Cleaning of a 3D printed article

An apparatus for cleaning an article comprising internal channels, the apparatus comprising:

• a pump configured to pump cleaning fluid through the internal channels to thereby remove particles from the internal channels into the fluid;
• a sensor arranged to generate a magnetic field, wherein the sensor is configured to detect, in fluid being pumped past the sensor, the presence of particles in the fluid having a different magnetic permeability than the fluid, by detecting perturbation of the magnetic field caused by the particles;
• and
• a fluid circuit including the pump, wherein the pump defines an upstream position of the fluid circuit and is configured to pump a fluid through the circuit;
• wherein the fluid circuit comprises a connection downstream of the pump, the connection being configured to fluidly attach to an article comprising internal passages;
• wherein the sensor is located downstream of the connection;
• wherein the fluid circuit comprises a stage configured to vibrate the article;
• wherein the fluid circuit comprises valves configured to constrain fluid to the internal channels of the article when the article is vibrated on the stage.