the upper portion of the main chamber 82 additionally the sealing ring 116 provides added friction to control the pump 39 s piston action when drawing purged ink and air through pump 50 during priming as described further below the pump 50 also has a piston 120 which may be a hollow generally cylindrical member the piston 120 includes a tapered ram portion 122 which is sized to be received within bowl 112 of washer 110 above the ram 122 the piston 120 has a shoulder portion 124 which sits upon the land 114 of washer 110 opposite the ram end 122 the piston has a cap receiving end 125 which has two opposing notches therethrough one of which is shown as notch 126 for receiving hook members 128 of plunger 52 a leaf spring member 130 is used to retain the piston 120 within the pump cover 90 as best shown in fig5 the cover 90 has a sleeve member 132 which is internal to and extends downwardly from the cover head 92 the sleeve 132 defines an upwardly extending slot 134 sized to receive the retaining spring 130 the spring 130 has a retaining protrusion 135 which is received within recesses 136 and 138 of piston 120 to retain the piston within the pump body 70 to assure that the recesses 136 138 are engaged.