RELEASE PRESSURE - Next you will have to relieve any pressure that remains in the pool pump and water lines. To relieve pressure turn the air relief valve on top of the pool filter counter clockwise. You will hear air releasing as you see the pressure on the pressure gauge go to 0 psi. Leave this relief valve open.
TAP INTO STEM - With a rubber mallet or hammer, lightly tap the head of the small screw driver into the broken lock knob stem. Be careful not to get into and damage the threads. This will create a slot that you will use to remove the broken stem (similar to the top of a slotted flat head screw.