Well bore communication pulser

A pressure pulse signal generator for use in drill strings in well bore operations to generate signal pulses in a stream of drilling fluid moving in the drill string bore that are detectable at the surface to detect information encoded in the pulse time related signal distribution, comprising:

• a) a housing adapted for use as a length of the drill string with means at each end for fluid tight attachment to a continuing drill string, a flow path for said stream between said ends, and having means to support a pulser body therein;
• b) a body situated in said housing and arranged to contain a battery, a down hole instrument, and means to control and actuate a signal valve to change resistance to the flow of said stream;
• c) a signal valve, arranged to move between an open state and a closed state, situated in said housing, arranged to change the resistance to flow of said stream, comprising a first spring to bias said valve toward said closed state and a power cylinder responsive to the pressure difference across said signal valve arranged to move said valve toward said open state with a force proportional to said pressure difference;
• d) first fluid channel means to conduct fluid from the downstream side of said signal valve to said cylinder to urge said signal valve toward said closed state, second fluid channel means arranged to conduct fluid from the upstream side of said signal valve to said cylinder to urge said signal valve toward said open state, and third channel means arranged to conduct fluid pressure from the upstream side of said signal valve to said cylinder to urge said signal valve toward said closed state;
• e) a servo valve situated to open and close said third channel, comprising a second spring arranged to urge said servo valve toward a second open state and a second power cylinder responsive to pressure difference across said signal valve to urge said servo valve toward a second closed state with a force proportional to said pressure difference;
• and
• f) a first flow restrictor in said first channel and a second flow restrictor in said third channel, the ratio of flow resistances of said two restrictors such that, when said servo valve is open, said piston moves toward said closed state;
• g) releasable, solenoid operated, latch means arranged to automatically secure said servo valve in each said second state when it arrives at that state, responsive to signals from said down hole instrument to release said servo valve from said secured state;
• said first spring selected to cause a preselected operating pressure differential across said signal valve to put the pulser in motion when said servo valve is opened;
• said second spring selected to overcome said second piston and urge said servo valve toward said second open state when said operating pressure exists across said orifice and to be overcome by said second piston and to permit movement of said servo toward said second closed state when signal pressure exists across said signal valve, said signal pressure being a preselected amount greater than said operating pressure.