Is my pump cavitating?

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C

cj133

Well-known member
May 6, 2018
719
NJ
Hi all,
I finally got my filter and everything running and I'm not sure if the pump is cavitating due to my setup, or if I still have a leak somewhere, or, if it's just pulling air from the skimmer.
I'm using a Hayward 1.5HP 2 speed Matrix pump.

Here's a video I took yesterday. :

The pump in high speed definitely sounds like there's air in it but I don't see much going in, though there are some very small bubbles but barely.
In low speed it sounds beautiful.

Is a single skimmer with a 1.5" hose not enough for a 1.5HP pump? Is it likely cavitating or do I just have an air leak somewhere?
My plans were to use high speed for vacuuming, but if it's cavitating without a 30' hose on it I'd imagine it's going to be much worse with a vacuum.

If I restrict the return more it quiets right down and I'm running a 3/4" eyeball.
 
Is the water level 1/2 up the skimmer throat?

Clean and lube the pump basket lid o-ring using silicone based pool lube. Be sure to clean the mating surfaces too.

Does it sound like rocks/pebbles rolling around in the pump? If so, that's usually cavitation - just throttle the return down a little. It's possibly a little too much pump for your plumbing.

If there was an air leak, you would probavly see a bit of air thru the pump basket lid when running on high speed (you may see a smallish air bubble running on low, but that is relatively normal).

You can run on low most all the time - the filter will actually work better with the lower flow. Only use high when vacuuming, running your automated cleaner, or for quickly skimming the surface.
 
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Water level looks low. The skimmer weir should be at ~45 degrees, yours look flat. Confirm the water is 1/2 way up the skimmer inlet. Yes, your pump is cavitating, possibly because of this but you may have air infiltration on the suction lines or the pump basket lid.
"If I restrict the return more it quiets right down and I'm running a 3/4" eyeball. "
Cavitation does not require an air leak, it may just require that the water supply is inadequate for your pump's capacity. The "vacuum" created lowers the evaporation point of the water such that it vaporizes ("boils") - classic cavitation.
 
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sktn77a said:
Water level looks low. The skimmer weir should be at ~45 degrees, yours look flat. Confirm the water is 1/2 way up the skimmer inlet.

Yes, your pump is cavitating, possibly because of this but you may have air infiltration on the suction lines or the pump basket lid.
Click to expand...


Skimmer is more than half full.
104459
 
Based on your last pic, the water level looks fine. My bet is the pump trying to pull in more water than the plumbing can provide - leading to cavitation. Throttling the return line will help.

And as Keith indicated, there could still be air leaks in the intake plumbing. You can run water from a garden hose over/around all the suction side connection and the pump basket lid. If you can hear a sound change, you may have a leak at the spot where the sound changed. Most likely suspects are the pump basket lid, skimmer to hose connection and hose to pump connection.
 
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To me it sounds like a ton of air is passing through the pump it self and yet the strainer housing is pretty much air free as is the clear hose to the filter so I assumed it's boiling in the pump.

Does anyone think piping it in PVC would be enough of a change to fix the issue or is a single skimmer like this just never going to be enough?

My other thought was to add a 3 way ball valve at the inlet of the pump and use it to split between the vacuum and skimmer.
 
A wider overall view of your equipmemt area may help us give you some options.

Do you have a suction side cleaner? Setting up a dedicated suction port for it and dividing the suction between it and the skimmer might help. And if you're not using the cleaner, run on low to save electricity.
 
proavia said:
A wider overall view of your equipmemt area may help us give you some options.

Do you have a suction side cleaner? Setting up a dedicated suction port for it and dividing the suction between it and the skimmer might help. And if you're not using the cleaner, run on low to save electricity.
Click to expand...


Here you go. Please excuse the mess as I'm still cleaning up the yard.

Manual vacuum only.

The only thing in between the filter and pump is a hose.

104540
 
Water flow looks good in the skimmer box, no vortex. Discharge pressure looks stable at 15 psi on high and I can't hear anything except a normal 1.5 hp pump running at 3450 rpm. As previously mentioned cavitation sounds like there's marbles in the pump. Don't really hear that but if you suspect a leak in the suction trickle a water hose at the joint or fitting. If the pump sounds different that's your leak. If not it's just a pump running normally. At high speed they are noisy.

Chris
 
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Since you have a manual vacuum, you don't want to leave a manual vacuum head unattended in the pool - especially while anyone is using the pool. Just use high when vacuuming and low at other times.

All pumps are much louder when running at high speed.
 
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I'll try to get a better audio recording tonight or tomorrow.

But everything else aside, would it be expected for a 1.5HP pump to cavitate under these conditions? What about pulling from only a manual vacuum with 35' 1.5" hose?
 
I've got a 1hp 2 speed pump on my 15k gallon in ground with 2" piping. So motor may be oversized.
 
sktn77a said:
Not normal - it's cavitating. Try 1/2" eyeballs or run it at 1/2 speed. Have you tried vacuuming with it yet?
Click to expand...
\
No not yet.
If it's cavitating without an extra 35' of hose I see no reason to try it though.

I'll just add a 3 way valve at the pump and make it so I can connect the vacuum right there and then split between the skimmer and vacuum to use high speed while vacuuming.

Low speed is more than enough for my small 15x24 pool anyway. The only reason I ended up with this pump was it was a package deal and in my opinion, overall the best. They only offered single speed pumps from 1HP to 2 HP and this was the only 2 speed pump. I knew 1 HP was too much so I went with the 1.5 2 speed. That, and I wanted the bigger filter that came with this pump anyway.

In low speed I've basically got a 250LB sand filter and a 0.15HP pump. It's a beautiful thing.
 
sktn77a said:
Just curious if the cavitation got worse (I would imagine so). 3 way valve sounds like a good compromise.
Click to expand...

Ah.
I tried closing the ball valve I have on the skimmer and it made it progressively worse.

I ordered a Hayward 4 way ball valve, which apparently is a variable 3 port valve. Hopefully my 35' vacuum hose will end up long enough.

Is anything easy? :)
 
So, I swapped the 3/4 eye with a 1/2" one and the pump certainly is quieter and the cavitation sound completely goes away.

However my pressure goes up from 15 to 19 psi and the return hose stretched out more. In low speed I go from under 2 psi to 3 psi


I tried feeding it both my manual vacuum and skimmer and it still sounded like it was cavitating and the vacuum was weak. With the vacuum alone it was good and strong but sounded unhappy. That was with the 3/4 eye.

I don't know.....
 

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