Is air in pump basket while running normal?

[mas985]

Think of the pump and motor as two separate machines. An induction motor will always run synchronous to line frequency with slip or around 3450 RPM with a load. Changing the impeller to a smaller one doesn't change this much but it will reduce the load on the motor so the slip may reduce slightly but I wouldn't expect the speed to change by more than a few RPM.

As for the resulting head curve, the wet end alone, including the impeller determines the head curve. So if you decide to go with the impeller of the 3/4 HP pump, that is the head curve that will result. It doesn't matter that you have a higher HP motor on a lower HP impeller. The impeller will dictate the performance of the pump. The motor will just use less power.

 

[whoozer]

I am now having a similar issue, the difference is mine never did this before and now it is coming and going. I have a new pump and filter coming in about a month but I have a bad feeling something is clogged somewhere as my pool has been sitting for 3 years. Can you explain this drain king thing and how it helps find a possible plug?

 

[mas985]

A Drain King doesn't really help find a clog, it only helps to clear one. It fits on the end of the hose and is placed in the pipe leading to the pump on the pump side. When it is turned on is swells to close off the pipe and it forces pulsating water into the pipe to help break up a clog. However, I have found that a hose and a wet rag are just as effective. Is is really the water pressure which clears the clog. The pulsating effect might be useful for stubborn clogs but for most a hose should work fine.

 

[kabbak]

Think of the pump and motor as two separate machines. An induction motor will always run synchronous to line frequency with slip or around 3450 RPM with a load. Changing the impeller to a smaller one doesn't change this much but it will reduce the load on the motor so the slip may reduce slightly but I wouldn't expect the speed to change by more than a few RPM.

As for the resulting head curve, the wet end alone, including the impeller determines the head curve. So if you decide to go with the impeller of the 3/4 HP pump, that is the head curve that will result. It doesn't matter that you have a higher HP motor on a lower HP impeller. The impeller will dictate the performance of the pump. The motor will just use less power.

OK, thanks. Great explanation. I think I understand.
With a smaller impeller, the motor slips less as less power is needed due to the reduced torque required. With too "big" an impeller, a lower horsepower pump can't slip enough to get enough torque * rpm to keep the impeller fed. It might even overheat. No?
Thanks!

 

[mas985]

Correct, the size of the impeller dictates how much power the motor needs to deliver and how much it will draw. So if the motor is not rated high enough for the power that is needed, it will likely fail fairly quickly.

 

[kabbak]

So a year later basket is still not completely filling and pump is still noisy.
I realized I actually have a pre 1990, Hayward super II pump -- not the lower capacity max-flo. So looks like it's WAY too much pump for my 1.5" suction and return lines.

Power draw is 6.1Amps with 248V.
Plugging one of the two return eyeballs results in the basket filling and pump quieting and filter pressure rising from 13 - 19psi.

I filled 5 gal buckets (via short 3/4" ID vinyl hose) to find total actual flow is ~36GPM. This implies a huge (full atmosphere) suction head so impeller is likely pumping air though not seen in pool (as it redissolves?)

Questions:
1. Will "standard" 1/4" npt threaded vacuum gage fit into one of the pump drains to get suction vacuum to verify?
2. Does it seem like the absurdly expensive intelliflo pump set for like 25 GPM is the right answer here since replumbing everything is even more expensive?

Thanks!

 

[mas985]

Sorry to hear that you are still having this issue. As to the answer to your questions:

1. Yes it should work.

2. If you are not sure what is wrong, then putting an Intelliflo on bad plumbing could be a problem as well.

Did you ever separate the motor from the wet end and actually inspect the impeller?

The vacuum measurement would help. A low value would indicate that something is wrong with the impeller. A real high value would indicated a suction side blockage.

 

[kabbak]

Sorry to hear that you are still having this issue. As to the answer to your questions:

2. If you are not sure what is wrong, then putting an Intelliflo on bad plumbing could be a problem as well.

Yes, I agree and am trying to rule out things that the Intellipro wouldn't solve.

Did you ever separate the motor from the wet end and actually inspect the impeller?

