Abstract: An apparatus and a method for evacuating a process chamber by a dry pump and then shutting down the pump without back steam and high pressure safety problems are disclosed. In the apparatus, a conduit is provided for connecting in fluid communication between a process chamber and a dry pump, two gate valves are provided in the conduit with one mounted adjacent to the process chamber and the other adjacent to the dry pump. A pressure relief valve is provided and mounted to bridge over an inlet and an outlet of the second gate valve such that any pressure build-up in the conduit upstream of the second gate valve can be avoided for preventing injury to a machine operator. The back steam problem can be effectively prevented when the dry pump is shut down simultaneously with the closing of the first and the second gate valves. The pressure relief valve may be pre-set to operate automatically when a differential pressure larger than 0.33 psi is detected.