Is this pool captivation?

[bigguy6f4]

We recently bought a new house that has an inground pool. (On a side note) I am the Maintenance manager at a chrome plating facility and have general knowledge of why things happen. however my experience is more in 50hp 3 phase pumping motors and 8" piping.) We had a leak detection company come out and fix 2 leaks. (skimmer mouth and main drain)
The pump is really loud like its "captivating". The pump basket is clear. See through lid shows no air inside.

Things I have tried......
Lubed all orings and gaskets on diverters, filter cartrige housing, and pump basket.
With the SPA and POOL diverter suction side set to both.... and Spa/pool pressure side set to both the filter pressure is 5psi and the pump is insanely loud. (like rocks inside the impeller housing"
If i increase the filter pressure by diverting to spa only (pressure side) the sound goes away completely at 15psi.
Sounds to me like the motor is pumping faster than the pool/spa can supply it.
From poking around the motor control box (2 speed) I discovered some original wiring for a 2 speed pump, lots of old/new wire nuts and old/new wire strips which leads me to the conclusion that they installed a new motor. (Which only a single speed btw)
All of this leads me to 2 conclusion... Either this new pump is to large for our system, or I have some restrictions in the suction piping.

Facts worth noting.
Spa has 4 jets
Pool has 8 jets
Skimmer and main drains for pool and spa (each have 2) are 2" pvc
The piping supplying the pump motor is 2"
The diverter for the spa/pool is right in front of the pump.

Questions I would like an answer to.
What are your thoughts and questions and advice on how to fix my problem?
What is the desired psi for the filter?
What size pump should be used for a 12,000 gallon pool with spa?
The bottom of the skimmer bowl has a turtle shaped plastic device with a float and movable flapper that looks like it restricts the flow of the main drain into the skimmer. I'm guessing the float tries to prevent air from being sucked in during a low water condition. Can adjusting that flapper affect anything? ( its 85% in closed position.)

I'm sorry for the novel but I'm a firm believer that the more/better details you give the better the answer/advice you receive.

 

[JasonLion]

Welcome to TFP!

I think you must mean "Cavitation".

Cavitation is quite unlikely, but I suppose it is remotely possible.

There isn't any standard pressure for the filter, it is different on every pool.

For a 12,000 gallon pool with no spa or water features you generally want on of the smaller 1 HP pumps. However, with a spa you generally need a larger pump to power the jets correctly. In that case it is nice if you have a two speed pump, so you can run on high for the spa and low for the pool.

The float in the skimmer is unlikely to have anything to do with it.

Have you checked to see if there are rocks/pebbles in the impeller chamber? What is the HP of the pump? How do the return jets feel in pool mode?

 

[bigguy6f4]

I believe its a 2hp (I'll check when i get home from work.)

Have not checked impeller. Will try to do that soon.

Here is what gets me.....
Why would increasing the filter pressure size affect the sound. @5psi its really loud and gets quieter from 6psi to 14psi and is totally quiet at 15psi.
The added restriction at 15psi allows the suction side to supply enough water. (my theory anyways)
This is the only reason that leads me to cavitation. (thanks for the correction!)

What do you mean by pool mode? (Its a single speed pump)
The jets feel powerful with the diverters set to pool and pool/spa.