Please Help Me Solve A Cavitation Mystery...

[ej2010]

Hi all. Here is the situation for my 18,000 gallon pool:

When main drain valve is open 100%, the pump runs perfect.

When skimmer valve is open 100%, pump runs perfect too.

BUT, when I plug my Hayward Navigator vacuum into the skimmer, I instantly get air bubbles & swirls/cavitation in the pump chamber, and light bubbles from the pool jets (caused by the cavitation, I guess). Yet the navigator still crawls and cleans the the pool.

I have gone through a long checklist of trying to narrow down the problem:

I checked the navigator's hose for blockage. There's none.

I plugged only two hose segments into the skimmer, and still got the cavitation.

I made sure there are no pinholes in the hose.

I made sure the hose segments are tight.

I made sure there are no crimps or bends in the hose.

I took out the main filter and ran the system (still cavitation).

I switched to the spa valve and back (still get cavitation).

I made sure the Hayward unit itself had no blockage.

I removed my leaf canister from the hose (still no improvement).

So basically I only get air swirls in my pump chamber the moment I plug the navigator's hose into my skimmer. And I think this only started happening in the last week. The only thing I did differently at all in the past week was operate the spa valve on the slam system. But I don't think that has anything to do with this.

Does anybody have an idea of what may be causing this?

I'd truly appreciate any input.

Thanks,

Eric

[Mark]

In is common to mistake air bubbles in the pump basket as cavitation. Cavitation bubbles are created and quickly distroyed at the impeller so it is very unlikely that you would actually see them. However, high suction is the primary cause for bubbles in the pump basket. The air is probably being sucked in through the pump lid. Applying some pool lube on the pump lid seal will help that. Also, valves and drain plugs are another source. An easy way to find the air leak is to use a hose on various parts and see when the bubbles go away.

[ej2010]

Thanks for the reply. Why would I only see swirls of air in the pump when the pool vacuum navigator is plugged in, but never any other time? If the pump lid needed to be lubed to fix the air problem, wouldn't that same air problem occur also when the main drain is open or when the skimmer has no hose plugged into it? Why only with the vacuum unit plugged in?

[Pool Clown]

Heres an easy way to tell if it is cavitation. You need to be able to turn the pump off and see the clear lid on the pump at the same time. Watch the air swirling in the pump and turn off the pump. If the bubbles disappear instantly, it's cavitating. If they just stop swirling and collect at the top, it's likely an air leak.

[pooltech9]

I don't see anywhere in your post that you used the suction guage that comes with the Navigator to properly set the skimmer valve to operate the Navigator. It may be simply too much suction for your pump design and the already existing suction resistance in your plumbing for your pump to operate without cavitating.

[Mark]

Thanks for the reply. Why would I only see swirls of air in the pump when the pool vacuum navigator is plugged in, but never any other time? If the pump lid needed to be lubed to fix the air problem, wouldn't that same air problem occur also when the main drain is open or when the skimmer has no hose plugged into it? Why only with the vacuum unit plugged in?

The reason you see the bubbles when the navigator is connected is that the navigator adds head loss to the suction plumbing thereby increasing the suction/vacuum at the pump. Higher suction (lower negative pressure) at the pump increases the probability that you will draw in air through the pump lid or any other seal. This is a fairly common problem with suction cleaners. They require quite a bit of suction to work properly but you have a bit too much.

[ej2010]

Pooltech9: I get air bubbles in the pump chamber regardless of how open the skimmer valve is. The only way to stop the bubbles at all (and completely) is to fully shut the skimmer valve and leave the main drain open.

Mark: If I have to live with a certain amount of air in the pump chamber, say about 15% of the chamber being air swirls, is that okay for the long term health of the pump and whole system? If it's safe, I can live with it I guess.

[Mark]

Because you have the vacuum going through the skimmer, the skimmer adjustment is adjusting the vacuum of the cleaner. Set the valve to 100% main AND 100% skimmer. In other words, have the valve handle point directly between the pipes from the skimmer and main drain and towards the pipe going to the pump. This should reduce the vacuum in the pump but may still allow the cleaner to work properly. If the cleaner is not working well with that setting, slightly reduce the flow of the main drain until it does. The vacuum with the cleaner should not need to be all that high to work properly. I think you may just need to tweek the valve setting such that you have enough suction for the cleaner but not so much as to suck in air from the pump lid. However, if after adjusting the valve, there is still air in the pump basket, then try adding some pool lube to the lid gasket. This will help seal the pump lid.

