The control valve circuit used to date on many poppet orifice pulsers utilized in the Measurement While Drilling industry consists of a small poppet and orifice arrangement. This allowed a low power supply draw and a simple system design. There were several negatives to this arrangement. The first was the small dimensions inherent with this design criterion. It is subject to plugging which then negates the pressure communication and the functioning of the main valve which generates the pressure pulse. The second issue is the limitation to how rapidly the solenoid can be fired with the limits put on the system by its power supply, typically batteries. The valving mechanism can only be fired as rapidly as the capacitors can be charged delivering the power to the solenoid.
A stepper motor powered rotary valve solves both of these issues. It allows a much larger flow path through its elements allowing improved tolerance to debris in the drilling fluid. As well its speed is much greater than the solenoid powered poppet orifice control valve. The benefits go further. The stepper motor powered rotary valve has much more flexibility than the “on- pause –off – pause” pattern limit of a linear poppet orifice valve. The stepper motor allows precise positioning, direction change, as well as rotational speed variations to alter the movement and resulting reaction of the main poppet orifice pulse generation valve. In effect many of the pulse patterns generated by a rotary main valve pulser can be emulated with the linear poppet orifice style valve as well as some that can not. In addition the issue of plugging with the rotary main valve pulser is eliminated since the signaling valve is a poppet orifice not a rotary valve which when closed to generate its positive pulse signal creates very small restrictions around the rotor stator elements. It is during this phase that a rotary pulser design is very susceptible to plugging and jamming as the entire flow of the mud through the drill string (and the rotary signaling valve) must pass this restricted area. The mechanical forces act to lock the valve and increase as the flow area in the closed position becomes restricted with debris and the pressure increases. On the other hand a poppet orifice linear pulser in the same pressure pulse generation stage does not have the same locking forces applied due to its geometry. In some arrangements it the forces would actually force the valve open.
Finally due to the fact that the stepper motor rotates a valve the design is simplified from other designs which operate a small poppet orifice converting the rotary motion into linear movement to actuate the poppet orifice control valve. All of this combines to make this method of design a unique improvement on present applications.
