Roots-type blower rotor alignment method

1. A method comprising the steps of:

immobilizing an idler gear with reference to a housing of a Roots-type blower, the housing comprising a drive rotor fixedly disposed on a drive shaft therein, an idler rotor engaged with the drive rotor and fixedly disposed on an idler shaft therein, a drive gear rotatably disposed on the drive shaft, and the idler gear engaged with the drive gear and fixedly disposed on the idler shaft;

rotationally displacing the drive shaft in opposite directions to a first extent and a second extent of travel, wherein each extent of the travel is defined by direct contact of the drive rotor against the idler rotor;

positioning the drive shaft at a determined rotational angle between the first and second extents of travel; and

fixing the drive gear to the drive shaft while the drive shaft is positioned at the determined rotational angle.

2. The method of claim 1 , further comprising the steps of:

coupling a source of a test gas to an outlet port of the blower thereby establishing a first flow path from the source to the outlet port;

rotating the drive shaft in a forward-flow direction at a predetermined rate while allowing the test gas to flow into the outlet port;

measuring a pressure at a location in the first flow path at a plurality of rotational angles of the drive shaft;

identifying at least one characteristic of a curve of the measured pressure vs. the respective rotational angle;

comparing the at least one characteristic to at least one criterion; and

assigning a passing rating to a blower that satisfies the at least one criterion.

3. The method of claim 2 , further comprising the steps of:

releasing the drive gear of a blower that does not satisfy the at least one criterion;

positioning the drive shaft at a new determined rotational angle that is offset by an alternate reference compensation amount from an angle that is midway between the first and second extents of travel;

fixing the drive gear to the drive shaft while the drive shaft is positioned at the new determined rotational angle;

immobilizing the idler gear with reference to the housing; and

repeating the steps of claim 2 .

4. The method of claim 3 , wherein the steps of claim 3 are repeated in a series of trials with an incrementally changed alternate reference compensation amount for each trial until either the blower is assigned a passing rating or an indication is reached that no more trials are to be conducted and the blower is rejected.

5. The method of claim 2 , wherein the step of measuring a pressure comprises measuring the pressure at a sample rate, in samples per second, that is greater than or equal to a value that is twice a product of a rotation rate, in rotations per second, of the drive shaft and a combined number of lobes on the drive and idler rotors.

6. The method of claim 1 , wherein the determined rotational angle is midway between the first and second extents of travel.

7. The method of claim 1 , wherein the determined rotational angle is offset by a predetermined reference compensation amount from an angle that is midway between the first and second extents of travel.

8. The method of claim 1 , further comprising the step of:

preloading the engagement of the drive gear with the idler gear.