Bonded abrasive tools, having novel porous structures that are permeable to fluid flow, comprise a relatively low volume percentage of abrasive grain and bond, and a relatively low hardness grade, but are characterized by excellent mechanical strength and grinding performance. The feeder includes a hollow tube containing feed. When in a parallel mode, the second output is coupled to the first output in order to increase the first current supplied to the first load and decrease the second current supplied to the second load. The valve may be used as a fuel injector in an internal combustion engine, such as in a mixture-compressing, spark-ignition internal combustion engine.