A system for transferring solid particles from a first environment at a first gas pressure to a second environment at a second gas pressure. The system comprises a first rotary valve having an inlet which is in fluid communication with the first environment, a second rotary valve having an outlet which is in fluid communication with the second environment, and an intermediate housing bounding an intermediate channel, of which an inlet is fluidly connected to an outlet of the first rotary valve and of which an outlet is fluidly connected to an inlet of the second rotary valve. The intermediate channel is fluidly connected to a third environment maintained at a third gas pressure. The third gas pressure is higher than both the first gas pressure and the second gas pressure or lower than both the first gas pressure and the second gas pressure.