Speed valves for scrap and demolition shears connect the bottom and rod sides of their cylinder by means of valve pistons in the speed mode position. As soon as the shear hits material, the pressure increases. At a certain pressure, the valve spool switches to the power mode by connecting the rod side to the return.
In many hydraulic applications, high return pressures cause unnecessary energy losses or even performance losses. As a result, the full power is not available at the tool, and in some cases the pump is swung back by the power control, so that speed losses must also be accepted. If cylinders are used in the attachment tool, volume flows quickly occur on the bottom side that double the max. pump volume flow. The main control valves are not necessarily designed for this. These losses can be significantly minimized by an additional direct relief to the tank by means of a 3/3 directional control valve. A relief of e.g. 30 bar at 400 l/min volume flow creates more than 20 kW additional power at the die or correspondingly reduced losses. The valve thus operates as a bypass valve to the main control block.
