Diffuser

1. A centrifugal compressor comprising an impeller and a diffuser, wherein the compressor operates between a lower flow rate and an upper flow rate, fluid exits the impeller at a first flow angle at the lower flow rate and at a second flow angle at the upper flow rate, the difference between the first flow angle and the second flow angle is around 20 degrees, and the diffuser comprises a plurality of radial vanes having a blade count of between 15 and 20, a solidity of between 0.6 and 0.8, and a radius ratio of vane inlet to impeller outlet of less than 1.5 so as to provide positive stall-free pressure recovery between the lower flow rate and the upper flow rate.

2. The compressor of claim 1 , wherein the radial vanes have a stagger angle selected such that the angle-of-attack at the upper flow rate is zero.

3. The compressor of claim 2 , wherein the stagger angle and the second flow angle are substantially the same.

4. The compressor of claim 1 , wherein the difference in the lower flow rate and the upper flow rate is about 7 l/s.

5. The compressor of claim 4 , wherein the lower flow rate is about 5 l/s and the upper flow rate is about 12 l/s.

6. The compressor of claim 1 , wherein the second flow angle is between 50 and 65 degrees.

7. The compressor of claim 1 , wherein the impeller rotates at speeds in excess of 80 krpm at both the lower flow rate and the upper flow rate.

8. The compressor of claim 1 , wherein the radius of the impeller is no more than 50 mm.

9. The compressor of claim 1 , wherein the impeller is mounted to a shaft, and the shaft is mounted to the diffuser by a bearing assembly directly secured to the shaft and the diffuser.

10. The compressor of claim 1 , wherein the solidity is between 0.60 and 0.65.

11. The compressor of claim 1 , wherein the radius ratio is less than 1.2.

12. The compressor of claim 1 , wherein the vanes have a stagger angle between 50 and 65 degrees.

13. The compressor of claim 1 , wherein the diffuser comprises a hub, a perimeter wall that encircles the hub and a plurality of axial vanes, and wherein the radial vanes are provided on an upper surface of the hub, and the axial vanes extend between the hub and the perimeter wall.

14. A vacuum cleaner comprising a centrifugal compressor comprising an impeller and a diffuser, wherein the compressor operates between a lower flow rate and an upper flow rate, fluid exits the impeller at a first flow angle at the lower flow rate and at a second flow angle at the upper flow rate, the difference between the first flow angle and the second flow angle is around 20 degrees, and the diffuser comprises a plurality of radial vanes having a blade count of between 15 and 20, a solidity of between 0.6 and 0.8, a radius ratio of vane inlet to impeller outlet of less than 1.5 so as to provide positive stall-free pressure recovery between the lower flow rate and the upper flow rate.