A downhole drilling system comprising a drill bit and a controllable pulsing drilling device comprising a fast acting valve having: a guide pole having a guide pole channel; an actuator mounted for axial movement on said guide pole; a pilot seat; an actuator seat; an actuator orifice; a connecting channel; an internal chamber; a pilot valve being configured for stopping fluid flowing through the guide pole channel and for backing up flowing through the connecting channel to the internal chamber; for filling the internal chamber with fluid and moving the actuator on said guide pole toward the actuator seat when the pilot valve is in contact with the pilot seat; restoring flow through the guide pole channel thereby draining the internal chamber and the connecting channel such that the actuator withdraws from the actuator seat when the pilot valve does not contact the pilot seat; restricting flow of said fluid through said actuator orifice resulting in a sudden increase in pressure of said fluid on one surface of said fast acting valve wherein said increase in pressure results in a first unidirectional axial force creating a pulse through said pulsing drilling device; said restoring flow through said actuator orifice for creating a second unidirectional axial force creating a pulse in the opposite direction as said first unidirectional force when said increase in pressure is released; characterized in that the downhole drilling system further comprises a bottom hole assembly comprising said drill bit; said restoring flow through said actuator orifice further comprising forcing said fluid through said drill bit and allowing for cleansing said drill bit from particles formed during drilling a formation; said pulsing drilling device being applied directly above said bottom hole assembly. a guide pole having a guide pole channel; an actuator mounted for axial movement on said guide pole; a pilot seat; an actuator seat; an actuator orifice; a connecting channel; an internal chamber; a pilot valve being configured for stopping fluid flowing through the guide pole channel and for backing up flowing through the connecting channel to the internal chamber; for filling the internal chamber with fluid and moving the actuator on said guide pole toward the actuator seat when the pilot valve is in contact with the pilot seat; restoring flow through the guide pole channel thereby draining the internal chamber and the connecting channel such that the actuator withdraws from the actuator seat when the pilot valve does not contact the pilot seat; restricting flow of said fluid through said actuator orifice resulting in a sudden increase in pressure of said fluid on one surface of said fast acting valve wherein said increase in pressure results in a first unidirectional axial force creating a pulse through said pulsing drilling device; said restoring flow through said actuator orifice for creating a second unidirectional axial force creating a pulse in the opposite direction as said first unidirectional force when said increase in pressure is released; characterized in that the downhole drilling system further comprises a bottom hole assembly comprising said drill bit; said restoring flow through said actuator orifice further comprising forcing said fluid through said drill bit and allowing for cleansing said drill bit from particles formed during drilling a formation; said pulsing drilling device being applied directly above said bottom hole assembly.