a peripheral wall structure which surrounds the printhead nozzle array 70 a when the service module is in the park or engaged position as shown in fig1 the inner cap structure is fabricated of a relatively hard non resilient material to maintain a constant volume within the open space 230 e 5 even if the printer is subjected to vibration and shock maintaining a constant volume within this space minimizes or eliminates a pumping action on the nozzle array resulting from volume fluctuations as an alternate to an inner cap structure with a peripheral wall the structure 230 e 2 can be fabricated of a relatively hard solid non resilient material which is urged against the nozzle array of the printhead to simulate the tape applied to the nozzle array when shipped from the manufacturer there is essentially no air gap between the inner cap structure and the nozzle plate of the printhead in this case in the example of the special service module 230 e and even for the special service modules illustrated in fig6 9 the problem to be solved may be known before the printer is manufactured or shipped to the user and the software routines or algorithms for instructing.