Filter sucks air in at low rpm?

[BDY]

I noticed today something unusual about my filter but since I’m so new I this I don’t know if it’s an issue or normal. I have an intelliflo 3HP 011056 pump and a CCP520 filter on my 9000 gallon pool. I run the pump 24/7 at 200 rpm above where my IC40 has a flow issue, with 2 hours a day set at higher rpm for skimming.

Case 1:
900 RPM
<2 psi (too low to read on gauge)
19 GPM

Case 2:
2700 RPM
9 psi (right where it was when PB started up pool)
79 GPM

When the pump is running low rpm a little bit of air builds up in the pump (maybe a few half dollars worth) which goes away when the pump spins up to higher rpm. I never thought anything of it.

But today I was thinking of opening the filter to clean out any leftover junk from construction and when i opened the reliefs valve at low rpm, air enters the filter via a gentle sucking sound and vacuum feel to the relief valve. At high rpm, water comes out. Is that normal for air to enter the filter when pump is running really low? Does that imply a negative pressure? Or just not enough flow from pump to fill the filter?

Something to worry about or just keep on learning about my pool?

Thanks
B

 

[PoolStored]

I noticed today something unusual about my filter but since I’m so new I this I don’t know if it’s an issue or normal. I have an intelliflo 3HP 011056 pump and a CCP520 filter on my 9000 gallon pool. I run the pump 24/7 at 200 rpm above where my IC40 has a flow issue, with 2 hours a day set at higher rpm for skimming.

Case 1:
900 RPM
<2 psi (too low to read on gauge)
19 GPM

Case 2:
2700 RPM
9 psi (right where it was when PB started up pool)
79 GPM

When the pump is running low rpm a little bit of air builds up in the pump (maybe a few half dollars worth) which goes away when the pump spins up to higher rpm. I never thought anything of it.

But today I was thinking of opening the filter to clean out any leftover junk from construction and when i opened the reliefs valve at low rpm, air enters the filter via a gentle sucking sound and vacuum feel to the relief valve. At high rpm, water comes out. Is that normal for air to enter the filter when pump is running really low? Does that imply a negative pressure? Or just not enough flow from pump to fill the filter?

Something to worry about or just keep on learning about my pool?

Thanks
B

Funny. Lots of thread on this issue over the years, including a long thread I created on tis issue. Running VSP at low speed, even if you lubricate o-rings really well, the pump gets a slow suction side "pancake of air" that can lead to what we have called a "silver dollars" worth of air. A short cycle of high RPM clears it. Not sure we have figured it out, but I now run 24/7 at 1400 RPM, with 15 minutes at 3000RPM each 24 hours, which clears the bubble. Best guess is it is, at low level RPM creates air leak around pump cover at low RPM.

 

[BDY]

Thank you
I was expecting that - I wasn’t expecting the filter relief valve to work in reverse at low rpm and suck air in rather than send water out. Is that part of the same issue?

B

 

[PoolStored]

Thank you
I was expecting that - I wasn’t expecting the filter relief valve to work in reverse at low rpm and suck air in rather than send water out. Is that part of the same issue?

B

I'm not sure we are using the same language. A suction side leak would be from suction valves, connections, pump drains, pump cover or pump drive seal. Once you get beyond pump shaft seal it is pressure side leak and would show as water leaking.

Air in the pump basket cover would only be suction side. A leak in the filter relief would be pressure side and show water leak as a result.

 

[BDY]

Sorry, I think my post was confusing as I had two questions that I thought were related but sounds like they aren’t.

The first question was the air in pump (thank you for the good explanation).

The second question was why when i open the filter relief valve at low rpm the air sucks into the filter rather than water coming out. This doesn’t happen at higher rpm and I was wondering if it’s an issue esp as the pressure gauge is effectively zero at the low rpm (needle resting on peg).

B

 

[PoolStored]

Sorry, I think my post was confusing as I had two questions that I thought were related but sounds like they aren’t.

The first question was the air in pump (thank you for the good explanation).

The second question was why when i open the filter relief valve at low rpm the air sucks into the filter rather than water coming out. This doesn’t happen at higher rpm and I was wondering if it’s an issue esp as the pressure gauge is effectively zero at the low rpm (needle resting on peg).

B

Cool. Let's break this down.

First, is your gauge at zero with everything off? If not, replace it.

Second, run your pump, high RPM, open air relief on the filter until the air is expelled. Then run in normally.

Do you have a VSP? To help us, it would be valuable to fill out your signature...

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[BDY]

Gauge is at zero with everything off. 0-1 psi at 900 rpm, 9 psi at 2700 rpm. At both low and high rpm the water is flowing out of all 6 returns.

Running at high rpm, the air leaves the filter and water comes out (like it should).

Running at low rpm, the air is sucked into the filter and no water comes out.

I have an Intelliflo VSP (011056).

It should be visible in my signature already - I just double checked and the signature was showing for me… can you see it?

Thanks
B

 

[Rocket J Squirrel]

I think your 900 RPM is simply too low to properly pressurize your filter and water is just drifting through. You want enough force in there to fill the filter tank to the top and engage the full height of the cartridge(s). You should not feel suction from the valve when the pump is running.

