Abstract: An apparatus for preventing thermally-induced stress fatigue in a vibrator support housing consists of a stress compensator that absorbs thermal dimensional changes between major structural components made of dissimilar materials. The stress compensator consists of a hydraulic clamp wedged between the free end of a vibrator actuator piston shaft and the supporting housing. Actuated by the substantially-constant system hydraulic pressure, the hydraulic clamp maintains a substantially constant clamping force between the actuator piston shaft and the supporting housing. Thermally-induced stresses are absorbed by the hydraulic system.

Abstract: A power stage servo valve for a seismic vibrator includes a stationary orifice plate defining a plurality of valve ports having a first shape. A rotary orifice plate, abutting the stationary orifice plate, defines a like plurality of valve ports that have a shape different from the valve ports in the stationary orifice plate. The configuration and shape of the rotary valve ports is such that the valve opens more quickly than it shuts off when the plate is rotating continuously in one direction at a desired angular velocity.

Abstract: A linear actuator 10 for use as a seismic vibrator includes a reaction mass 12 having an internal cylinder 14, and containing a double acting piston 20 to which are attached upper and lower pistons 26 and 28. Hydraulic fluid under pressure is applied alternately to the upper and lower faces of piston 20 to reciprocate it in alternate strokes relative to the reaction mass. Rolling diphragm seals 38 and 40, secured between piston shafts 26, 28 and reaction mass 12, prevent external contamination from reaching laminar seals 30 and 32. Shafts 26 and 28 include enlarged portions 44 and 46 that are contactable with nests of conical springs 52 and 54, mounted at the top and bottom of reaction mass 12, at the displacement limits of piston shafts. Said conical springs absorb energy and limit rebound between the reaction mass and the piston shaft.