Pump Cavitating

[Thisisme]

Hi,

I have been frustrated over not being able to solve a pump cavitation issue.

I have a Jandy Stealth Original (2005 and prior) 2 hp single speed pump. Suction and return lines are 2".

There were zero change prior to the issue starting. Pool runs all year long.

So here is what I've done:

I initially changed the motor and shaft seal because, in my ignorance, I thought it was bearings.

Changed:
pump body gasket
pot lid and o-ring
union o-rings
impeller
drain plug o-rings
filter cartridges


I have also used compressed air to blow lines out, and also suction. Lines appear to be clear

Had the leak detection people out. No leaks found.

I'm sure I'm forgetting something else . . .

Any ideas would be greatly appreciated.

Thanks,
Mike

 

[mas985]

How do you know the pump is cavitating? (Note: air in the pump basket is NOT cavitation)

What is the filter pressure now vs normal?

 

[Thisisme]

How do you know the pump is cavitating? (Note: air in the pump basket is NOT cavitation)

What is the filter pressure now vs normal?

I know the pump is cavitating because of the noise it is making and there are air bubbles coming from the return lines.

Filter pressure is about 5 psi. Forgot to mention. On advice of a pool builder, I ran the system without the filter cartriges. Although the flow increased, it did not cure the cavitation. I have since replaced my filter cartriges.

 

[mas985]

Cavitation does not cause air bubbles to go out of the returns. Cavitation vapor bubbles collapse almost as soon as they are created so they do not make it out of the impeller. Air bubbles coming out of the returns is usually due to an air leak on the suction side of the pump. Pump lid, drain plugs or unions. The noise could be cavitation but it can also be bad bearings or something stuck in the impeller. It depends on the sound of the noise and some of the other symptoms.

You said the filter pressure is 5 PSI but what was the filter pressure when everything was operating normally?

Also, did all of this start to happen after you vacuumed the pool?

Can you post a picture of your pad equipment?

 

[Thisisme]

Cavitation does not cause air bubbles to go out of the returns. Cavitation bubbles collapse almost as soon as they are created so they do not make it out of the impeller. Air bubbles coming out of the returns is usually due to an air leak on the suction side of the pump. Pump lid, drain plugs or unions. The noise could be cavitation but it can also be bad bearings or something stuck in the impeller. It depends on the sound of the noise and some of the other symptoms.

You said the filter pressure is 5 PSI but what was the filter pressure when everything was operating normally?

Also, did all of this start to happen after you vacuumed the pool?

Mark,

Thanks for your responses. I am fairly certain it is cavitation by the sound. I did confirm that the old pump motor did not have bad bearings (after replacement). The sound did not change after installing the new motor.

While I do not consider myself an expert, I have read many cavitation threads, seen videos, spoke with a pool builder and pool service guy, etc. I agree that the issue is most likely a suction side air leak. This is why I have replaced what I have.

I have also disassembled the pump completely twice, and made sure there are no obstructions or damage to the impeller.

I can't tell you what the filter pressure was when it was operating properly. I believe it was higher, but honestly I don't know the number. I don't believe the pressure changed significantly when problem first started, however, it was higher than it is now.

The problem started in early spring. Nothing other than starting and stopping the pump had occurred prior the first sign of problems.

I was wondering if there is a chance the pump body could somehow be deformed at the top and not allowing the lid to seal completely, or that the diffuser cone could cause a problem. These are just a few parts that I have not changed.

Thanks,
Mike

 

[mas985]

Both air leaks and cavitation can be caused by a suction side blockage and all the symptoms point to a suction side blockage which is why I asked if you had recently vacuumed the pool.

This could also be an issue with the equipment if you happen to have a check valve on the suction side of the pump that has failed. So this is something to look into.

Or if you think it might be due to a recent debris blockage, then back flush the suction line with a hose and rag.

