pump slowly losing prime

[sjpoolowner]

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.

[PoolDoc]

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!

[sjpoolowner]

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.

[mas985]

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.

[sjpoolowner]

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/u410/kjbd123/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.

[BigDave]

sj,
You mention:
... and also open the main drain only by using that plastic thing you put under the skimmer basket ... Are you sucking air in through your skimmer? Is the water level a little low?

[sjpoolowner]

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.

[mas985]

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.

[sjpoolowner]

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.

[mas985]

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.


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.
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.

[sjpoolowner]

Thank you again. I did a little experiment and tried to block skimmer side flow using the thing and ran the pump at 3000rpm. Then to my surprise I actually noticed water flowing into the skimmer pipe. I examined the plastic thing (what is it called?) after turning off the pump and found that the flap that I initially closed the hole was actually moved. I guess it does that when the pump is running really fast and main drain only can't provide enough flow? So it looks like when I primed the pump, I actually opened both the skimmer and the main drain.

So assuming that no air is sucked into the skimmer, what are my options now? Try to run the pump at full speed regularly? Replace the o-ring? Add lube to the pump lid area?

Would appreciate any help. This issue is really bugging me now. :(

[mas985]

So I take it that even running at 3000 RPM did not remove all the air?

I removed the plastic flaps from my skimmer a long time ago. For efficiency reasons, you really don't want to restrict flow in anyway and leave everything wide open. Plus restrictions on the suction side can cause air leaks as well as other issues.

But besides the pump lid, there are several other areas where air can get sucked into the plumbing; pump drain plugs, valves, and worst case, a cracked pipe. Any construction over the buried pipes recently? One trick to find leaks in plumbing is to spray shaving cream on the various valve/plug connections and see if anything gets sucked in. If you eliminate everthing on the pad, then look again because a lot of times you may think there is no leak when in fact there is. Hopefully it isn't in underground. Air leaks can be one of the hardest things to find. Water leaks not so hard. :rolleyes:

[sjpoolowner]

Yes. What you see in the pic was as best as I could do at that moment. I might have done better if I keep repeating it. Unless I did something wrong.

What I did to prime was: stop the pump, open the air valve of the filter, run the pump at high speed (up to 3000 rpm) until water coming out of the filter air valve, close the filter valve and wait a little. I didn't open the lid since there was water in the basket except for one time to clean up the o-ring and lid surfaces. And I had to try this sequence multiple times to achieve that.

Anything to try for the lid?

I'll try the shaving cream method. I do hope it isn't in underground!

Thanks a lot.

[BigDave]

sj,
Did you happen to notice if your returns had strong flow when you were running the pump at high speed after it was primed?

[mas985]

Besides Bigdaves question above, what was the filter pressure at 3000 RPM after priming?

Also, it is somewhat counter productive to open the filter bleeder valve when the pump is off since this allows air into the filter which then displaces the water actually making it harder to prime. You are much better off opening the valve only after the pump is turned on to prevent draining of the filter.

Silicone pool lube is the best stuff to use on the pump lid and drain plugs.

[PoolDoc]

Silicone pool lube is the best stuff to use on the pump lid and drain plugs.


I am *not* disagreeing; when you need a lube on a pool pump, that's what you need. And, it can help stop leaks. (or even find them!, when goop-ed onto the inlet fitting to pipe fitting contact area)

But, gosh, I hate that stuff.

It's pretty much a last resort for me. I'll replace seals, O-rings, lids, fittings, etc. before I'll get that stuff out. It is the stickiest, hardest to get off goop I've ever dealt with, except maybe epoxy paint. But epoxy paint eventually dries, and that stuff never does. If a tube of that gets loose in a tool box . . . plan on HOURS of fun cleaning up.

And, when you put it on a pump O-ring, you can pretty much guarantee that every bit of dirt, sand, grit, leaves or twigs that get within 3" of the ring will be magnetically drawn to the goo, and then instantly and permanently attached. (Of course, that's more of an issue in the East, than on the West Coast or Southwest.)

Once there, it's almost impossible to get dirt off. Forget about a paper towel -- they aren't strong enough. You have to use a rag . . . which is then ruined for any further use. Especially, hand wiping.

Did I mention that I hate that stuff? ;) ;)

[mas985]

Ben,

I am not sure we are talking about the same thing. This is the stuff I use and for me at least, it doesn't get sticky nor does it dry up so you can easily wipe it off with a rag if you ever need to:

http://www.lesliespool.com/Home/Pumps-and-Motors/Parts-and-Accessories/68926.html

BTW, this is exactly the same stuff as plumber's silicone grease which I have used as well with the same results.

[PoolDoc]

I've used the "Jacks Magic" stuff that's been around in the pool industry for years. It's great for sticking a large O-ring -- that would otherwise jump out -- in place, say on a Challenger pump. But it's also as I said.

I have used the Rainbow chlorinator silicone, and it's not like that. The Leslie's stuff could be more like the Rainbow stuff, in which case it wouldn't be so good on a Pentair Challenger pump back O-ring . . . but it would be much better everywhere else.

[sjpoolowner]

Thank you all. My answers to your questions are:

1. The flow seems strong when I run it at high speed. As mentioned earlier, that's after 95% priming.

2. The filter pressure is 27 psi at 3000 rpm, 29 at 3100 and 31 at 3200. I think the pressure was 10-11 psi when running at 2000 rpm. I have Sta-rite system 2 PLM 200 cartridge filter (200 sq ft). Haven't cleaned it for about 2 years since I didn't notice significant increase in filter pressure yet. I plan to do it before opening the pool this year.

3. I tried to open the filter air valve after turning on the pump. Not much difference observed. I see intermittent clusters of small bubbles coming out of the returns but they seemed to stop after a while.

I decided to run the pump at 3000 rpm for hours and see if that makes any difference. I'll update this afternoon.

Based on the fact that water level in the pump basket is lowering very slowly, it looks to me that pump not being fully primed is a different issue than the air leak? Or are they actually same? Should I suspect clogged suction line as well?

Thanks again. I really appreciate your help.

[sjpoolowner]

Actually, I kept watching the returns after running the pump at 3000 rpm for 15-20 minutes and noticed the bubbles kept coming out. They are very tiny bubbles and not "shot" out of the return. Rather they just float along the wall where the return is. Very intermittent, sometimes I have to wait 10-30 seconds to see another group of bubbles. I also noticed that they come out of only one return, whose water flow is stronger than the other return's.

Does this mean the air trapped in the pump basket is slowly being pushed out and thus a good thing? Or does this merely indicate air is slowly entering into the system? I tried to look into the pump basket to see any bubbles coming from the suction but it was difficult to see inside (the lid not as transparent as I would want it to be and also air pockets made it harder).

I think I am okay even if the pump doesn't fully prime as long as it stays that way and I don't need to re-prime the pump. But I'll have to fix any air leaks.

Thanks a lot.

[mas985]

During the priming process, the pump needs to push the air out of the pump basket into the return line. If there is a suction leak, it will continuously draw air into the pump basket and out the returns. So the continuous air out of the returns is a good indication of an air leak.

You are correct though in that it the pump can operate properly with a small amount of air. But if there gets to be too much air, it can cause pumping issues. A short run at higher speed should take care of that.

[BigDave]

sj,
It seems that while you may have some air leakage, you may also have some restriction that is greatly reducing flow making it difficult to clear the air from your pump basket. I would definitley clean the filter as soon as possible, I'd also open the pump basket to look for any blockage in the impeller (after disconnecting the power of course). I'd then clean the O-ring and its mating surfaces really well and inspect for any damage (scratches etc.) before putting it back together.