Mass flow controller and operating method thereof

Abstract

A mass flow controller having a shut off valve in a flow path body as an integral part. The mass flow controller minimize a dead space between the shut off valve and a mass flow control valve to reduce the amount of entrapped gas therein, thereby avoiding occurrence of overshoot in the initiation of the next mass flow control operation. In another aspect, a bypass passage is provided in the flow path body. The bypass passage bypasses a sensor flow path, a bypass flow path and a mass flow control valve which increase a flow resistance, and therefore, a large amount of purge gas can be passed through the bypass passage in a short time. In still another aspect, a sealing surface of a valve seat is made into coplanar with the top surface of the flow path body, thereby making the sealing surface and the top surface of the body possible to be simultaneously subjected to lapping finish. This enhances the parallel relation between the sealing surface and the top surface of the body and makes it easy to align the axis of an actuator with the axes of other parts.