 

[Thisisme]

Both air leaks and cavitation can be caused by a suction side blockage and all the symptoms point to a suction side blockage which is why I asked if you had recently vacuumed the pool.

This could also be an issue with the equipment if you happen to have a check valve on the suction side of the pump that has failed. So this is something to look into.

Or if you think it might be due to a recent debris blockage, then back flush the suction line with a hose and rag.

Suction lines have been flushed using a Drain King and also using compressed air. I am confident there is no blockage in the suction lines.

There is only one valve, a Jandy 3-way, between the skimmer and floor drains. I have changed the o-rings on that valve. There is no check valve.

 

[mas985]

Can you post a picture of your equipment?

Also, has this ever happened before?

Is the flow rate out of the returns, lower than what you remember?

The pressure is lower than I would expect on that plumbing with that pump so it would appear to be a suction side restriction but I want to take a look at the setup just to see if I am missing anything.

 

[Thisisme]

Never happened prior to this. Everything worked great for over 6 years.

The flow rate is definitely down from when everything was running properly.

Here is a photo of the equipment
[attachment=1:1sipt1uc]IMG_0465.JPG[/attachment:1sipt1uc]

Here is a photo of the pool
[attachment=0:1sipt1uc]IMG_0471.JPG[/attachment:1sipt1uc]

 

[mas985]

The suction side valve, what are the two ports (skimmer and main drain?) and is there any change in filter pressure from one side to the other?

How full is the pump basket (i.e. how much air is in there)?

I am still thinking there has to be a restriction but with two suction lines, it would have be in both lines or in the pipe between the pump and valve which seems unlikely. You might just try snaking that just to make sure.

Also when you used the drain king, did you change the valve position to one port and then the other port?

 

[Thisisme]

The suction side valve, what are the two ports (skimmer and main drain?) and is there any change in filter pressure from one side to the other?

How full is the pump basket (i.e. how much air is in there)?

I am still thinking there has to be a restriction but with two suction lines, it would have be in both lines or in the pipe between the pump and valve which seems unlikely. You might just try snaking that just to make sure.

Also when you used the drain king, did you change the valve position to one port and then the other port?

Yes, there are separate skimmer and main drain lines.

I turned the solar on a while ago, and when I went out to test psi, I noticed that the pressure is just under 10 psi. The solar grid is mounted on my roof, which is 19' above the pool deck.

There is a very slight (< 1 psi) difference between the two suction lines. The pressure is slightly greater when the skimmer is selected. I'm guessing this might be due to the longer run for the main drain line.

There is very little air in the pump basket. When I took the photos, I also took video, but I don't think I can upload that to this site. Anyway there were several pea size to marble size bubbles darting around in the top 1/3.

I actually used the drain king a few times. The first time I had disassembled the 3 way valve and put the drain king in each line separately. On another occasion, I put the drain king in the line between the pump and the valve, and used the valve to direct flow to each line separately.

I used compressed air in the same way as the drain king.

I have put a snake down both suction lines, but I can't get it past the 90 degree underground. Being a rookie at this stuff, I didn't want to force it too much for fear of breaking a connection.

Thanks,
Mike

 

[mas985]

You can upload the video to youtube and then include an embedded video using the youtube button in the full editor.

The pressure should rise with solar so that is normal although 10 PSI is still very low for a 2 HP Stealth pump and solar.

You have done everything that I would have done. It is a little late now but are your sure the pressure gauge is good? Goes to zero with the pump off and if you tap it, it doesn't change pressure.

But if there isn't a lot of air in the pump basket then maybe there is something wrong with the pump. I know you replaced quite a few parts but did you inspect the diffuser for any problems?

At this point, I am just trying to think of everything. But I would like to hear the sound of the pump. Does it sound like the pump is pumping gravel?

 

[Thisisme]

I will have to post that video in the next day or so. The sound is like gravel. Similar to the video you posted.

I have a new pressure gauge. I'll update once I install it.