Pump cavitation?

[JulieMor]

After five years of dormancy we finally got the hot tub going again.  Long story.

Before, one pump was a bit noisy.  In the rebuild, we replaced all the seals on the pumps (Wavemaster 7000).  I had hoped that would take care of any problems.  I wasn't able to remove the rotor from the housing.  Something was locking it in.  So I did my best to examine it and add lubrication wherever I could.  I couldn't access the bearings.

In taking apart the first pump (the noisy one) I split the impeller at a glue joint.  I epoxied that back together doing my best not to leave behind any squeeze out.

When everything was back in the tub and it was filled, I ran the pumps but the noise problem wasn't cured.  We were in it last night and it seems the noisy pump isn't putting out the same pressure as the other pump.  They both feed about the same amount of jets.

Listening to it, it sounds like there's air inside.  That pump still has a small leak at the bottom of the suction cover.  I tightened the V-clamp but it didn't help.  Maybe the O-ring (new) didn't seat properly.  I'll be taking that out and fixing it (hopefully) next week.  It had a leak there before too.  Could that be enough to let air in and cause reduced pressure?  Or could it be a worn bearing?

BTW: When the air inlets are shut off, I can't see any noticeable air bubbles coming from the jets. 

[TwinCitiesHotSpring]

sounds like bad bearings to me...unfortunately replacing a pump seal and/or gaskets will not help the situation, your going to need a new motor or have a electric motor shop replace your bearings...as far as the drip is concered your o-ring could have a slight pinch or twist in which case I would open it back up, lube the gasket, maybe turn it over and attempt to re-seal (tapping the clamp with a small hammer as you are tighenting it may help to seal as well) good luck

[Chas]

Tapping is a must! You have to spread the tightening force around the entire circumference. But you didn't mention a water leak, so I'm betting you have that ok. If the pump is sucking air it will leak water when you shut it down.

These pumps are 'close coupled,' which means that if the seal leaks the water goes right into the motor. It can mess things up good in there, or it can simply ruin the bearing on that end of the motor. I am one of the only dealers I know who actually will pull the end off a motor and put a new bearing in, but the motor has to be more than a lump of corroded parts or I can't get it apart for the repair.

[clover]

Your solution is a NEW pump.  When a pump seal leak is allowed to continue, it only makes things worse.  Chas is right, without attention, you can see the chemical affect on the parts and when corrosion is obvious, you are wasting your time and money to attempt any repairs that will be long lasting.

As the pump seal leaks, centrifugal force causes the chemically treated water to travel back into the motor washing the lubricants out of the bearings.  With a new seal installed, you deny water to the bearings that now run dry making noise and eventually seizing up usually within six months.

Imagine paying me to replace the pump seal and have that occur.  This now enters the area where the customer says, "every since you fixed it I have had this problem."

Secondly, when you damage the impeller, replace it.  When you try to repair it, keep in mind it makes 3400 revolutions per minute, or 56 per second.  Proper balance of the impeller is a critical concern with centrifugal force.

Best advice, cut your losses now, and replace the pump.

[JulieMor]

I removed both pumps and took them apart.  This time I was able to remove the rotor and get to the bearings.  The "quiet" pump (also the one that pumped water just fine) was the one with the epoxied impeller. 

As I opened up the wet end and examined the O-rings, I noticed a bit of grease on them.  Then I remembered when I took them apart the first time there was grease on the O-rings and in the grooves of the suction cover, probably to help seal it better.  I cleaned it all off from the pump housing before I installed new O-rings and didn't replace it.  This time I greased up both O-rings with a waterproof silicone grease before reassembly.

When I got the rotor out (it took a few good whacks with a rubber mallet) I examined the bearings.  They are sealed bearings but the only thing I noticed was some of the grease had oozed out of the plastic seal.  The bearings were tight, no play in them at all.  Checking it against the bearings of the "quiet" motor, I saw no difference.  The bearings fit on the rotor shaft tightly and the rotors spin freely.  There was no indication of any play at all on either motor.

The pumps are back in now but I can't fill up the tub yet (pump leaks weren't our only problem) so I don't know how this will work,  I'll post here when we getting it going again.

Thank you all for your replies.  You gave me a lot of food for thought and compelled me to figure out a way to get to the bearings.