The differential PSI is the pressure measured when you apply torque to the drilling motor. When you start the drilling motor and you run the needed GPM’s, the restriction in the motor will generate a PSI. This is the normal off-bottom PSI recommended for each motor. Once you touch bottom with the motor and start to drill, your pressure will rise which is known as on-bottom PSI. This is the differential pressure reading. A rule of thumb is that this is a 200 PSI increase over the regular pressure reading. If you stall the motor out, the motor will not turn when on bottom due to not enough pump or too much weight on the bit causing the differential pressure to spike. This is the time to turn off your pump, pick up off bottom and kick the pump back in and see if your pressures go back to normal operating readings. Check our Recommendations for accurate PSI readings.