Vacuum workholder and valve means therefor

Claim 1

A VACUUM HOLDER COMPRISING: A HOLLOW BODY DEFINING AN ENCLOSED SPACE THEREIN; ONE FACE OF SAID BODY COMPRISING A VACUUM HOLDING SURFACE HAVING A PERFORATE STRUCTURE WHICH PROVIDES COMMUNICATION BETWEEN AMBIENT PRESSURE AND SAID ENCLOSED SPACE; A PLURALITY OF WALLS DISPOSED IN SAID BODY TO DIVIDE SAID ENCLOSED SPACE INTO A PLURALITY OF CHAMBERS; A SOURCE OF VACUUM COMMUNICATIVE WITH AT LEAST ONE OF SAID CHAMBERS; MEANS INCLUDING A PRESSURE OPERATED VALVE TO CONTROL INTERCOMMUNICATION BETWEEN EACH OF SAID CHAMBERS AND THE SUCCEEDING CHAMBER THERETO, BIASING MEANS TO NORMALLY CLOSE SAID VALVE AND MEANS OPERATIVE TO OPEN SAID VALVE WHEN THE DIFFERENCE IN PRESSURE BETWEEN A CHAMBER AND THE SUCCEEDING CHAMBER TO WHICH IT PROVIDES INTERCOMMUNICATION IS SUFFICIENT TO OVERCOME SAID BIASING MEANS; MEANS TO APPLY THE PRESSURE DIFFERENT BETWEEN THE LAST-MENTIONED CHAMBER AND THE AMBIENT PRESSURE TO SAID VALVE TO HOLD SAID VALVE IN THE OPEN POSITION INDEPENDENTLY OF THE DIFFERENCE IN PRESSURE BETWEEN CHAMBERS WHEN SAID LATTER-MENTIONED DIFFENTIAL IS SUFFICIENT TO OVERCOME SAID BIASING MEANS.