Pinch valve, comprising: - a hose guide aligned along a hose guide axis, - a clamping member with • a plunger slidingly mounted along a plunger guide axis aligned perpendicularly to the hose guide axis, and • two clamping jaws jointly forming a clamping mouth and being articulated to the front end of the plunger that faces the hose guide and being configured to pivot in opposite directions about a pivot axis aligned in parallel to the hose guide axis, and - an abutment arranged on a side of the hose guide opposite the clamping member, wherein the clamping member is configured to advance towards the abutment to close the pinch valve so that, as the clamping member advances, the clamping mouth opens and the mouth base of the clamping mouth presses a hose guided in the hose guide - if present - against the abutment and thereby narrows the lumen of the hose, and the clamping jaws are coupled to a mechanical constraint such that a retraction of the plunger starting from a maximally advanced clamping position of the clamping member produces a pivoting movement of the clamping jaws in a closing direction of the clamping mouth, characterized in that the clamping member is mounted between two side walls of a valve housing that extend in parallel to the hose guide axis and to the plunger guide axis, each of the side walls having a step that extends in parallel to the hose guide axis and that recedes with respect to the advancing direction of the plunger, wherein the clamping jaws, upon displacement of the clamping member, move over said steps with their outer sides that face away from the hose guide bearing against the side walls, wherein the mechanical constraint is achieved unidirectionally by the interaction of the outer sides of the clamping jaws with the stepped side walls. - a hose guide aligned along a hose guide axis, - a clamping member with • a plunger slidingly mounted along a plunger guide axis aligned perpendicularly to the hose guide axis, and • two clamping jaws jointly forming a clamping mouth and being articulated to the front end of the plunger that faces the hose guide and being configured to pivot in opposite directions about a pivot axis aligned in parallel to the hose guide axis, and • a plunger slidingly mounted along a plunger guide axis aligned perpendicularly to the hose guide axis, and • two clamping jaws jointly forming a clamping mouth and being articulated to the front end of the plunger that faces the hose guide and being configured to pivot in opposite directions about a pivot axis aligned in parallel to the hose guide axis, and - an abutment arranged on a side of the hose guide opposite the clamping member, wherein the clamping member is configured to advance towards the abutment to close the pinch valve so that, as the clamping member advances, the clamping mouth opens and the mouth base of the clamping mouth presses a hose guided in the hose guide - if present - against the abutment and thereby narrows the lumen of the hose, and the clamping jaws are coupled to a mechanical constraint such that a retraction of the plunger starting from a maximally advanced clamping position of the clamping member produces a pivoting movement of the clamping jaws in a closing direction of the clamping mouth, characterized in that the clamping member is mounted between two side walls of a valve housing that extend in parallel to the hose guide axis and to the plunger guide axis, each of the side walls having a step that extends in parallel to the hose guide axis and that recedes with respect to the advancing direction of the plunger, wherein the clamping jaws, upon displacement of the clamping member, move over said steps with their outer sides that face away from the hose guide bearing against the side walls, wherein the mechanical constraint is achieved unidirectionally by the interaction of the outer sides of the clamping jaws with the stepped side walls.