A metering device for granular material, includes a housing that can be arranged inside a container for the granular material. The housing has at least one inlet for the granular material and an outlet, which outlet can be closed by a sealing element. The sealing element is arranged on a metering piston, which is preloaded by a spring and can be moved axially in a compressed-air cylinder, wherein a compressed-air connection is provided on the compressed-air cylinder such that the metering piston can be moved against the spring by compressed air and the outlet can be opened, and the spring has an at least two-stage design such that the stroke of the metering piston can be changed at least in two stages by varying the compressed air.

A fluid control device includes a first conduit having a first end and a second end, and a first fluid that moves within the first conduit between the first end and the second end. The first conduit includes an interior surface defining a cavity of the first conduit. The fluid control device includes a second conduit having a third end and a fourth end, and a second fluid that moves within the second conduit between the third and fourth ends. At least a portion of the second conduit extends within the cavity of the first conduit. The first fluid is separate from the second fluid as the first fluid moves within the first conduit and the second fluid moves within the second conduit.

A method and an assembly for monitoring the fill level of a sandbox in a sanding system of a rail vehicle. The sandbox is connected to a pipe via a sand-conveying system. The sand-conveying system is controlled with a compressed air pulse in such a way that, with each compressed air pulse, a known quantity of sand is extracted from the sandbox and delivered in the form of a sand/compressed air mixture via the pipe into a wheel-rail gap of the rail vehicle. A control system of the rail vehicle determines a number of compressed air pulses used for operation, determines the quantity of sand applied by way of the number of compressed air pulses, and determines the current sand fill level of the sand container based on a previously known sand fill level of the sand container and the quantity of sand applied.