24 within the spacer element and air is exhausted through multiple orifices 30 from chamber 28 when the interior volume contracts the opposite situation occurs the volume sums of chambers 24 and 28 always equal unity and comprise the total volume of the interior longitudinal chamber as was noted earlier the dimensions of separator element 18 and the size of interior chambers 24 and 28 can be determined by the maximum contraction or expansion expected under conditions of use this can be readily calculated fig8 shows the preferred placement of multiple orifices 26 and 30 these are formed at longitudinal intervals along the first and second faces orifices 26 will align with similar orifices in the strip 37 fig2 when this element is used it is very desirable that the gas volume within the window be adjusted to the average expected environmental situation prior to installation of the windows thus if a window was manufactured in a sea level environment such as seattle and installed in a high elevation environment such as denver it might be necessary to release some of the internal gas within the window to equalize the pressure with that pressure which is normal at the use location when the opposite situation prevails it might be necessary to add internal volume gas to a window that might have been manufactured at a high elevation location for use at a sea level environment this can be conveniently done by a tool such as the one shown in fig5 here a volume equalizing needle 40 is seen to have a shank 42 with an internal bore 44 a threaded end 46 can be connected to a metered source of dry gas such as nitrogen to.