Patent ID: 8083854

Claim:
A vacuum pumping circuit ( 14 ) for a machine for treating containers ( 12 ) by depositing an internal barrier coating by means of a microwave-generated plasma, comprising: an upper chamber ( 34 ) and a lower chamber ( 36 ) that communicate via a connecting orifice ( 38 ), the lower chamber ( 36 ) being connected to a cavity ( 20 ) and the upper chamber ( 34 ) to a vacuum pump ( 28 ) designed to evacuate the cavity ( 20 ) until the pressure in the cavity ( 20 ) reaches a specified value termed the final value (pF ext ), and a valve ( 40 ) guided in a sliding manner along an essentially vertical axis (A 1 ) in a corresponding opening ( 44 ) in the upper transverse wall ( 46 ) of the upper chamber ( 34 ), between a closed lower axial position, in which the valve head ( 42 ) of the valve ( 40 ) closes the connecting orifice ( 38 ), and an open upper axial position, the valve ( 40 ) having a valve stem ( 48 ) that extends axially up out of the upper chamber ( 34 ), the valve stem ( 48 ) being connected to means ( 50 ) for moving the valve ( 40 ) at least to its open position, wherein the valve stem ( 48 ) is provided with a section forming a piston ( 52 ) which constitutes the mobile upper wall of a control chamber ( 54 ) communicating with the upper chamber ( 34 ), the piston ( 52 ) having an upper face ( 56 ) permanently at atmospheric air pressure and a lower face ( 58 ) on which the pressure is that present in the control chamber ( 54 ), in such a way that when the pressure in the lower chamber ( 36 ) reaches the final value (pF ext ), the valve ( 40 ) is kept closed by the action of the pressure differential across the two faces ( 56 , 58 ) of the piston ( 52 ), and wherein the upper transverse wall ( 46 ) comprises an annular spacer ( 60 ) that is fitted axially between the opening ( 44 ) and the control chamber ( 54 ), and open channels ( 78 ) extending axially through said annular spacer ( 60 ) with, at one distal end of the open channels, an opening to the control chamber ( 54 ) and, at an opposite distal end, an opening to the upper chamber ( 34 ), the open channels isobarically connecting together the control chamber ( 54 ) and the upper chamber ( 34 ).