The vacuum check valve with release check valve is used with a single vacuum cup so a non-porous, high value work piece won’t be immediately dropped if the system vacuum source is lost.
The vacuum trapped by the vacuum check valve will eventually leak down. The rate at which the vacuum diminishes will depend on the condition of all of the components in the vacuum system.
To increase the time delay interval, a volume chamber can be added to the auxiliary port. If the volume of the chamber is twice that of the internal cup volume, the time delay interval will be approximately tripled and so forth.