Thursday, May 19, 2011

Working Principle of Twin Lobe Rotary Air Blower

Basic Twin Lobe Rotary Air Blower :

Everest Twin Lobe Rotary Air Blowers belong to the category of Positive Displacement Blowers. They consist of a pair of lobes, rotating inside a properly shaped casing, closed at ends by side plates. The drive lobe is connected to the driven lobe, through a pair of gears & they always rotate in opposite directions. As the rotors rotate, air is drawn into inlet side of the cylinder casing & forced out from the outlet side against the system pressure. With each revolution, four such volumes are displaced.

The air which is forced out is not allowed to come back due to small internal clearance within the internals of the machine except a very small amount called 'SLIP'. There is no change in the volume of air within the machine but it merely displaces the air from the suction end to the discharge end, against the discharge system resistance. Since the lobes run within the casing with finite clearances, no internal lubrication is required. The air thus delivered is 100% Oil Free. These blowers deliver, practically, a constant flow rate independent of the discharge pressure conditions. To illustrate further, let us consider a case when the discharge of a blower is connected to the bottom of a tank, having water to a depth of 'H' mm. The air discharged out of the blower accumulates in the discharge line until sufficient pressure is built (slightly over 'H' mm of WG), when it starts to escape out. The system resistance or the static load on the blower is thus 'H' mm of WG. The power consumed by the blower depends upon the flow rate and the total pressure head on the blower. A blower is capable of resisting high pressures but the mechanical limitations arising due to increased power intake, temperature rises and increase in 'SLIP' restricts the working pressure head to about 7000 mm WG for Air Cooled Blowers and 10,000 mm WG for Water Cooled Blowers in single stage operation. The blowers are generally selected for the maximum system pressure which they may encounter during operation & the prime mover is selected accordingly.

When in operation, the blower offers a considerable power saving since the power consumed by it depends upon the actual working pressure under which it operates and not the rated pressure. Consider a case when Everest Twin Lobe Rotary Air blower is selected for an application requiring a capacity of 'Q' m3/hr at 'H' mm of WG at which the power is specified as 'P' KW. Under the rated condition it would consume 'P' KW, but if the system back pressure falls from the rated/design value, the blower automatically starts working under lesser head & power requirement falls accordingly. These salient features make Rotary Air Blowers a versatile machine. They are ideal for applications requiring Constant Flow Rate at Varying Discharge Pressures.