Pentair VS SuperFlo pump run at a constant RPM pumps less water as time goes on.

[EdLaFave]

I just got a brand new Pentair VS SuperFlo pump. I'd like to have my pump running 24/7 at the lowest speed required to turnover the pool. This is what I'm observing:

• I set my valves to be in pool mode only (no spa),
• I programmed the SuperFlo to run at a single low RPM all day long, I'm not using the other two time slots.
• I manually started up the pump at a high speed and waited for some air in the basket/system to flush out of the pool jets.
• I switched over to the first (and only used) setting and got it running at a low RPM.
• I used my hand to gauge the amount of water coming out of the pool jets.
• I came back 12 hours later to gauge the amount of water coming out of the pool jets and it was significantly less. I noticed that there was once again some air (maybe an 1/8 of an inch tops) accumulating against the top/concave portion of the lid on my basket, although there was still water touching the lower part of the lid, so there isn't too much air.
• If I quickly ramp up the RPMs to flush the air out and go back to the lower speed, then I once again feel the correct amount of water coming out of the pool jets.

If I do this same exact test with both the pool jets and the spa jets open then everything will run fine initially and over time no water will be pumped through the spa jets. In fact, water will actually drain from the spa to the pool. Likewise, the water pumped through the pool jets also diminishes.

My hypothesis is that I've got an air leak somewhere in the system, I guess on the suction side (since I'm seeing air in the basket)? And as more and more air is accumulated it somehow increases the resistance in the system and causes the pump to push less water?

What's going on? How should I address this?

 

[Jimrahbe]

Ed,

The slower you run, the more likely that you will get air under the pump lid. It does not take much of a small air leak to allow that to happen.

The first place to check is the o-ring under the pump lid.

The simplest thing to do is program the pump to ramp up the speed for half an hour a couple of times a day.

You do not say what speed you are running, but I would not run less than about 1,000 RPM.

And... just so that you know.. It is a myth that you must turnover X amount of pool water each day to prevent algae.. It is just not true..

Thanks,

Jim R.

 

[EdLaFave]

Is my hypothesis possibly correct, that air slowly building up on the suction side can cause the flow rate to slowly decrease? If that's not possible then maybe I need to replace the pump or look into something else? If that is possible then maybe I can find the air leak and maintain constant flow?

The first place to check is the o-ring under the pump lid.

The pump is brand new so the o-ring under the pump lid should be fine, but I did check it and it looks good.

The simplest thing to do is program the pump to ramp up the speed for half an hour a couple of times a day.

Unfortunately the SuperFlo only let's you schedule 3 settings per day (i.e. 2 changes per day), which means that I can only schedule one ramp up per day. I have been using that to clear the air bubbles, but the infrequency of doing that means the pump is still pumping a decreased amount of water most of the time.

You do not say what speed you are running, but I would not run less than about 1,000 RPM.

I've observed this behavior at various speeds ranging from 400-1,000 RPMs. I'm not sure how high I can get the RPMs and still see this behavior.

Why wouldn't you run it less than 1k RPMs? I estimate that running it around 460 is enough to turnover my pool once per day.

And... just so that you know.. It is a myth that you must turnover X amount of pool water each day to prevent algae.. It is just not true..

Can you explain and provide supporting links?

 

[jerryt]

Try upping the RPM a little until the final flow after a few hours is what you want (Electronic hot or cold).

 

[EdLaFave]

Try upping the RPM a little until the final flow after a few hours is what you want (Electronic hot or cold).

Of course I could do that, but that just sidesteps the problem. I'd like to fix this problem. I'd like to be able to fix the decreasing flow over time and avoid wasting money by turning over my pool more often than is necessary.

I'm also wanting to know, can a slow air leak on the suction side cause the flow rate to drop even as the RPMs on the pump are constant? For all I know they're unrelated and I need to return a defective pump?

 

[jerryt]

My opinion is it is just the rate that the pump can call that RPM. Say 750 RPM, the controller will accept 725 to 775, which changes by temperature. this is all my theory.

 

[EdLaFave]

My opinion is it is just the rate that the pump can call that RPM. Say 750 RPM, the controller will accept 725 to 775, which changes by temperature. this is all my theory.

I don't understand what you're suggesting.

It almost sounds like you're saying the RPM I enter into my pump isn't the exact RPM it runs at. I don't know why that would be the case, but if I entered 775 and it actually ran at 750, I don't know why that would cause the flow to do diminish over time. The folks at Pentair said if you set the RPM to one value, it will not fluctuate, it'll stay at that value.

