pump slowly losing prime

Hello.
I have an in-ground pool with IntelliFlo VS-3050 pump. A few weeks back, I noticed that one of the returns was shooting water weaker than before and couldn't feel any water coming out from the other return. And when I checked the pump basket, the water level was very low. It was below the suction pipe and I could see water coming into the basket. The pump was still pumping the water, although weakly, so I guess technically it didn't completely lose the prime.

So I tried to re-prime the pump. After several attempts, I could fill the basket like 90-95% and there were air pockets on top. (Don't know why, but I had to try several times and rev up the pump up to 3000rpm to achieve that).

A few days later, I noticed that the water level went down again. I've been checking the web and asked around and I was told to clean up the o-ring (of the pump basket) and the surfaces it contacts. I did that three days ago. The water level is like 90% now but I noticed that it went down a little bit and it still looks like air is still coming in from somewhere.

Before suspecting air leaks in other areas, I'd like to rule out the pump lid/o-ring first. During the last re-prime, I didn't put any lube to the o-ring as the user manual says not to do that because the original o-ring contains a permanent internal lubricant. But would you actually recommend putting something to make sure no leaks there? I have lithium general purpose lube. Will that work? Or should I put anything special?

Thanks.

If you have a continual air leak INTO your pump, you will also have a continual air lead OUT of the pump. Unless you have some sort of continuous air vent on your filter, this will eventually show up in your pool as DISSOLVED air, that then coats everything with tiny bubbles (usually) or turns the pool milky (rarely) OR you will have a stream of bubbles showing up coming out of a pool return inlet -- it may be a small stream.

So, check that.

But in my experience it is uncommon -- it does happen -- to get an air leak so nicely balanced that it slows, but does not stop, pump flow. More often I've seen small leaks EITHER cause dissolved air but no other problems OR ELSE make the pump nearly impossible to prime, and difficult to keep running.

Another possibility is a clogged impeller. I've often seen impellers in my part of the country, clogged with pine needles (residential pools) or swim googles and toys (LARGE commercial pools) produce symptoms like you describe. On some pumps, people with small hands can feel through the back of the pump basket chamber, into the throat of the impeller, and detect clogs. But often, you have to pull the pump apart to check.


By the way, common causes of clogged impellers are
1. debris that will pass through the basket (pine needles!)
2. a cracked or split basket
3. a missing or mis-installed basket.

One episode of vacuuming with a broken or misplaced basket can be all it takes!

Thanks for the reply, PoolDoc. I forgot to mention that I see bubbles coming out of the return when the water level is low. The pump is fairly new (less than 2 yr old) and so is the basket. There are no cracks and it is correctly installed.

From my observation (I am a complete novice, though), it looks like the air keeps coming in from the suction side and the water level in the pump basket is going lower very slowly. One time I noticed the water level went down noticeably while the pump is running. The o-ring looks okay though. How can I 'seal' the pump lid area to make sure it is not the cause of air leaks? BTW, I don't see water coming out of lid when the I stop the pump.

Thanks again.

Is this happening on the pump's lower speed and how long does it take to see a bubble form after fully priming?

Also did you actually see air bubbles coming into the pump from the suction side pipe? If so, it could be a leak in any valves or pipe upstream from that.

On another note, many owners of two speed and VS pumps on lower speeds have experienced the same thing including myself. I have a few theories on this and depending how quickly the air forms, it could be either a very slow leak in the pump lid since they tend to seal better at high suction or it could be a slow outgassing of dissolved air in the water. In my own case, I believe it to be outgassing as I can see the tiny bubbles forming on the pump basket surface. When pumps run slow, they do not have enough flow rate to expell any air in the pump basket so it tends to accumulate for whatever reason. So many VS owners find they need a certain high speed run time per day in order to flush out the accumulated air.

Thank you, mas985. During the winter time I've been running the pump at 1500 rpm before I first noticed the issue and then I increased it to 2000 rpm.

In my case, I can't really seem to prime the pump fully. After several attempts to prime the pump, I was able to fill the basket like 95% (The pump lid is divided into several sections and air pockets were formed in each section except for one or two). As time goes on, the air pockets seem slowly getting larger. I attached a pic that I took right after the prime. To achieve that, I had to run the pump at 3000 rpm and also open the main drain only by using that plastic thing you put under the skimmer basket to block the flow from skimmer. Not sure if it is normal to run the pump at that high speed to prime it. Does the fact that I can't fill the basket fully indicate some problems? Or is it actually normal? I don't really remember what it was like when there was no problem.

http://i1066.photobucket.com/albums/.../IMG_05761.jpg

I didn't really notice air bubbles coming into the pump, but maybe it's because I didn't look at the pump basket too long. I'll check again.

Your theory makes sense to me, although I haven't had this issue for the past two years since it was installed (I also ran the pump at 1500 rpm for the first winter). Maybe it is because the lid doesn't seal as well as before now. So when you say 'VS owners need a high speed run time per day', at what rpm and how long? The initial setting for me was 2500 rpm when the pool vacuum or solar is on and 2000 rpm otherwise. Solar is currently off.

Is there anything else I should try?

Thanks again.

sj,
You mention:

Quote:

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... and also open the main drain only by using that plastic thing you put under the skimmer basket ...

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Are you sucking air in through your skimmer? Is the water level a little low?

No, I made sure that the water level was adequately high (more than half of the skimmer opening underwater), so I don't think air was being sucked into the skimmer.

I just checked the pump and the air pockets are much larger now than the ones shown above. The picture above was taken 4 days ago right after priming the pump.

Thanks.

Yea, that sounds like an air leak and BigDave's suggestion is a good one. The pump should fully prime at full speed or even near full speed. Have you noticed any change in the filter pressure since you have been having this problem? You can also reduce the suction on the pump by keeping both the main drain and skimmer fully open.

mas985, would you consider above picture fully primed? Or should I really not see any air pockets?

I haven't really noticed the filter pressure change. It is about time to clean up the filter (a cartridge filter) though.

I assume "reducing the suction on the pump" is bad for priming as I think I should go full force when priming? So that's why I was able to achieve better priming when only the main drain was open? BTW, I don't have any valve to control the water flow. I can only either shut off the skimmer using the plastic thing under the skimmer basket or open both main and the skimmer.

I'll add some more water just in case.

So 2000 rpm sounds too low?

Thanks again.

A full primed pump will not have any air left in the pump basket but at lower flow rates it will take more time for the air to purge. I have a 1/2 HP pump and the flow rate is around 65 GPM. It will take sometimes 5 minutes for all the air to leave the pump basket but it eventually will. However, with a VS at full speed, it shouldn't take more than a couple of minutes for all the air to be purged.

Quote:

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Originally Posted by sjpoolowner

I assume "reducing the suction on the pump" is bad for priming as I think I should go full force when priming? So that's why I was able to achieve better priming when only the main drain was open? BTW, I don't have any valve to control the water flow. I can only either shut off the skimmer using the plastic thing under the skimmer basket or open both main and the skimmer.

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What I mean by reduced suction is not reduced flow rate but reduced suction head loss as measured by "in-hg". Having the main drain and skimmer fully open reduces the suction head loss which in turn increases the flow rate so the pump should prime faster. But having higher suction head loss, will increase the suction at the pump basket (i.e. lower pressure) which in turn can draw in more air.