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Is there any setting in a two-stage blower that can influence the output pressure?

Q: We have a two stage combustion air blower with backward inclined vanes.The rated output flow is 3900 cubic mtr/hr and the output pressure is 1300 mm of WG.At present the output pressure is not going above 750mm of WG.We have checked for leakages as well as for obstrution but found none. Is there any setting in the blower that can influence the output pressure?

A: Before suggesting methods of increasing the blower output pressure, the maintenance condition of the blower should be examined. Is the blower fouled? Are the vanes in good physical condition? Is the blower operating speed at the rated value? Has the blower been shutdown to verify the above conditions? If all of the above are satisfactory, several ideas may be tried. The most obvious would be a speed increase. The amount of speed increase needed can be approximated by taking the square root of the ratio of 1300/750 which would indicate approximately a 30% speed increase. This can be further considered only if the manufacturer can verify the impellers can safely operated at this higher value and that the drive arrangement will permit a speed increase. Another avenue to investigate is the system resistance of the blower output. If the system resistance is lower than the design value, a speed increase would also increase the flow by 70% which would probably exceed the driver output capability. Finally the burner side may be modified by increasing the flow resistance at the outlet which would bring the discharge pressure to the rated value at the rated flow.

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