US Patent 8235136 Drilling and/or percussive hammer with no-load operation control

A drilling and/or percussive hammer comprises a handle and a hammer housing, which can move relative to the handle and inside of which, among other things, a pneumatic spring percussive mechanism is housed. The pneumatic spring of the pneumatic spring percussive mechanism can be ventilated via a no-load operation duct that is opened and closed by a valve. The valve can be opened and closed according to a pressing force acting upon the handle. A delay device controls the valve during closing so that the valve reaches the position corresponding to the detected pressing force only with a time delay. This causes a smooth transition from the no-load operation to the percussive operation.