They are special unidirectional valves that, when suitably calibrated, allow a certain quantity of fluid to go through, afterwards, if the fluid continues to go through, they automatically close.
This type of valves has been studied to be fitted on cups and when the piece to be taken is missing or when there is a faulty grip of the cup or if there are some losses, they automatically close suction, thus avoiding the vacuum decay on the remaining cups which are taking the body.
They are made in anodized aluminium and, besides the series valves shown on this page, they can be supplied in other sizes and materials.