The present invention relates to an accumulator for a liquid driven hammer device.

In liquid driven hammer devices one uses accumulators to smooth pressure variations in the hydraulic system and see to it that the hammer device momentarily is provided with a sufficient amount of hydraulic liquid during its working stroke. In previously known accumulators, see for instance US 4264107, gas volumes under pressure are used to take care of the momentary flows caused by the pressure pulsations. The liquid can hereby be separated from the gas volume either by a membrane or by a piston. Both these alternatives are shown in US 4264107. Both these accumulators have the drawback that they have to be supplied with pressure gas, usually nitrogen, at intervals since there is a certain leakage. It has turned out that the gas leakage through a rubber membrane at lower pressures becomes larger through the pores in the rubber membrane than at higher pressures which results therein that a low pressure accumulator loses its accumulator capacity after a relatively short time. If, furthermore, the pressure is relatively high there is the additional drawback that the accumulator must be made and tested according to actual pressure vessel norms.

This is both time-consuming and requires special equipment.

According to another impact device, see EP 885693, it is previously known to replace the accumulator gas with a body of foamed plastics to bias the membrane. The membrane is kept because the foamed plastics is exerted to destructive influence when in contact with hydraulic fluid, EP 885693, col. 1, lines 47-50.

The present invention, which is defined in the subsequent claims, aims at avoiding the above mentioned drawbacks. This is achieved by replacing the normal gas accumulator with a body of foamed plastic, preferably microcellular polyurethane, provided with a sealing surface layer, preferably in form of a lining of polyurethane, to separate the liquid with varying pressure from the inside of the body. In this way it is possible to dispense with the accumulator membrane. The invention thus makes it possible to place the accumulator closer to the place where pressure variations are created.

An embodiment of the invention is described below with reference to the acompanying drawing which shows a section through an accumulator according to the invention.

The accumulator shown in the drawing is intended to be mounted in a hydraulic conduit where one has a varying pressure. The idea according to the invention is however not limited to conduit accumulators but can equally well be directly connected to a machine which has channels with varying pressure to smooth large pressure variations and reduce the risk for cavitation. It is also possible to place the accumulator inside the machine close to the source of pressure vaiations. The accumulator shown in the drawing comprises a housing 1. Housing 1 comprises a central part 6 and a cylindrical part 7 about it. Between parts 6,7 there is a room 2 in which a body 4 of foamed plastics is arranged. Body 4 is provided with a surface layer 5. The central part 6 surrounds a channel 3 in which a liquid with varying pressure is situated. The central part 6 comprises a number of radial openings 8 which connect channel 3 with room 2. Cylinder part 7 is kept in place by an end piece 9 and a nut 11. In use hydraulic conduits are pressed against conical surfaces 12 and 13. The foamed plastics body is advantageously made of microcellular polyurethane, and the surface layer 5 which separates the inside of body 4 from the liquid with varying pressure is advantageously made of a sealing lining of polyurethane.