 

[BDY]

Hmmmm… is there a minimum pressure on a cartridge filter to make it effective? I was setting flow using the SWGC flow switch to get as low as I could… I never considered that filter pressure could also be too low to work…

I will try and raise the rpm incrementally tomorrow to see what makes the needle move off of the peg and report back.

B

 

[Rocket J Squirrel]

If you're getting air in the pump basket and the valve is sucking when you open it, your filter probably has a lot of air in it. You need to run the pump fast enough that that doesn't happen.

 

[proavia]

The quantity of water pushed into the filter when the pump is running at 900rpm is too low to keep the filter filled to the top with water when you open the air relief valve - given the height of the inlet and outlet on the filter.
Basically, at 900 rpm, the water is running out of the filter faster than it is being pumped into the filter when you open the air relief valve on the filter.

You may find that 1200rpm works much better and will also provide the benefit of (slowly) skimming the pool if your returns are correctly set.

 

[BDY]

I will incrementally raise it today to test where the breakpoint is. Will it have damaged the filter running it too low flow like I have been?

 

[Jimrahbe]

BDY,

I'm puzzled... (Not all that unusual )

Even at 900 RPM, I find it hard to believe that when you open the air relief valve that water does not come out.

Thanks,

Jim R.

 

[BDY]

So I’m experimenting this morning… at 1200 rpm and above there is enough pressure in filter to fill the tank and water comes out.

At below 1200 rpm the air gets sucked into tank. At the 900 rpm there was enough suction that if I let it go for a 15-20 seconds when i raised the rpm back to high speed it expelled air for a few seconds before waters.

@Jimrahbe Intoo am puzzled as I thought I would be able to run my VSP at any speed down to minimum (400) let alone the 700 needed for the flow switch or the 900 I was running it at 24/7.

All thoughts appreciated!

B

 

[DavidArmenB]

BDY,

I'm puzzled... (Not all that unusual )

Even at 900 RPM, I find it hard to believe that when you open the air relief valve that water does not come out.

Thanks,

Jim R.

This is something that can indeed happen depending on the individual plumbing setup and head. The top of the filter is much higher than the pump and if the return line after the filter doesn’t have way too much head, the water can indeed flow out from the filter outlet faster than the pump can fill it to the very top of the filter. This can cause the aforementioned opposite effect of air entering through the valve rather than water gushing out. I also see a similar effect in my pool and my 60sqft DE Filter: at very low (<900) rpm’s I can not use the relief valve because water will not come out of it unless I raise the rpm’s.

 

[Jimrahbe]

David's theory makes common sense, it is just something I have never seen before..

So, if the Op keeps his air relive valve closed, then I am not sure why he can't continue to run at a low RPM..

As a side note, I never recommend running less than 1000 RPM anyway.

Thanks,

Jim R.

 

[DavidArmenB]

David's theory makes common sense, it is just something I have never seen before..

So, if the Op keeps his air relive valve closed, then I am not sure why he can't continue to run at a low RPM..

As a side note, I never recommend running less than 1000 RPM anyway.

Thanks,

Jim R.

I agree, my lowest scheduled speed is 1100rpm.

And absolutely, if the air is first expelled from the filter at high rpm’s, the filter will remain completely filled with water when the rpm’s are lowered so long as there is no leakage before the filter inlet or the filter relief valve or the filter body itself.

As for the phenomenon of a little air filling in the pump basket at very low rpm’s, I also have a theory on that. The basket lid is a self sealing mechanism. The stronger the suction under the lid, the more the lid will be pushed down due to the suction from the vacuum in the basket, causing the O-ring to be squished more, which in turn forms a very strong seal. When the pump speed is reduced to below 1000rpm, the vacuum inside the pump basket is dramatically lowered. Because the vacuum in the basket is much lower now, the basket lid is no longer being pushed down the way it was before, this in turn causes the o-ring to not have the same extreme sealing effect as it did before with much higher speeds. As a result, an extremely tiny amount of air enters through the basket which slowly builds up over many hours. Of course all of this assumes the suction side plumbing is perfect and has absolutely no suction side leak.

 

[BDY]

David's theory makes common sense, it is just something I have never seen before..

So, if the Op keeps his air relive valve closed, then I am not sure why he can't continue to run at a low RPM..

As a side note, I never recommend running less than 1000 RPM anyway.

Thanks,

Jim R.

Interesting - why the 1000 rpm limit?

 

[BDY]

This is something that can indeed happen depending on the individual plumbing setup and head. The top of the filter is much higher than the pump and if the return line after the filter doesn’t have way too much head, the water can indeed flow out from the filter outlet faster than the pump can fill it to the very top of the filter. This can cause the aforementioned opposite effect of air entering through the valve rather than water gushing out. I also see a similar effect in my pool and my 60sqft DE Filter: at very low (<900) rpm’s I can not use the relief valve because water will not come out of it unless I raise the rpm’s.

That makes sense i just wasn’t expecting that…. I learn something new every day about my setup

I will bleed the tank at high rpm and then lower pump speed… thanks

 

[BDY]

Side thought - does that mean at low rpm of water can exit filter faster then the pump can fill it that it effectively causes a pulling effect of the water rather than a pushing effect? More like a siphon by the returns? (Which I have 6 of).