The Owner's Manual is available as a PDF download under our Specs tab. On page 7 of the manual it says once the unit is turned on the motor starts when the spray gun trigger is pulled, shuts off when the spray gun trigger is released.
However, on Page 9 it also says to turn the unit completely off if you step away for more than 5 minutes. This protects your pump from overheating, since the unit depends on water rushing through it to keep it cool.