impeller cavitating

[matt4x4]

What happens inside the pump? Does it start to get a big airspace under the lid?
Does it stay filled with water but nothing comes out of the return?
It sounds pretty normal, but if you get a big air space under the lid while blocking the skimmer, then you have a suction side leak, it could be the lid gasket or anywhere along the line from skimmer to pump intake.

[fuelman]

No, it does'nt form air under the lid.
It just seems to me that if you say put your finger in the return jet that the pressure gage should rise higher then 10PSI. and not drop off. I would think that once the sand starts to trap enough debris to raise the gage to around 10PSI that the filter would just stop working.