a cell of a recuperator has a passage therein having a first end and a second end . in use a fluid passes through the passage under pressure . the cell must be tested to determine an operational efficiency or leakage within the passage . a pair of sealing mechanisms is positioned at a respective one of the first end and the second end of the passage . a vacuum is pulled across the passage and a rate of leakage is monitored to define an operational cell and a failed cell .