Patent GB-1492698-A (GB)
Title: Hydraulically driven hammer system
IPC: B25D9/12
Filed: 1975-09-16
Abstract: 1492698 Pile drivers RAYMOND INTERNATIONAL Inc 16 Sept 1975 [19 Sept 1974] 38062/75 Heading B3H A hydraulically driven hammer system comprises a hydraulic piston and cylinder assembly, a massive ram 42 connected to a movable part of the assembly, e.g. a cylinder 42A, co-operating hydraulic elements of a drive valve assembly 54 including an inner element, e.g. a valve spool assembly, Fig. 3 (not shown), on an outer element or housing having a chamber (104) in which the inner element is free to slide, the chamber being maintained at a first hydraulic pressure and the inner element having a control portion (130) which separates the chamber from a region maintained at a second hydraulic pressure, a pilot conduit or port (80) opening on to the control portion (130) to expose it to both hydraulic pressures alternately as the ram reciprocates, and hydraulic switching means responsive to changes in pressure within the pilot conduit for actuating the reciprocating movement of the ram. The ram 42 and cylinder 42A are movable over a fixed piston portion of an outer casing 14. A portion 32 of the piston divides the interior of the cylinder into chambers 50, 52. The chamber 50 is maintained at all times at the first hydraulic pressure by a pump 58 via conduits 84, while the chamber 52 is alternately maintained at the first or second hydraulic pressures, the second pressure being lower than the first, by the main drive valve 54. The pump 58 supplies fluid under pressure to the chamber 52 and as the piston lower stem portion 34 is smaller in diameter than the upper stem portion 30, the cylinder is driven downwards until it impacts an anvil 20. The impact is transmitted to a pile 24 while the fluid in the chamber 50 is exhausted to a high pressure accumulator. At the bottom of its stroke the cylinder closes the conduit 84 and opens a conduit 46, which opens the conduit to the interior of an outer casing 14. This is filled with fluid at the second pressure, which then actuates a pilot valve 56 via conduits 46, 40, 94, to switch over the main drive valve 54 so as to connect the conduit 70 and hence the lower chamber 52 to a drain 60. The pressure in the chamber 50 raises the cylinder and when the conduit 40 is again in communication with the chamber 50, the valve 54 is once more switched to supply fluid from the pump to the chamber 52. This preferably occurs at about half way of the ram travel, its inertia causing it to complete its upward stroke, and at the same time a large surge of pressure in the system is avoided. The valve 54 is held in the Fig. 1 position by the application of pump pressure to a connection 82 and is moved to its opposite position by applying drain pressure to the connection 82 by switching the pilot valve 56. This valve is switched by the alternate application of pump and drain pressure through the conduit 94 to an input 92. Feedback is supplied via a drain pilot line 72 and a drive pilot line 76 to provide light latching of the drive valve 54. The connections to inputs 88, 90 of the pilot valve 56 balance the valve for easy movement from one position to the other and accommodate the fluid displacement accompanying actuation of the valve.