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Description of Driving Event:

Technicians were performing a maintenance operation on a Mazak CNC milling machine vacuum pump when a glass oil mist separator bowl burst. The subject bowl was attached to the discharge of a 3 hp Gast pump. This particular pump has the capability of producing 15 psi at the outlet if restricted. The rated pressure of the glass bowl is 5 psi, which is clearly marked with a warning regarding breakage. Prior to the incident, the pump had undergone overhaul and, after reinstalling the pump, the technicians operated it in order to circulate its lubrication oil. Once oil circulation was verified, the pump was restarted and the glass oil separator bowl ruptured. Fortunately, no one was injured by the broken glass. The technicians performing the task stated that there was no known restriction in the discharge piping downstream of the separator. It should also be noted that an identical separator is installed on the inlet of the vacuum pump. The incident prompted an investigation of other similar installations in the facility. The result was that a total of 3 machines are using the same oil separator configuration as the subject machine. These separators are factory installed and are standard equipment on these type of machines. To prevent injury from unanticipated glass fragmentation due to overpressurization of the oil separator, maintenance management personnel decided to install a wire cage around the pump discharge.