Servo valve having a retro action on the pressure

摘要

An apparatus for reducing the harmonic distortion and giving a more linear response in a hydraulic vibrator, which apparatus generates a seismic signal in the surface of the ground and includes a servo valve (18) of the flow rate-control type comprising a bypass pipe (46, 47) and pipes (35, 35A, 39, 39A) for hydraulic retro action between the outlet orifices (29A, 29B) and the inlets (16, 17) of the servo valve in order to create a negative differential pressure retro action exerted on the main stage of the servo valve. The force developed in the actuator of a hydraulic vibrator (32) is a direct function of the pressure applied to the hydraulic piston. The changes in pressure head (load) due to the conditons of the surface of the ground being reflected in the form of changes in the pressure exerted on either side of the hydraulic piston. The pressure can better be controlled in an actuator if it varies merely as a function of the input signal, and the natural response of the vibrator becomes more linear and the harmonic distortion may be reduced by using a servo valve of the type having pressure control.