Pilot operated mud pulse valve and method of operating the same

Abstract From the Canadian patent

Apparatus for and a method of creating positive pressure pulses in a stream of drilling mud being circulated through a drill string is disclosed. The apparatus includes a restriction in the drill string, a valve member located below the restriction, a cylinder located in the drill string above the restriction, a valve stem connected to the valve member and extending upwardly through the restriction into the cylinder, a piston located in the cylinder and connected to the valve stem, and a restricted passage through the piston through which drilling mud can flow and equalize the pressure across the piston. In operation opening a pilot valve allows the fluid above the piston to flow through …