fig1 shows a wide format printer 1 of the type fed by a media roll 4 . however , as discussed above , for the purposes of this specification , a wide format printer is taken to mean any printer with a print width exceeding 17 ″ ( 438 . 1 mm ) even though most commercially available wide format printers have print widths in the range 36 ″ ( 914 mm ) to 54 ″ ( 1372 mm ). the print engine ( that is , the primary functional components of the printer ) are housed in an elongate casing 2 supported at either end by legs 3 . the roll of media 4 ( usually paper ) extends between the legs 3 underneath the casing 2 . a leading edge 8 of the media 5 is fed through a fed slot ( not shown ) in the rear of the casing 2 , through the paper path of the print engine ( described below ) and out an exit slot 9 to a collection tray ( not shown ). at the sides of the casing 2 are ink tank racks 7 ( one only shown ). ink tanks 60 store the different colors of ink that are fed to the printhead modules ( described below ) via a tubing system 10 . user interface 6 is a touch screen or keypad and screen for operator control and diagnostic feedback to the operator . for the purposes of this specification , references to ‘ ink ’ will be taken to include liquid colorant for creating images and indicia on a media substrate as well as any functionalized fluid such as infra red inks , surfactants , medicaments and so on . fig2 is a diagrammatic representation of components within the print engine . media feed rollers 64 and 66 unwind media 58 from the roll 4 . media cutter 62 slices the continuous media 58 to form a separate sheet 54 of desired length . as the media is being cut , it needs to be stationary within the cutter 62 ( so as not to create a diagonal cut ). however , the roll 4 is to keep rotating to maintain angular momentum . in light of this , the unwinder feed rollers 66 operate at a constant speed while the cutter feed rollers 64 momentarily stop during the cutting process . this creates a delay loop 68 between rollers 66 and 64 as the media bows upwards . after cutting , the continuous media 58 momentarily feeds through the cutter 62 faster than the speed of the unwinder feed rollers 66 to return the delay loop 68 to its initial position . the media sheet 16 feeds through a grit - coated drive roller 16 and over a fixed vacuum platen 26 . the vacuum holds the media path 54 flush with the top of the platen to accurately retain the media in the media path 54 . opposite the fixed vacuum platen 26 are five printhead modules 42 , 44 , 46 , 48 and 50 which span the width of the media path 54 . the printhead modules are not end - to - end but rather staggered with two of the printhead modules 44 , 48 upstream of the printhead modules 42 , 46 and 50 . immediately downstream of the fixed vacuum platen 26 is a vacuum belt assembly 20 . the vacuum belt assembly provides a second media transport zone ( the first being the input drive roller 16 ). the vacuum belt assembly 20 creates a movable platen that engages the non - printed side of the media 5 and pulls it out of the print zone 14 ( see fig3 ) once the trailing edge of the media 5 disengages from the input drive rollers 16 . a scanning head 18 is downstream of the vacuum belt assembly 20 . when a new printhead module is installed , a test print is fed passed the scanning head 18 . the dot pattern in the test print is scanned and the supervising driver pcb ( described below ) digitally aligns the print from each of the printhead modules . fig3 is a schematic representation of the platen assembly 28 . the five printhead modules 42 - 50 staggered across the 42 ″ wide media path 54 . the printhead modules are staggered because their respective service modules 22 can not be aligned flush end - to - end . drive mechanisms ( described below ) extend from the longitudinal ends of each service module 22 . furthermore , the printhead modules need to overlap with each other in a direction 17 transverse to the paper feed axis 15 . printing in the overlap between adjacent printhead modules is controlled by the supervising driver pcb to ‘ stitch ’ the print together without artifacts . fig4 shows the location of one of the service modules 22 embedded with the fixed vacuum platen 26 . their structure and operation is described more fully below . these modules can extend through the media feed path 54 to cap or wipe the nozzles on their respective printhead modules 42 to 50 . they can also retract away from the printhead modules to provide a spittoon , vacuum platen , and / or aerosol collector . staggering the printhead modules increases the size of the print zone 14 which is not ideal . maintaining a uniform printing gap ( the gap between the nozzles and the surface of the media substrate ) becomes more difficult as the area of the print zone increases . however , as the printhead ic &# 39 ; s ( described below ) have a narrow nozzle array ( less than 2 mm wide ) that prints five channels , the full color printhead assembly for 42 ″ wide media , has a print zone less than 129032 square mm ( 200 square inches ). in the particular embodiment described , the print zone 14 has a total area of 114 . 5 square inches . a relatively small print zone 14 allows the fixed vacuum platen 26 to be smaller and less force is required by the input drive roller 16 to push the media through the print zone . for a print zone less than 129032 square mm ( 200 square inches ), the vacuum pressure exerted on the media can be less than 0 . 2 psi . in the specific example shown , the fixed vacuum platen 26 operates a vacuum in the range of 0 . 036 psi to 0 . 