Abstract: An abrasive block 1 used for scraping wet leaves, snow or ice from a rail R of a railway track in order to enhance traction, is urged onto the rail R by a piston 2 under oil-pressure within a cylinder 3. The pressure is created via a diaphragm 11 which separates the oil in the cylinder 3 from an air-chamber 12. Chamber 12 is supplied with air via a regulator 14, from the air-brake supply system 16 of the train, and has a dump valve 19 for dissipating air-pressure surges. A return spring 20 under the piston 2 is active in retracting the block 1 when air-pressure in the chamber 12 is reduced.