Sheet feeding apparatus and method

Sheets are fed from the top of a stack (12) by a continuously rotating vacuum wheel (40). After the leading edge of a just-fed sheet is detected, a control circuit (110) de-energizes valve means (92) whereby the wheel (40) is effectively disconnected from a source of vacuum (90). Indicia borne on the just-fed sheet is read using a probe (23). If the indicia indicates that the just-fed sheet is related for grouping purposes to previously-fed sheets, the control circuit (110) energizes valve means (92) whereby vacuum is applied to the wheel (40) for the feeding of a further sheet. If the indicia indicates that the just-fed, just-read sheet is not related to previously-fed sheets, the control circuit (110) does not energize the valve means (92) for the feeding of a further sheet until the control circuit (110) receives an indication that all previously-fed sheets have been grouped and discharged onto an insert track (32). The valve means (92) comprises two electrically-actuated solenoid valves (94, 96) connected in parallel between the source of vacuum (90) and a vacuum transfer block (42).