant SandMaster 19” top mount Sand filter (100#) and Hayward ¾ hp SuperPump with new hardware. I now have a Pentair Whisperflo Full-Rated EE ¾ hp pump feeding a Pentair Taglius 60D Top Mount sand filter (325#).

In my previous set up, my 35gpm (@ 60 ft of head) SuperPump forced the filter to sustain around 12-15 PSI under normal conditions. With the new set up, the WhisperFlo (which is rated at 60 GPM (@ 60 ft of head) is creating a filter pressure of around 8 PSI. – significantly less than what I am accustomed to seeing.

I guess I am curious about opinions on this operating pressure. Is this something I should be concerned about? Is 8 PSI too low for a “High Rate” sand filter? I wonder if I should have gone with a 1 HP Whisperflo. But when I was researching pump/filter configurations, my main concern was the GPM at my given head and the matching max GPM of the Taglius 60D.

I think I am beginning to discover the GPM flow curves are more “academic” or theoretical than I assumed, and that perhaps there is wide range of circumstantial variance within the curves. – Is this true?

When I purchased a pump that was seemingly capable of moving twice the amount of water as my previous pump, I suppose I expected to see a notable increase in the suction rate at the skimmers and main drain. But the rate of suction seems to be disappointingly similar to the rate using the SuperPump.

So I guess my two main questions would be:

Is this PSI normal given the configuration, or should it be higher?

What is your opinion on using a 1 hp instead of a ¾ HP WhisperFlo – would the additional HP create more intake suction, allow for increased operating pressure, but avoid channeling and the other fun stuff associated with oversized pumps? Pros/Cons of a larger pump? Sometimes bigger is not always better, and hearing some opinions of more experienced folks would be beneficial.

As always, thanks for reading.

Peace

I wouldn't worry about the pressure. Sounds fine considering the increased size of the new filter. Theoretically the lower the flow the better for filtration. For a pool your size the pump should be just fine and the filter is oversized but that's OK. There are so many variables in a pools plumbing that an exact calculation is almost impossible and in my opinion those curves are great for general guidelines to get you in the ballpark. Relax and enjoy.
Al

Besides the increase in filter size, another reason for the drop in pressure is that the plumbing on the suction side cannot support high flow rates. The Whisperflow should actually be a stronger pump than what you had before so the flow rates should go up and head loss increase as well (read PSI).

However, since you also changed the filter, the head loss on the return side probably went down thus the lower PSI. Even so, I would have expected with a stronger pump for the PSI to go up or at least stay the same. If you have an abnormally high head loss on the suction side it would also show up as low PSI. The only way to test this is use a vacuum guage on the suction side of the pump. If it is much higher than 10 in-mg, I would say you may have a problem on the suction side.

A few other indicators:

What size plumbing do you have? Suction side of 1.5" would be a problem.

Is your pump unusually loud? Pumps get loud when you have high head loss on the suction side but low head loss on return side.

If you can restrict the flow on the return side, does the pump get quieter?

If you answered yes to the last two, you may have an issue with the suction side plumbing.

I just saw the additional information.

Is the suction side 1.5" plumbing a single line from the pool to pad or from each skimmer/main drain?

One other question is do you see air in the pump basket?

Pump noise is the other indicator of issues.

Hey Mark

Thanks for the observations and questions.

To answer your questions-

-The pump is significantly quieter than the previous pump. It does not sound (smell or feel) like it's working hard at all.
-1.5" pvc plumbing all around
-2 skimmers are combinded into one line near the pool (I dont like this- but its under the concrete deckin, so tough to modify)
and main drain has its own line. - so its two intake lines controlled by a pentair three-way valve at the pad.
-There appears to be a small bit of air in the pump (If you are familiar with the Pentair basket-pot window, the air pocket is about the size of one of the 'pie slices'.) Do you think I am gettting air in through an underground or above ground union on the suction side?

Additonal info: My completely blocking either the skimmer or the main intake via the pentair valve had no appearant impact motor noise, air in the basket, or PSI.

I may try to pressure test the suction end. What would a DIY need to perform this test? If not possible, what would a ball-park cost in NE US be for a pro to come out and perform the test?

Again - thanks for the tips!

My pump at low speed typically runs at 5psi.

Have you checked the obvious--is your sand filter completely full with 325# of sand? When my filter was installed, the bozos were putting in 150# of sand and I caught them and made them add the extra 50# because it is a 200# filter. Too little sand is not good. Are you sure they used filter sand and not sand-blast sand (which is cheaper)?

Also a lateral in the filter could have been damaged by the installer--if sand gets in the pool, that's a clear sign.

I almost think you should empty your filter and install 325# of filter sand yourself, see if that fixes it. Watch the sales: Filter sand can be had for $5 for 50#--$35 to replace your sand.

If the sand is OK, you can also use Pocono's DE trick to both better your filtering AND increase your pressure. It's cheap and those of us who use it think it works really well.

Also, as your filter sand ages, it should get dirtier and increase pressure--and filter better.

Just some ideas to check. I sure lots of folks have other ideas, too

Your numbers look normal to me. I'm running a 1.5 HP uprated pump on a 300# sand filter and get about 17-18 psi when the filter is freshly backwashed. My pump is oversized for the filter (or the filter is undersized, probably the latter). Your pump may be a bit undersized but that's a much better situation than mine.

What's the flow rate of you setup? What's the turnover time for you pool? I'll bet both are just fine and if so, you should be getting great filtering with this setup. If you want to "polish" the water even more, take Carl's suggestion to add a bit of DE.

I would have expected the PSI to drop if you closed off the skimmer or main drain. It sounds as though maybe your new filter PSI guage is not working properly. This is a fairly common problem although not so much for new filters.

Just to confirm, you did not see PSI change with either main drain or skimmer but did you set the valve for both main drain and skimmer on? Any change there? Have you checked to see if there is any blockage in the lines. You can backflush the lines with a hose and a rag (to seal) or get yourself a Drainking.

Also, about how high is the pad above the pool? Although this does not add to the total head loss, elevation will increase the suction head and decrease the return head relative to no elevation.

1.5" plumbing is really too small for the suction side and could be primary cause to the air in basket and low PSI reading. Even though you new pump is only 3/4 HP, it is still a very strong pump and possibly too strong for your plumbing. The pump cannot draw enough water so it is drawing air through the seals in the pump lid or valves. A larger pump would only make this worse so don't go that route. However, a two speed pump would allow you to run at the low speed most of the time which your plumbing could easily handle.

If you want to go to the trouble of measuring the suction on the pump, you just need a vacuum guage, Sears has one for $20, and get an adapter so that it can screw into the pump's drain plug at the bottom of the basket. But this will only confirm that your suction head is very high and not really tell you why.