Vacuum pump

1. A vacuum pump comprising:

a rotor;

an orientation sensor for sensing an orientation of the vacuum pump; and

a processing unit that is configured to use the sensed orientation to determine that the vacuum pump is in a permissible or an impermissible orientation and is configured to perform at least one of:

controlling the rotor such that a rotational speed of the rotor is reduced while allowing the vacuum pump to continue to operate in the impermissible orientation;

in the permissible orientation, controlling the rotor to allow the vacuum pump to continue to operate for a period of time corresponding to a predetermined maintenance event, and in the impermissible orientation, controlling the rotor to allow the vacuum pump to continue to operate for another period of time that is less than the period of time corresponding to the predetermined maintenance event;

controlling the rotor to allow the pump to continue to operate in the impermissible orientation and controlling a display unit to display that the pump is in the impermissible orientation and to display a length of time that the vacuum pump is allowed to operate in the impermissible orientation.

2. The vacuum pump as claimed in claim 1 , comprising a pump housing and wherein the orientation sensor is fixed relative to the pump housing.

3. The vacuum pump as claimed in claim 1 , wherein the orientation sensor is a tilt sensor.

4. The vacuum pump as claimed in claim 1 , wherein the orientation sensor is an accelerometer.

5. The vacuum pump as claimed in claim 1 , comprising a lubrication circuit for supplying lubricant to relatively moving surfaces of the vacuum pump, a supply of lubricant being dependent on the orientation of the vacuum pump.

6. The vacuum pump as claimed in claim 5 , wherein the lubricant circuit is arranged such that gravitational force causes lubricant to flow along at least a portion of the lubrication circuit only in said at least one permissible orientation of the vacuum pump.

7. The vacuum pump as claimed in claim 1 , wherein the rotor is supported for rotation by a drive shaft, a first bearing assembly for controlling movement of the rotor during rotation of the drive shaft, a back-up bearing assembly for limiting said movement of the rotor, wherein said orientation sensor is configured for sensing when said movement is limited by the back-up bearing assembly.

8. The vacuum pump as claimed in claim 7 , wherein said movement of the drive shaft is generally in the radial direction relative to the axis of the drive shaft.

9. The vacuum pump as claimed in claim 7 , wherein the back-up bearing assembly is arranged to limit said movement of the rotor by contact with the rotor or the drive shaft, and the sensor is arranged to sense each contact event between the back-up bearing assembly and the rotor or the drive shaft.

10. The vacuum pump as claimed in claim 7 , wherein the first bearing assembly is a non-contact bearing assembly which controls said movement of the rotor without contacting the rotor or the drive shaft.

11. The vacuum pump as claimed in claim 10 , wherein the first bearing assembly is a magnetic bearing assembly.

12. The vacuum pump as claimed in claim 7 , wherein the first bearing assembly is spaced from the rotor or the drive shaft by a distance which is greater than the distance which the back-up bearing assembly is spaced from the rotor or the drive shaft.

13. The vacuum pump as claimed in claim 7 , wherein the sensor is arranged to sense a force imparted to the rotor or drive shaft sufficient to cause the back-up bearing to limit said movement of the rotor resulting from the force.

14. The vacuum pump as claimed in claim 13 , wherein the sensor is an accelerometer.

15. The vacuum pump as claimed in claim 7 , wherein the sensor is fixed relative to a pump housing.

16. The vacuum pump as claimed in claim 7 , wherein the sensor is arranged to output a signal to a counter for counting a number of events that the back-up bearing assembly has limited said movement.

17. The vacuum pump as claimed in claim 16 , comprising an indicator for indicating to a user when the number of events exceeds a predetermined value predictive of a failure of the back-up bearing assembly.

18. The vacuum pump as claimed in claim 17 , wherein the indicator is the display for displaying the number of events.

19. The vacuum pump as claimed in claim 17 , wherein the indicator comprises a transmitter for transmitting the number of events to a remote location by wired or wireless connection.

20. The vacuum pump as claimed in claim 7 , wherein the sensor is arranged to sense a magnitude of a force imparted to the vacuum pump and associate the damage caused to the back-up bearing assembly dependent on the sensed magnitude.