Ceramic-plate flow-control valve

In a flow-control valve comprising:

• a housing having a chamber into which opens a port;
• a ceramic valve plate fixed in the chamber over the port, formed with a throughgoing aperture aligned with the port, and having a substantially planar face;
• a ceramic control plate having a substantially planar face lying flatly on the valve-plate face and formed with a throughgoing aperture;
• and
• means for pivoting the control plate relative to the valve plate about an axis substantially perpendicular to and traversing the surfaces between
• an open position with the control-plate aperture overlapping the valve-plate aperture and
• a closed position with the control-plate aperture aligned axially with a portion of the valve-plate face and offset angularly from the valve-plate aperture and with the valve-plate aperture aligned axially with a portion of the control-plate face and offset angularly from the control-plate aperture,
• the improvement wherein
• one of the faces is formed in a region offset from the respective face portion with a shallow recess open toward the other face, the recess being located such that in the open position of the valve it opens parallel to the faces into the aperture of the plate of the other face and in the closed position of the valve it is axially closed by the face of the other plate.