116 psi . this equates to a normal force on the media of between 4 lbs and 13 . 5 lbs . the input driver roller 16 is a grit shaft that pushes the media into the print zone 14 . opposite the input drive roller 16 is an input drive pinch roller to ensure sufficient friction between the media surface and the surface grit of the input drive roller . the scanning zone 36 is the strip traversed by the scanning head 18 over the vacuum belt assembly 20 . the vacuum belts keep precise control of the media position during the optical scan . by scanning the print of a test dot pattern , the scanning head 18 sends feedback to the supervising driver pcb to align drop ejections from adjacent printhead modules , update a dead nozzle map , compensate for misfiring nozzles , and other purposes directed toward optimizing system print quality . the encoder wheel 24 is embedded in the fixed vacuum platen 26 between the two leading printhead modules 44 and 48 . the area between the leading printhead modules 44 and 48 is an unprinted location so the encoder wheel 24 can roll against an encoder pinch roller 38 . this also allows the media encoder to be as close as possible to the printheads , allowing for more accurate timing signals . the supervisor driver pcb uses the timing signal output from the encoder wheel 38 to time the drop ejections from the printhead modules . however , timing is also derived from encoders ( described in more detail below ) on the input drive shaft 16 and the vacuum belt drive shaft ( see below ) for periods when the media has not reached the encoder wheel 38 or the trailing edge has disengaged the encoder wheel 38 . the vacuum belt assembly 20 has a belt speed marginally higher than the media feed speed provided by the input drive roller 16 . however , the engagement between the input drive roller 16 and the media is stronger than the engagement between the media and the vacuum belts . consequently , there is slippage between the media and the belts until the trailing edge of the media disengages from the input drive roller . the vacuum belts provide a moving platen that engages one side of the media only so there is no risk to the print quality . furthermore , the period of transport across the vacuum belts provides the ink with drying time . the leading edge of the media 8 ( see fig1 ) is held flush on the belts by the vacuum so that the scanner head 18 can properly image the printed dot pattern . having the vacuum belt assembly 20 pulling the media from the print zone 14 is another mechanism by which the media is kept flush on the fixed vacuum platen 26 . in the wide format printer described below , the vacuum belt area , when printing 42 ″ wide media is 42 . 5 square inches . the vacuum pressure is between 0 . 036 psi and 0 . 45 psi which is relatively small . this keeps the normal force on the media below a maximum of 20 lbs . aerosol is collected using an upper aerosol collector 34 from above the media path 54 and the service modules 22 from below the media path . with the printhead modules ejecting droplets of less than 2 pico - liters at fast print speeds , there is a high production of aerosol which is misfired droplets that become airborne particulate . this needs to be removed to prevent aerosol build up on components and eventual smearing on the media surface . fig5 and 6 are perspectives of the wide format print engine 72 in its entirety . fig7 is an exploded perspective of the wide format print engine 72 . the major components of the print engine 72 are the upper path assembly 74 including the datum printhead carriage 76 , the lower paper path assembly 78 including the vacuum belt assembly 20 , the upper ink distribution assembly 80 including the ink bottles 60 and pinch valves 86 , and the lower ink distribution assembly 82 including the ink tanks 88 . fig8 is an exploded perspective of the lower paper path assembly 78 without the vacuum belt assembly 20 or the service modules 22 . the input drive shaft 16 and pinch roller 52 are supported between a left side chassis plate 96 and a right side chassis plate 98 . the bale feed roller 114 drives the media over the input paper guide 102 and through the nip between the input drive roller 16 and pinch roller 52 . vacuum table 88 is directly downstream of the input drive roller 16 . service apertures 108 in the vacuum table 88 house the five service modules 22 ( see fig5 ). the vacuum table 88 is mounted directly on a datum c - channel 100 mounted between the chassis plates 96 and 98 . vacuum blowers 94 create a low pressure beneath the vacuum table 88 to hold the non - printed side media . on both sides of the datum c - channel 100 is a left datum plate 90 and a right datum plate 92 . the left datum plate 90 has a single datum location 112 and the right datum plate has two datum locations 110 . the datum features on the printhead carriage ( described below ) sit in the datum locations 110 and 112 to hold the printhead modules 42 - 50 at the correct printing gap . latches 106 hold the upper paper path assembly 74 in position on the lower paper path assembly 78 . unlocking the latches 106 allows the upper paper path assembly 74 to be lifted up from the lower paper path assembly 78 and held in an elevated position by spring loaded gas struts 104 . fig9 is a perspective of the upper paper path assembly 74 . the chassis frame 126 holds the printhead carriage 76 and the scanner assembly 18 . at either side of the chassis frame 126 are gas strut mounting points 122 where the gas struts 104 ( see fig8 ) connect . the printhead carriage 76 is a housing for the five printhead modules 42 - 50 ( see