Got a link to the pump curve showing how much air it provides at different PSI?
How deep is the water you are pumping down under?
28" of water depth needs about 1 psi
and it takes about another psi to push the air through the stone.
So how much air is that pump supposed to give at 2 psi?
If it started out giving enough air for the stone but shortly thereafter quit, you might check to see if the diaphragm is intact or if it is damaged.
How hot is the pump getting? If the pump isn't able to push out as much air as it should, it will overheat the pump which can cause damage to the pump as well.
I'm sure you thought of this, but just in case you haven't. the active aqua pumps i use have an adjustable dial on the top. Be sure to crank it to full power.
Thanks for your reply . I torn the unit apart check all the diaphragms and then cleaned all of the castings and trash left over from manufacturing then put it back together an ran it ,had good pressure for a couple of mins the just petered out to a few bubbles , Pump is above the water line and down in the tank 30 inches Will probable just get a refund.
That's weird Paul, never experienced anything quite like that with an air pump.