No. Was thinking I would replace with smaller impeller when I did so, though now seems pointless as so little change would result. For my edification, how might an impeller problem result in my under filling?
Also, doesn't it seem this pump is too much for 1.5" lines and for allowing long run times to lower cost and reap related benefits?

The vacuum measurement would help. A low value would indicate that something is wrong with the impeller. A real high value would indicated a suction side blockage.

I have the gage. Just need to stick it on. Will do very soon.
BTW, what's your recollection on the highest vacuum you've ever seen on the suction side when it was still able to deliver around 36 gpm.
Thanks very much for your help!

 

[mas985]

Also, doesn't it seem this pump is too much for 1.5" lines and for allowing long run times to lower cost and reap related benefits?

If the impeller were damaged, it might not produce enough flow rate to push the air out of the pump basket. But suction side blockage also has the same symptoms although the suction at the pump would be significantly different.

BTW, what's your recollection on the highest vacuum you've ever seen on the suction side when it was still able to deliver around 36 gpm.

Well it has to be less thabn 30" of Hg or water vaporizes (cavitates) but you need a couple of inches to account for the drop inside the pump as well so somewhere around 28" measured at the pump drain plug would be where cavitation starts. The maximum I remember hearing about is probably around 22".

However, even those values do not drop the flow rate to 36 GPM which makes me think you have a broken impeller. Based upon your description of your plumbing, I estimate that a fully functional 1 HP full rated Super II should produce about 65 GPM @ 63' of head and the suction would be about 9" hg. If I add suction head loss enough to bring the suction to 25", you would still get 56 GPM @ 68' of head. So I don't think it is possible to have 36 GPM without something being wrong with the impeller and/or wet end. You can get to 36 GPM with return side head loss but not suction side. You could also have high head loss between the pump and filter gauge.

 

[kabbak]

Should I expect to be able to disassemble the pump for wet end inspection w/o needing to replace anything (seals, gaskets,etc.)?
Or should I first get those items as they'll likely be destroyed/not reusable?
Looks like we're finally getting to the bottom of this!
Thanks much Mark!

 

[mas985]

You shouldn't need any seals unless you remove the impeller from the motor shaft. Normally, the gaskets/o-rings can just be re-lubed with some silicone pool lube unless they are damaged when removed.

However, as I mentioned before, the issue could also be between the pump and filter. Measuring the pressure at the pump drain plug instead of the filter could reveal if that is an issue.

 

[kabbak]

This just in...
Running vacuum at pump drain plug under the inlet port is 23 inHg on new, liquid filled, vacuum gage that reads zero with pump off.
My decoder ring says that's a 11.3 psi drop and adding the 13.5 psi at filter, the pump is creating 24.8 psi of differential head or 57.3 ft.
My (SP3010EE) super II pump curve indicates ~75 gpm at that head, but my bucket filling found only ~36.

Vacuum decreases to 10.6 psi and filter pressure increases to 17.5 psi when nearest to pump eyeball is plugged. Pump also gets quiet though basket still has lots of air at the top of basket.

11.3psi suction drop seems huge with ~ 36' of distance between skimmer and pump. Even if needed 6 elbows.

So as mas985 suggests, either my impeller is kafluey and/or there is serious suction weirdness here. I don't have lots of air at eyeballs so maybe impeller is running in partial air (lowering pumping effectiveness) that redissolves at filter? I'm obviously guessing here.

FWIW, the pump outlet port plumbing is a short 2" straight to 2" elbow to 1' straight into filter's inlet union. Post filter plumbing is 1.5".

Next I'll pull pump apart and check wet end guts.

Any thoughts?

 

[mas985]

23 in hg is extremely high suction and would most likely cause the pump to draw in air from almost anywhere. I don't think that can be normal and would suggest a suction side blockage of some sort. So the impeller is fine. Is there only one suction line for the main drain and skimmer?

 

[kabbak]

23 in hg is extremely high suction and would most likely cause the pump to draw in air from almost anywhere. I don't think that can be normal and would suggest a suction side blockage of some sort. So the impeller is fine. Is there only one suction line for the main drain and skimmer?