[ej2010]

Mark: I did what you suggested (valve and lube), but the problem persists. I may have to throw in the towel and get a service call from the pool store that installed the pump system a few months ago.

Thanks everybody for the suggestions. If you think of anything else, please let me know.

-ERIC

[AFiremanFirst]

Most importantly! The gauge they provide is very effective, and provided for a reason. However I seldom use one either. The root of your solution is in all of the postings if you read between the lines! I suspect that when you plug in you also lose psi on your filter... stay with me. I also conclude that you have 2" plumbing because you have a very sufficient pump. with that said the navigator is closer to 1 1/4" with the ribbing. So you are losing head. You're going to laugh the solution is simple. Run the system with the skimmer open and the main drain. record your psi on your filter. because it's a navigator you may or may not be running it all by it's self (only suction to the navigator). Regardless, move your valves, to the way you would normally operate your system. 15% is probably a safe number but you will put unnecessary wear and tear on your motor with cavitation. Now, heres the solution. Gate back the pressure side of your system to re-establish your filter psi. Also, on the navigator there is a blue switch, you'll either need a flat head screw driver or a pocket knife to turn it, I wanna say it's on the right side if you are looking at the back of the navigator, you'll see I, II, III if he doesn't clean as well as you think he should play with this setting. It's probably turned to I

[ej2010]

AFiremanFirst: I'm eager to try your solution, but can you please elaborate more on this sentence: "Gate back the pressure side of your system to re-establish your filter psi". Can you put it in different words? (I'm a total layman when it comes to pool stuff).

Another thing. I get the air swirls in the pump chamber either of these ways: if the main drain is totally closed off and the skimmer is open, or if the skimmer and main drain are both equally open. So I don't know how adjust the valve will solve the problem.

Another problem is that my navigator constantly gets stuck on the main drain if the main drain valve is open even 25%.

What exactly does that blue switch do on the navigator? Does it adjust the suction?

Thanks.

[txpoolguy]

With suction cleaners, it is common to see a small amount of cavitation when cleaner is installed. Reasons are: You are adding 25-50' of distance that the pump must pull water thru (increase in head loss as mentioned before), and the cleaner hose is smaller than the 1.5" or 2" pipe that the rest of your suction piping uses. So, when you reduce the size of the hose and add 30' of length, it's easy to see why a small amount of cavitation occurs. In many cases, you must also valve back the skimmers to force enough suction for the suction cleaner to operate properly.

[txpoolguy]

The only blue switch on the Navigator is a small adjustment on the rear flap. Your owner's manual explains how to adjust it. You can download a copy of the manual at www.haywardnet.com. This adjustment increases or decreases the amount of tension on the rear flap spring. Increased tension causes the Navi to lift slightly, so it won't climb walls as much. Decreased tension causes the Navi to lower slightly, for improved wall climbing. Factory setting is "II" (options are I,II,III). Your Navi should spend 1/3 or less of total runtime on walls.

[AFiremanFirst]

"gate back the pressure side"... Your pool has a suction side, and a pressure side, suction being infront of the pump pressure being out of the pump. Sometimes, and I'm not crazing about giving this advice... you can gate back the pressure side to reduce your cavitation. But essentially you are reducing flow which could be harmful to your pump long term.

[ej2010]

UPDATE: I have a hairline crack in my skimmer pipe. Without the cleaner hose plugged in, the crack wasn't an issue. But plugging in the hose somehow exacerbated the problem and caused cavitation. My budget won't allow a skimmer replacement now, so I have some epoxy that fixed the problem (temporarily). Thanks for all the help.

-Eric

[diggler86]

Eric,

Ive got a similar problem. How did you end up determining and locating the hairline crack?

[matthew12]

The consequences of cavitation can be strong vibrations, loud noise, choked flow, erosion of valve components, destruction of the actual valve, erosion and destruction of downstream piping and finally plant or distribution system shutdown. There are numerous methods of controlling cavitation, some have stood the test of time and others are still relatively new. Its recommended that you research the solutions carefully and if selecting cavitation cages / trim approaches, give careful consideration to limitations of dual cages with pre-set elongated slots or pre-set orifices style designs and also very careful consideration on sizing based on maximum flow