alternatively a hollow shaft one end of the motor shaft is attached to shaft 106 and the other end of the motor shaft is attached to torsion spring 105 the other end of torsion spring 105 is anchored to end cap 115 the torsion spring 105 along with the shaft 106 and the rotor 103 comprise a mechanical spring mass system the torsion spring 105 is designed such that this spring mass system is at its natural frequency at or near the desired oscillating pulse frequency of the pulser the methodology for designing a resonant torsion spring mass system is well known in the mechanical arts and is not described here the advantage of a resonant system is that once the system is at resonance the motor only has to provide power to overcome external forces and system dampening while the rotational inertia forces are balanced out by the resonating system fig3 a shows a typical torque signature acting on an oscillating shear valve the torque acting on the rotating disc is subdivided into three main parts the torque due to the fluid force 310 the dynamic torque caused by the inertia and acceleration 315 and the counterbalancing spring torque 320 example is taken for.