There is only one line. Main drain comes up into skimmer under a low water level "valve" and then skimmer is plumbed back to pump shed. FWIW, main drain line appears to be copper up to skimmer.

I'll try a Drain King again to flush basket back to skimmer and leave it on there a while. I was also thinking of trying to pull a 1" jawbreaker candy (dissolves if stuck) threaded on heavy monofilament line from the pump back to the skimmer with the pump off. If that's possible, the blockage isn't full diameter.

Prior attempts to fish snake-like things into suction side have failed due to sharp bends near both ends. Any suggestions there?

Re the impeller, do you buy the notion that the low flow I measured may be due to air at the impeller?

Thanks so much Mark.

 

[mas985]

Re the impeller, do you buy the notion that the low flow I measured may be due to air at the impeller?

Yes, having a lot of air will reduce the flow rate.

As for the potential blockage, the drain king is probably your best bet but if you have a small copper line from the pool to the pump as well, that could explain the high suction and a drain king won't do anything. If that is the case, the smaller eyeball orifice would help.

 

[kabbak]

Another round with drain kings of various sizes and a rag wrapped hose failed to dislodge anything from the suction line. I flushed from the pump basket back to the skimmer with basket and float valve removed for over 40 minutes total.

I also used a 30" (all I had) 3/16" dia. snake to probe pump and skimmer ends of the line. Again nothing found.
Pump behavior and pressures are as they were before I started.

I confirmed a single 1.5" pvc fitting in skimmer back to pump and what looks like 1" copper from main drain into skimmer. Both under skimmer's float valve. I also verified that running without the float valve (just the strainer basket) makes no difference.

So other than the pass a jawbreaker through the length of the pipe, I'm at an impasse regarding detecting/clearing a blockage.

How likely is it that a blockage would be far from either end of the suction line?
I would expect it to be near the various fittings rather than in a straight section.

 

[duraleigh]

kabbak and mas985,

I'm jumping in without reading the entire thread.......have you eliminated a suction side air leak? If so, I'm sorry.....I couldn't find that being vetted in the thread.

 

[gullzway]

See my sig for setup.
The basket isn't completely filled. I can see the horizontal "column" of water entering the basket from the inlet pipe (supply is 1.5", exit is 2"). I'm not talking bubbles like from cavitation, it's just not filled and is stable like this while running.
Skimmer looks well filled, if anything pool level is too high (recent rains). It seems unlikely air's entering from there and the air condition is not intermittent.
I checked that the basket cover is well seated on clean o-ring.
I estimate pump is 22' from pool. Pool has single bottom drain and single skimmer on end of pool nearest pump.
Pump seems pretty noisy too.

Is the pump too big for the inlet plumbing? I've been considering reducing to 3/4 HP SF 1.27 or even SF 1.
Any thoughts on what's going on or what to check.
Thanks so much for your help!

My old super II was doing the same thing all last year. I noticed a hairline crack in the center of the lid this year. I replaced the Pump Lid for $39 and the air is completely gone. You might inspect your basket Lid closely.

 

[mas985]

What concerns me the most is the 23" hg on the suction side. That is very high and air will leak into the system with even the best seals or the smallest of gaps that wouldn't normally leak. Given the copper pipe for the main drain, my suspicion is that there is a smaller pipe between the skimmer and pad. If so, then the only thing you can do to reduce the suction and thus eliminate the air leak is to increase the return pressure and the best way to do that is by reducing the eyeball diameter.

 

[kabbak]

Re suction leaks, I've checked and poured water around, lubed o-rings etc.

I'll recheck the cover for cracks. Was cover screw on or clamp down type? I have the latter.

... Given the copper pipe for the main drain, my suspicion is that there is a smaller pipe between the skimmer and pad. ...

Had a trench open for a while with the plumbing from pool shed to pool. There were at least four lines. Two 1.5" PVC and two 1" PVC. However, I could not see under pool concrete, but looking into the skimmer, return to pool is 1.5"

Yes, the 23inHG suction seems ridiculous for a 36' distance, even with a lot of elbows!

Thanks all for the suggestions and help!