I am working with a piece of equipment that has a vacuum sealed chamber. The outer wall (ring) of the chamber is shown in the image below. This ring is bolted to a bottom plate and a top plate is raised up and down using pneumatics. When the chamber is sealed the differential pressure between the inside and outside is nominally maintained at 10 psid. The system also has a laminar flow meter and once vacuum is pulled and the chamber is for the most part isolated, we can read about 1.5cc/min flow (leakage) in the chamber. Maximum flow readings for all other system components other than the chamber seal is below 0.0.03 cc/min, so I am convinced the issue is with the sealing of the chamber.
In the image can be seen a gland for an o-ring. This is an existing design, not of our own, so only minimal alterations to the design may be allowed. We will be looking at the flatness and finish on the top plate, but there has always been some variability on leakage from cycle to cycle.
So, this is my question... What is the likelyhood that adding a second o-ring in series with the first, with a minimal gap between them, may reduce the total leakage rate of the chamber?