A vacuum valve for use with a blow mold in an I.S. machine. When the blow molds close around a parison, vacuum is applied to the wall of the blow mold. At some time following the application of the vacuum, final blow will occur blowing the parison into a bottle. This vacuum will be applied until the parison has been blown into a bottle. During the period during which vacuum is applied but final blow has not started, vacuum is reduced by operating a needle valve in the vacuum line.