Automatic load sensing vacuum valve

A vacuum lifting system comprising vacuum generating means, a lifting member, and vacuum conduit means connecting the vacuum generating means and the lifting member, the lifting member comprising a vacuum pad having a plurality of orifices communicating with the vacuum conduit means and being so constructed and arranged that when the vacuum pad is in contact with a load surface of predetermined characteristics, application of vacuum causes a vacuum seal to be formed with the load surface at each pad orifice which is fully covered by the load surface, the vacuum generating means when activated causing a predetermined initial flow rate of air along a flow path from the vacuum pad orifices through the vacuum conduit means, which rate is reduced to effectively zero when a vacuum seal has been established, wherein the improvement comprises a valve positioned at each vacuum pad orifice in the air flow path from that orifice to the vacuum conduit means, each said valve comprising:

• a) a two-piece housing defining a substantially cylindrical flow passage having an interior wall, a load end in the direction of the vacuum pad orifice, a vacuum end in the direction of the vacuum conduit means, and an orifice at each of said ends, one piece of the housing having an internally threaded bore at one end and one of the vacuum end and load end at the other end, the second piece of the housing having one end externally threaded to sealingly mate with the internal threads on the first piece and having the other of the vacuum end and load end at its other end, the flow passage being defined when the two pieces are threaded together, whereby the length of the flow passage can be adjusted by screwing the second piece into the first piece to varying extents, the orifice at the vacuum end being substantially circular in cross section, the orifice at the load end being configured to include an axially centered cylindrical hole extending from the flow passage to the exterior of the valve body, a bevelled shoulder extending part way around the cylindrical hole at the interior end thereof, and an axially eccentric cylindrical relief depression formed in the valve body at the interior end of said cylindrical hole, the axis of the relief depression being parallel to the axis of said cylindrical hole, the inner wall of the relief depression being tangent to the inner wall of said cylindrical hole at one point on the circumference thereof, the relief depression depth being from the axial level of the radially outward end of the bevelled shoulder to a point past the axial level of the radially inward end of said shoulder;
• b) a substantially spherical air impermeable float member within the flow passage and freely movable therein, the float member being larger than either of the vacuum end and load end orifices, the diameter of the float member being such that when the float member rests at the load end of the flow passage the bevelled shoulder and relief depression of the load end orifice configuration provide a channel for air flow around the float member from the flow passage through the load end orifice;
• c) means causing the float member to assume a rest position at the load end of the flow passage when vacuum is not being applied;
• d) the float member being of such density that the initial flow rate of air upon activation of the vacuum generating means causes the float member to move from the rest position to the vacuum end of the flow passage at a predetermined rate of speed;
• e) the surface of at least one of the float member and the flow passage interior wall at the vacuum end orifice being sufficiently resilient, and the vacuum end orifice being so configured, that when the float member engages the vacuum end orifice under the influence of the initial flow rate of air the float member sealingly conforms to the flow passage interior wall at the vacuum end orifice to stop further air flow through the valve in the direction of the vacuum end and thereby maintain the vacuum;
• and
• f) the length of the flow passage being adjusted such that upon activation of the vacuum generating means with a vacuum pad orifice contacting and fully covered by the load surface a vacuum seal will be formed at that vacuum pad orifice before the float member reaches and engages the vacuum end orifice of the valve.