Thanks for the post!

Well, the initial problem wasn't the pressure switch, but something inside the pump and typically it's the Teflon-coated piston ring...this is the most common problem with these pumps. If there is debris, a small cut or tear on the outer edge of the piston ring, you won't get full compression. If you can see light in between the outer edged of the piston ring and the cylinder, you need to replace the piston ring.

That pressure switch should certainly shut the unit off at 150 PSI. If the pump pressurizes to 150 just fine but doesn't shut off, the pressure switch is defective (assuming your tank pressure gauge is accurate). I know you just replaced it, but these pressure switches are finicky and it may need replacing again.

Also, make sure you don't have debris in the head that can get through the lines and gum up the switch and other components.

The lack of full compression could certainly have caused the initial problem, but this is not as likely as the Piston Ring causing it. The Valve would only need to be replaced if they are cracked or rusted.

Hopefully this helps, but I'm sure replacing the Piston Ring would restore full compression. The pressure switch, again, would need to be replaced if the switch doesn't shut the unit off at 150 or 155 PSI (a 5 PSI differential is okay).

- MTR