Rotary positive displacement blower having a diverging outlet part

A rotary positive displacement blower for producing a flow fluid, said blower including:

• a housing having a rotor chamber, an inlet port and an outlet port
• a first rotor located in said rotor chamber, said first rotor having a plurality of lobes and being rotatable about a first axis in a first direction of rotation, said first rotor forming a plurality of first pockets, each said first pocket being located between adjacent lobes of said first rotor, each said first pocket adapted to rotate into fluid communication with said inlet port to receive fluid through said inlet port and to rotate into fluid communication with said outlet port to deliver fluid through said outlet port as said first rotor rotates;
• and
• a second rotor located in said rotor chamber, said second rotor having a plurality of lobes and being rotatable about a second axis in a second direction of rotation which is opposite to said first direction of rotation, said second rotor forming a plurality of second pockets, each said second pocket being located between adjacent lobes of said second rotor, each said second pocket adapted to rotate into fluid communication with said inlet port to receive fluid through said inlet port and to rotate into fluid communication with said outlet port to deliver fluid through said outlet port as said second rotor rotates;
• said outlet port of said housing having a first end located generally adjacent said first rotor and a second end located generally adjacent said second rotor,a first edge extending from adjacent said first end in a first plane which is generally perpendicular to said first and second axes of said rotors, a second edge extending from adjacent said second end in a second plane which is generally perpendicular to said first and second axes of said rotors and generally parallel to and spaced apart from said first plane a third edge which extends from adjacent said first end to said second edge and a fourth edge which extends from adjacent said second end to said first edge.
• said third edge including a first edge portion extending from adjacent said first end of said port towards said second edge such that the width of said port between said first edge portion and said first edge increases at a first rate of change, a second edge portion which extends from said first edge portion towards said second edge such that the width of said port between said second edge portion and said first edge increases at a second rate of change which is greater than said first rate of change and a third edge portion which extends from said second edge portion towards said second edge such that the width of said port between said third edge portion and said first edge increases at a third rate of change which is greater than said second rate of change,
• whereby the width of the portion of said outlet port which is in fluid communication with said pocket of said first rotor is initially relatively small, thereby providing a relatively low rate of fluid flow through said outlet port, and increases in size as said first rotor rotates.