Vacuum system

1. A vacuum system for evacuating a chamber of a metallurgical processing system, the vacuum system comprising:

the chamber;

a vacuum pumping arrangement for evacuating gas from the chamber;

a foreline connecting the vacuum pumping arrangement to the chamber, wherein the foreline is downstream of the chamber and upstream of the vacuum pumping arrangement;

a filter volume located in the foreline for filtering gas evacuated from the chamber along the foreline;

a by-pass line connecting the vacuum pumping arrangement to the chamber and arranged to by-pass the filter volume selectively dependent on monitored characteristics of the chamber or the vacuum system, wherein the by-pass line is downstream of the chamber and upstream of the vacuum pumping arrangement; and

a control device comprising a programmable logic device or computer, wherein the control device comprises control lines connected to a plurality of valves configured to control operation of the vacuum system to:

convey gas from the chamber to the vacuum pumping arrangement along the by-pass line at a first range of pressures to reduce a pressure of the chamber to a first predetermined pressure less than atmospheric pressure, wherein gas pumped through the by-pass line does not pass through the filter volume,

convey gas from the filter volume along the foreline and through the vacuum pumping arrangement to reduce a pressure of the filter volume to a second predetermined pressure less than the first predetermined pressure,

connect the filter volume to the chamber along the foreline in response to the chamber being at the first predetermined pressure and the filter volume being at the second predetermine pressure, wherein gas is conveyed from the chamber to the filter volume by a pressure differential established by the second predetermined pressure being less than the first predetermined pressure, and

convey gas from the chamber, through the filter volume, and along the foreline at a second range of pressures less than the first range of pressures.

2. The vacuum system of claim 1 , wherein the by-pass line is arranged to connect the vacuum pumping arrangement to the chamber selectively dependent on the pressure in the chamber.

3. The vacuum system of claim 1 or 2 , wherein the foreline is arranged to isolate the filter volume from the chamber and the vacuum pumping arrangement when the by-pass line connects the vacuum pumping arrangement to the chamber.

4. The vacuum system of claim 3 , wherein the foreline comprises a first isolation valve upstream of the filter volume for isolating the filter volume from the chamber and a second isolation valve downstream from the filter volume for isolating the filter volume from the vacuum pumping arrangement.

5. The vacuum system of claim 1 , further comprising a by-pass valve for selectively conveying gas along the by-pass line dependent on the pressure in the chamber.

6. The vacuum system of claim 1 , wherein the first range of pressures extends from atmosphere to the first predetermined pressure and the second range of pressures extends from a pressure less than the first predetermined pressure to a target pressure lower than the second predetermined pressure.

7. The vacuum system of claim 1 , further comprising a by-pass valve for selectively conveying gas along the by-pass line dependent on the pressure in the chamber, wherein the foreline comprises a first isolation valve upstream of the filter volume for isolating the filter volume from the chamber and a second isolation valve downstream from the filter volume for isolating the filter volume from the vacuum pumping arrangement, wherein, at the first range of pressures, the control device is configured to control the by-pass valve so that gas is conveyed from the chamber to the vacuum pumping arrangement along the by-pass line and to control the first and second isolation valves so that the filter volume is isolated from the chamber and the vacuum pumping arrangement, and wherein, at the second range of pressures, the control device is configured to control the by-pass valve and the first and second isolation valves so that gas is conveyed along the foreline and through the filter volume to the vacuum pumping arrangement.

8. The vacuum system of claim 2 , further comprising a by-pass valve for selectively conveying gas along the by-pass line dependent on the pressure in the chamber.

9. The vacuum system of claim 3 , further comprising a by-pass valve for selectively conveying gas along the by-pass line dependent on the pressure in the chamber.

10. The vacuum system of claim 6 , further comprising a by-pass valve for selectively conveying gas along the by-pass line dependent on the pressure in the chamber, wherein the foreline comprises a first isolation valve upstream of the filter volume for isolating the filter volume from the chamber and a second isolation valve downstream from the filter volume for isolating the filter volume from the vacuum pumping arrangement, wherein, at the first range of pressures, the control device is configured to control the by-pass valve so that gas is conveyed from the chamber to the vacuum pumping arrangement along the by-pass line and to control the first and second isolation valves so that the filter volume is isolated from the chamber and the vacuum pumping arrangement, and wherein, at the second range of pressures, the control device is configured to control the by-pass valve and the first and second isolation valves so that gas is conveyed along the foreline and through the filter volume to the vacuum pumping arrangement.

11. The vacuum system of claim 1 , further comprising a by-pass valve for selectively conveying gas along the by-pass line dependent on the pressure in the chamber, wherein the foreline comprises a first isolation valve upstream of the filter volume for isolating the filter volume from the chamber and a second isolation valve downstream from the filter volume for isolating the filter volume from the vacuum pumping arrangement, wherein, at the first range of pressures, the control device is configured to control the by-pass valve so that gas is conveyed from the chamber to the vacuum pumping arrangement along the by-pass line and to control the first and second isolation valves so that the filter volume is isolated from the chamber and the vacuum pumping arrangement, and wherein, at the second range of pressures, the control device is configured to control the by-pass valve and the first and second isolation valves so that gas is conveyed along the foreline and through the filter volume to the vacuum pumping arrangement.

12. The vacuum system of claim 11 , wherein the control device is configured to partially equalize a pressure between the chamber and the filter volume prior to conveying the gas from the chamber to the vacuum pumping arrangement through the foreline at the second range of pressures.

13. A method of evacuating a chamber of a metallurgical processing system, the method comprising:

isolating a filter volume in a foreline from the chamber and a vacuum pumping arrangement, wherein the filter volume is configured to filter gas evacuated from the chamber along the foreline;

evacuating, through a by-pass line connecting the vacuum pumping arrangement to the chamber, the chamber from atmosphere to a first predetermined pressure, less than atmosphere, with the vacuum pumping arrangement, wherein the by-pass line is arranged to by-pass the filter volume such that gas pumped through the by-pass line does not pass through the filter volume;

closing a by-pass valve at the first predetermined pressure to disconnect the by-pass line from the chamber;

evacuating the filter volume to a second predetermined pressure less than the first predetermined pressure with the vacuum pumping arrangement using the foreline;

connecting the filter volume to the chamber using the foreline, wherein gas is conveyed from the chamber to the filter volume by a pressure differential established by the second predetermined pressure being less than the first predetermined pressure; and

evacuating the filter volume and the chamber with the vacuum pumping arrangement below the second predetermined pressure.

14. The method of claim 13 , further comprising:

controlling the by-pass valve so that gas is conveyed from the chamber to the vacuum pumping arrangement along the by-pass line and controlling isolation valves so that the filter volume is isolated from the chamber and the vacuum pumping arrangement while the chamber is evacuated to the first predetermined pressure, and

controlling the bypass valve and the isolation valves so that gas is conveyed along the foreline and through the filter volume to the vacuum pumping arrangement while evacuating the filter volume and the chamber below the second predetermined pressure.