GB1252796A - - Google Patents

Abstract

1,252,796. Piston return devices in stapling machines &c. SIGNODE CORP. 27 May, 1969 [27 May, 1968], No. 26680/69. Heading B4C. In a pneumatically operated device e.g. a stapling machine, a piston 36, Fig. 1, is driven by compressed air, controlled by a spool valve 90, in a cylinder 34 connected by holes 63 with an annular chamber 62. This chamber is for containing compressed air to return the piston 36 when the space 82 above the piston is relieved by the valve 90. The spool valve 90, in the position shown in Fig. 1, closes the space 82 above the piston 36 from the compressed air in air inlet chamber 84, and connects the space 82 with the atmosphere through an outlet 112. The valve 90 is lowered by the differential action of the compressed air in the inlet chamber 84 whilst a ball valve 120 is held in its uppermost position by a trigger 110 to cut off the space 94 below the spool valve 90 from the compressed air. In its lower position the valve 90 closes the outlet 112 and allows compressed air to enter the space 82 causing the piston 36 and driver 38 to perform its drive stroke. Different embodiments comprise different constructions allowing the compressed air to enter the annular chamber 62. The piston 36 and annular chamber 62 have 0-rings 60, 70 mounted in grooves, either of which 0-rings may have notches cut out of its lower face, Fig. 6 (not shown), or may have projections on its lower face, Fig. 8 (not shown). These constructions allow compressed air to leak past the O- ring when it is resting on the lower edge of its grooves. In an embodiment in which the piston 0-ring has the notched construction, compressed air can leak past the piston 36 and into the annular chamber 62 during the downward stroke and whilst it is stationary at the bottom of the cylinder 34. However when the piston is returned by the compressed air below the piston and in the annular chamber 62 the O-ring 70 then abuts the upper edge of its groove. Channels 130, 132 are provided to remove any residual compressed air below the piston when at the upper end of the cylinder 34. In an embodiment in which the annular chamber O-ring has the notched construction, Fig. 11, compressed air passes through passages 332, 333, and around the O-ring 270 during the downward stroke of the piston and whilst it is stationary at the bottom of the cylinder. However the annular chamber is sealed when the pressure above the piston and 0-ring 270 is relieved. In a further embodiment, a passage (523), Fig. 12 (not shown), connects the annular chamber 62 with the inlet chamber 84 when the valve 90 is in its lower position, and is shut off from the compressed air when the valve 90 is in its upper position.