Abstract: A fluid-powered hammer drill has a bore in which a tool shaft is normally coaxially engaged. A piston displaceable in the bore defines a front return chamber of small effective piston surface area and a rear drive chamber of larger effective surface area. A passage permanently connects the front chamber with the high-pressure side of a pressure source. A reversible control valve is connected between both sides of the source and the rear chamber for alternately pressurizing and depressurizing same and thereby alternately displacing the piston axial forward to strike the rear end of the tool shaft and axially backward. A recoil-damping sleeve surrounds the piston axially ahead of the front chamber and has a front end axially forwardly engageable with the tool shaft in a frontmost position and a rear end defining with the bore a recoil chamber separate from the front return chamber. The housing is formed with a vent passage connected to the low-pressure side of the source and opening into the recoil chamber.

Abstract: A hydraulic percussion apparatus has an elongated housing having a front nose piece and forming a chamber extending along an axis, a tool projecting axially backward through the nose piece into the housing and having in the nose piece an axially forwardly directed shoulder, and a piston axially reciprocal in the chamber and axially forwardly engageable with the tool. A high-pressure line, a low-pressure line, and a control valve can axially oppositely pressurize the piston and thereby hammer the piston against the tool. A sleeve surrounding the tool in the nose piece is displaceable axially in the nose piece between a full-forward end position axially forwardly abutting the housing and a full-rear end position axially abutting the housing and through an intermediate position between the end positions. This sleeve is formed with a radially outwardly open groove defining in the nose piece a damping compartment.

Abstract: A high-pressure source of hydraulic fluid and a sump are connected to a cyclically operating user of hydraulic fluid having a hydraulic accumulator by a high-pressure feed line having one end connected to the source and an opposite end connected to the accumulator and user. A pressure-limiting valve has an input side connected to the high-pressure line between the ends thereof and an opposite output side connected to the sump. This valve opens only when pressure in the line exceeds a preset maximum to allow flow between its sides. A detector is connected to the output side of the valve for measuring the peak pressure thereof over several operating cycles of the user and a controller is connected to the detector for operating when the peak pressure detected over several operating cycles exceeds a predetermined threshold.

Abstract: A hydraulic pressure amplifier, e.g. for generating high water pressure for rock cutting and the like, in which a differentially displaced piston drives plungers alternately to pressurize the water and is driven by a primary fluid under the exclusively of a hydraulically displaceable pilot valve. The valve member is connected by a single pilot passage to the cylinder of the piston for switching between its positions.

Abstract: A turret for mining appliances comprises a girder serving as a guide for a drilling carriage and a bolting carriage, which is mounted to pivot and slide along an axis at the end of a support arm. The girder is integral with two bearings, mounted to rotate freely and to slide on a tube provided with an anchoring point and integral with a support box articulated on the arm. The two bearings are connected by a second tube which passes through a connecting-rod which is mounted to rotate but prevented from moving longitudinally on the first tube, the pivoting of the turret being controlled by a jack pivotally connected on the one hand to the box and on the other hand to the connecting-rod. The withdrawal of the girder is controlled by another jack housed partly in the first tube.

Abstract: A feed device on a drilling and bolting turret retains anchoring bolts, before they are driven into a bore in a subterranean structure. A centering member is supported by the front part of the turret and comprises a cylindrical housing into which a circular support plate of a bolt is introduced. The shank of the bolt is introduced laterally through an aperture in the centering member. A clamping jack of the rotary and linear type, actuates a push-rod which, when it is located opposite the centering member, makes it possible to push the plate of the bolt to the bottom of the housing and retain it there.

Abstract: The body of a bit guide assembly is mounted on a base which pivots on a frame about a first pivot point and may thus be retracted in order to allow the passage of the anchoring bolt screwed after drilling a hole. A double-acting jack has its rod pivoted on the base, whereas its body is pivoted on a dog, in turn mounted to pivot on the frame about a second pivot opposite the pivot point. The dog comprises a locking tooth which cooperates with the end of the base remote from the first pivot point. The free end of the dog cooperates with a retaining tooth formed on a connecting-rod, mounted to pivot about a fixed pin and biased by a spring against a stop. The same jack thus controls the retraction of the bit guide, for bolting and its locking in the lowered position, for drilling.