Non-return valve for an injection moulding machine, comprising: - a main body in which at least one melt duct that runs between at least one melt duct entry opening of the main body and at least one melt duct exit opening of the main body is configured, comprising - a closing body that is mounted so as to be movable relative to the main body and in an open position is moved away from the melt duct exit opening that faces said closing body in such a manner that an exit of a plasticized melt from the melt duct exit opening is possible, and in a shut position is moved in front of the melt duct exit opening that faces said closing body in such a manner that an exit of a plasticized melt from the melt duct exit opening is impossible, and - an actuator installation that is assigned to the closing body and by way of which an actuating force acting on the closing body is capable of being exerted or is exerted in such a manner that the closing body is moved to the shut position, wherein - the actuator installation comprises at least one compression spring that is disposed within the main body and is coupled to the closing body, by way of which compression spring the actuating force acting on the closing body is exerted, wherein - the actuation installation comprises a bolt that couples the closing body to the main body and is mounted so as to be movable relative to the main body, wherein the compression spring is disposed on a bolt portion of the bolt that is located within the main body, characterized in that the bolt in the region of that end thereof that faces away from the closing body is provided with a detent face by way of which detent face said bolt in the shut position bears on a first counter-detent of the main body, and/or in that the bolt in the region of that end thereof that faces away from the closing body is provided with a detent face by way of which detent face said bolt in the open position bears on a second counter-detent of the main body. - a main body in which at least one melt duct that runs between at least one melt duct entry opening of the main body and at least one melt duct exit opening of the main body is configured, comprising - a closing body that is mounted so as to be movable relative to the main body and in an open position is moved away from the melt duct exit opening that faces said closing body in such a manner that an exit of a plasticized melt from the melt duct exit opening is possible, and in a shut position is moved in front of the melt duct exit opening that faces said closing body in such a manner that an exit of a plasticized melt from the melt duct exit opening is impossible, and - an actuator installation that is assigned to the closing body and by way of which an actuating force acting on the closing body is capable of being exerted or is exerted in such a manner that the closing body is moved to the shut position, wherein - the actuator installation comprises at least one compression spring that is disposed within the main body and is coupled to the closing body, by way of which compression spring the actuating force acting on the closing body is exerted, wherein - the actuation installation comprises a bolt that couples the closing body to the main body and is mounted so as to be movable relative to the main body, wherein the compression spring is disposed on a bolt portion of the bolt that is located within the main body,