Powered work-clamping devices

Claim 1

A FLUID-ACTUATED SWING CLAMP COMPRISING, A PIVOTALLY MOUNTED CLAMPING ARM, A RAM FOR MOVING THE ARM TO A WORK-CLAMPING POSITION, SAID RAM HAVING A PRESSURE CHAMBER, A HYDRAULIC BIAS CONTROL VALVE FOR THE HYDRAULIC FLUID PRESSURE FOR THE RAM, MEANS RESPONSIVE TO THE WORKING MOVEMENT OF THE ARM TO REMOVE THE BIAS LOADING OF THE RAM PRESSURE CHAMBER DURING AN INITIAL CLAMPING MOVEMENT OF THE ARM, SAID MEANS BEING EFFECTIVE TO RESTORE THE BIAS PRESSURE LOADING DURING A FINAL UNCLAMPING MOVEMENT OF THE ARM, WHEREBY FULL HYDRAULIC PRESSURE IN THE SYSTEM IS AVAILABLE FOR CLAMPING WITHOUT DIFFERENTIAL LOSS FROM SUCH UNLOADING, SAID CONTROL VALVE BEING MOVABLE RELATIVE TO ITS SEAT WITH THE MOVEMENT OF THE RAM BEING SUCH AS TO BE UNSEATED AND RESEATED RESPECTIVELY WITH THE INITIAL OR ENGAGING MOVEMENT AND FINAL RETURN MOVEMENT OF THE RAM, THE CONTROL VALVE BEING NORMALLY MOUNTED ON AND COAXIAL WITH THE RAM WITH LIMITED BIASLOADED RELATIVE MOVEMENT, A LEAK-AWAY BY-PASS IN THE CONTROL VALVE FITTED WITH A NON-RETURN VALVE AND RELEASING RESIDUAL PRESSURE IN THE RAM CYLINDER AFTER THE BIAS-VALVE HAS BEEN RESEATED.