Hydraulic impact wrenches are powerful and can be operated for long periods of time with the right power source. These impact wrenches require a low pressure hydraulic power source and can be operated out of EWP's (elevated work platforms or aerial buckets), machinery (bobcat, tractor, excavator, etc - these items may require a flow control valve) or petrol/diesel/electric pump. Hydraulic impact wrenches can be used with long hose sets keeping the wrench away from the pump or power source. Commonly used by the power utility industry for drilling, tightening and loosening hardware on hardwood poles. Some hydraulic impact wrenches can be operated underwater.
Alternate terminology: Rattle Gun.