Initially (before getting gouged up), even with a single whole zone uncovered on a single pump, the vac was high enough that the relief valve was already open. Covering the unused area within a zone when it’s in this regulated vac mode should not actually increase the vacuum at the pump, just open the relief valve more, but in practice it does improve the hold as it limits the air bleeding sideways in and under the bed.
With the relief valve is already open running on one pump to limit the vacuum, then turning on the second (which also has its own relief) should not increase the vacuum.
When would the second pump be used? I’m sure with multiple zones open and uncovered, the single vac’s relief valve will close and its vac will go down so the second pump could then increase the vac, but if you have that much uncovered area then you should cover it, which should then reach the vac relief limit on a single pump, right? Or is a substantial amount of air flowing through the area of the stock itself creating more work for the pump?
Regular 22"x48" posterboard is very easy to use for covering unused area. It can be peeled off the bed even with peak vac underneath, and- very important- unlike plywood or cardboard, it overlaps without making a gap along the seam. And light/cheap/reusable.
I talked with @jamesfreeman about putting a holder on the back of the control center to keep posterboard handy.
How do we know we’re at ~300mbar? Can we install a vac gauge to see how it’s performing?