A metering slide for fine-grained solids for gastight closing and cross-section-variable opening of vessels and piping in pneumatic conveying systems. A sliding plate provided with a metering opening is moved between two slide rings by a drive in a compression-proof slide casing. The intake side slide ring opening has a predetermined nominal width between 1/10 and 1/3 of the outside diameter of the slide ring. The discharge side slide ring has an inside diameter corresponding to 3 times to 10 times the nominal width of the intake. The slide casing is filled with a lubricant which is under a pressure equal to or higher than the operating pressure of the penumatic conveying system.