Or it sounds like you're saying that my pump runs at different RPMs based on its temperature? If this is true on some level, I don't think it is causing my problem. When the flow rate is diminished, I can run it on a high temperature for a minute, pump out all the air, and switching to the low temperature will immediately return me to the "right" flow. I don't think cycling the pump through 1 minute of high rpms does much to change the temperature. I've also seen the "right" flow in early morning with low temps and the "wrong" flow in afternoon with high temps and vice versa.

 

[Jimrahbe]

Ed,

Part of the problem is when running at low RPM, the pump lid does not get sucked down against the gasket as well.. Having air under the pump lid is normal for VS pumps running at low RPMs.

In the big picture you don't save very much running lower than 1,000... You do save a little, but for me not worth the problems. I can run my pump 24/7 at 1200 RPM for less than $20 bucks a month.. Could I save an additional $10 bucks, maybe, it is just worth it to me.

See this link.. Determine Pump Run Time - Trouble Free Pool

Pool filters are designed to capture the stuff that falls into your pool, not to prevent you from getting algae. Algae is a chemical issue and not a filter issue. I am not saying you can't run 10 x turnovers a day, if that is what you want to do.. I'm just saying it is not a requirement to have a clean and sanitized pool..

Thanks,

Jim R.

 

[EdLaFave]

Pool filters are designed to capture the stuff that falls into your pool, not to prevent you from getting algae.

So the pump is only useful for removing debris that falls into the pump (I have a screened in enclosure so that is an incredibly minor concern for me)? So when people tell me the circulation created by the pump is necessary to mix everything in with the chemicals, they're just wrong?

when running at low RPM, the pump lid does not get sucked down against the gasket as well.. Having air under the pump lid is normal for VS pumps running at low RPMs

That's interesting. I suppose that would make sense. If the suction is minimal then the seal wouldn't be as strong.

 

[jerryt]

My intellifo running at a set GPM, varies in watts throughout the day. There are tolerances in what the pump accepts for a setting. Do you have a flowmeter?

You are stating the flow rate is changing but not the RPM setting, so Pentair must be telling you wrong, that 775 is always 775.. I has not worked that way for me with both intellifle VF and VS pumps, they operate in a range, not at specific setting, They stay close 5 to 10%

 

[EdLaFave]

My intellifo running at a set GPM, varies in watts throughout the day.

Well if yours allows you to set GPM and various conditions (like air build up) can increase resistance and thus decrease flow, then I'd expect your pump to increase/decrease RPMs throughout the day.

Mine only allows me to set the RPMs.

Do you have a flowmeter?

No. My claim that the flow rate decreases over time is based on me putting my hand in front of a jet when it starts and doing the same a few hours later.

You are stating the flow rate is changing but not the RPM setting, so Pentair must be telling you wrong,

Well they aren't necessarily wrong. If the air build up can produce more resistance then you'd expect flow to drop as resistance builds up. I just don't know if air build up increases resistance (or something else may increase resistance).

 

[sean.a.hyde]

Well if yours allows you to set GPM and various conditions (like air build up) can increase resistance and thus decrease flow, then I'd expect your pump to increase/decrease RPMs throughout the day.

Mine only allows me to set the RPMs.

No. My claim that the flow rate decreases over time is based on me putting my hand in front of a jet when it starts and doing the same a few hours later.

Well they aren't necessarily wrong. If the air build up can produce more resistance then you'd expect flow to drop as resistance builds up. I just don't know if air build up increases resistance (or something else may increase resistance).

The "you need to run your pump a lot to mix stuff" take doesn't hold up well when people keep their pool in good shape when their pump dies by stirring for a few minutes throughout the day.

Have you looked at your power readings on the SuperFlo? I found very diminishing returns to lowering the RPMs below 1200 as far as $$ savings. You'd probably save more money by simply running the pump less often.

My go-to suction-side leak detector is shaving cream. Spray it around every joint and fitting on the suction side while the pump is running. Look for tiny holes to appear.

I think it is important to note that the RPM setting on the SuperFlo seems to be a "set RPM" not an "actual RPM". This is most obvious when you change it (manually or due to a schedule change) -- the motor RPM lags the display. So although the set RPM is 750, the actual won't be exactly that. The tighter you make that control loop, the harder it is on the electronics -- especially when inertia is involved (both the impeller and the water). If I was designing a pump controller, I'd make the control loop very loose because I didn't need 750.000 RPM, just something close.
That said, I don't think the control loop variation would be felt at the return.