A powder circuit (36) for use in an apparatus (10) for producing three-dimensional work pieces by irradiating layers of a raw material powder with electromagnetic or particle radiation comprises a process chamber (12) accommodating a carrier (16) and a powder application device (14) for applying a raw material powder onto the carrier (16), the process chamber (12) being provided with a powder inlet (30) for supplying raw material powder to the powder application device (14) and a powder outlet (32) for discharging excess raw material powder from the process chamber (12). The powder circuit (36) further comprises a powder circulation line (34) connecting the powder outlet (32) of the process chamber (12) to the powder inlet (30) of the process chamber (12) and a conveying device (38) arranged in the powder circulation line (34) for conveying the raw material powder through the powder circulation line (34). A sensor arrangement (42) is adapted to detect at least one of a parameter characteristic of a powder supply to the conveying device (38) and a parameter characteristic of a powder discharge from the conveying device (38). A control unit (40) adapted to control operation of the conveying device (38) in dependence of at least one of the parameter characteristic of the powder supply to the conveying device (38) and the parameter characteristic of the powder discharge from the conveying device (38).