formed in rotor r as rotor r rotates in a clockwise direction vane 53 slides outwardly in slot 53 a until it engages the inner stator wall 58 of stator s vanes 54 through 57 similarly slide outwardly in respective slots 54 a through 57 a in fig5 vanes 54 through 57 are illustrated as new vanes having little wear vane 53 is illustrated as having substantial wear thereto referring to vane 53 two pumping chambers chamber a and chamber b are formed between inner stator wall 58 and vane 53 chamber a is an inlet chamber at low pressure and chamber b is a pumping chamber beginning to compress incoming air thus chamber b can be said to be at high pressure rotor r is further provided with holes 53 b through 57 b drilled therein to connect inlet low pressure chamber a with an exhaust plenum of pump p via the drilled passageway through a rotor segment not shown the exhaust plenum interconnects chamber a and chamber b when vanes 53 through 57 have little to no wear even when fully extended in respective slots 53 a through 57 a the vane length is sufficient to cover respective holes 53 b through 57 b in fig5 vanes 54 a through 57 a have little wear and as each extends in its respective slot 54 a through 57 a holes 54 b through 57 b remain covered however vane 53 which is illustrated as being significantly worn has extended far enough in slot 53 a so that hole 53 b is uncovered since hole 53 b is uncovered air leakage occurs from pumping chamber b this leakage from the pumping chambers reduces pumping efficiency by at least partially equalizing pressure between.