AN APPARATUS FOR SUPPLYING DRIVE FLUID UNDER PRESSURE IN A FIRST MODE OF LOW PRESSURE AND LARGE VOLUME RATE AND A SUBSEQUENT SECOND MODE OF HIGH PRESSURE AND SMALL VOLUME RATE TO A FLUID-DRIVEN MECHANICAL DEVICE

摘要

A fluid-driven device, such as a hydraulic cylinder (A), which may be the cylinder of a hydraulic press, is driven in the preliminary movement before encountering mechanical resistance, such as from a workpiece to be pressed, from a low-pressure fluid source (P) through an injector (I) being driven by fluid from a high-pressure fluid source (M). When said mechanical resistance is encountered, causing back pressure in the conduit leading to the cylinder (A), the injector (I) ceases to function as such, and high-pressure fluid alone is supplied through the injector to the cylinder, a non-return valve (11) preventing flow into the low-pressure part of the system. With this arrangement, the flow to the fluid-driven device may be controlled by means of extremely simple apparatus, in the embodiment shown comprising only one moving part, viz. the movable valve member in the non-return valve (11). In a slightly more complicated embodiment (not shown), the injector is bypassed by a pressure-controlled valve in the high-pressure mode, thus avoiding the throttling effect from the injector's drive nozzle.