fig3 ), their respective ink interfaces 124 and electrical connection units 120 . the rear wall 128 of the printhead carriage 76 has tubing apertures 116 for ink supply tubes . electrical cabling plugs into the cable sockets 124 on the top side of each electrical connection unit 120 . fig1 is a perspective of the printhead assembly 75 in which the printhead carriage 76 supports the five printhead modules 42 - 50 . also shown are the conventional xyz axes oriented in their usual manner in the field of printer design . the printhead carriage 76 is a machined extrusion with three datum features 130 fixed to the underside of the floor section 132 ( only the two right hand side datum features 130 are visible ). the floor section has apertures ( not shown ) to expose the nozzles on the printhead modules 42 - 50 to the media or the service modules 22 . the printhead modules ( described below ) abut the top side of the floor section 132 and use it as a z - datum . the datum features 130 sit in the left and right z datum point 110 and 112 ( fig8 ) fixed to the datum c - channel 100 . the datum features 130 hold the printhead carriage 76 such that the parallel rows 270 of nozzles 271 ( see fig2 ) extend normal to the paper axis . this provides a relatively simple construction that maintains precise tolerances in the printing gap across all the printhead modules . alignment of the printhead modules in the x direction is less critical as the transverse overlap between adjacent modules is an area where the print from each module is ‘ stitched ’ together under the control of the supervising driver pcb . fig1 and 12 are perspectives of one the printhead modules 42 - 50 . fig1 and 14 show a printhead module installed between its respective ink supply interface 118 and electrical connection unit 120 . the printhead modules are a user replaceable component of the printer and very similar to the printhead modules disclosed in u . s . ser . no . 12 / 339 , 039 filed dec . 19 , 2008 ( our docket rre058us ) the contents of which are incorporated herein by reference . the printhead module shown in rre058us is for an a4 soho ( small office / home office ) printer whereas the printhead module shown in fig1 and 12 has the inlet and outlet sockets 144 and 146 shifted towards the middle of the module for unobstructed ink tube routing to the multiple printhead modules of a pagewidth wide format printer . the printhead modules 42 - 50 have a polymer top moulding 134 on an lcp ( liquid crystal polymer ) moulding 138 which support the printhead ics ( described below ). the top moulding 134 has an inlet socket 144 and an outlet socket 146 in fluid communication with ink feed channels through the lcp moulding 138 . the top moulding 134 also has a grip flange 136 at either end for manipulating the module during installation and removal . the ink inlet and outlet sockets ( 144 and 146 ) each have five ink spouts 142 — one spout for each available ink channel . in this case , the printer has five channels ; cmykk ( cyan , magenta , yellow , black and black ). the ink spouts 142 are arranged in a circle for engagement with the fluid couplings 148 and 150 in the ink interface 118 . fig1 shows the printhead module between the ink interface 118 and the electrical connection unit 120 . the fluid coupling 148 and 150 are in a retracted position where they are disengaged from the ink spouts 142 . ink is fed to the fluid couplings via tube bundles 152 ( only the tube bundle to the input fluid coupling is shown for clarity ). by depressing the fluid coupling actuation lever 154 , both the fluid couplings simultaneously advance to an extended position where they form a sealed fluid connection with each of the ink spouts 142 . the ink interface 118 , the electrical connector 120 and the floor 132 of the datum c - channel 100 create a cradle for each of the printhead modules 42 - 50 . to remove a printhead module , the fluid couplings 148 and 150 are retracted and the user grips the flange 136 to lift it out . fig1 shows the underside of the printhead module 42 between the ink interface 118 and the electrical connection unit 120 . the electrical connection unit 120 provides power and data to the printhead module though a line of sprung electrodes 162 . the electrodes 162 are positioned to resiliently engage contact pads 140 on a flex pcb ( flexible printed circuit board ) 156 secured to the lcp moulding 138 . conductive traces in the flex pcb 156 lead to a series of wire bonds sealed in a bead of encapsulant 158 . the wire bonds connect the flex pcb 156 to the line of eleven printhead ic &# 39 ; s 160 . each printhead ic 160 has a nozzle array with nozzles arranged in parallel rows extending normal to the paper axis ( i . e . the paper feed direction in the print zone ). the lithographic etching and deposition steps to fabricate suitable printhead ic &# 39 ; s 160 are disclosed in u . s . ser . no . 11 / 482 , 953 filed jul . 10 , 2006 , ( our docket mtd001us ) the contents of which are incorporated herein in its entirety . the printhead ics 160 are less than 2 mm wide and each have at least one nozzle row for each color channel . consequently , the wide format printer needs only two staggered rows of printhead modules to provide a pagewidth printhead assembly . this in turn allows the print zone and fixed vacuum platen 26 to have a small surface area . fig1 is an exploded perspective showing the printhead module 46 , electrical connector 120 and ink interface 118 in the broader perspective of the upper paper path assembly 74 . inside each of the electrical connectors 120 is a printhead driver pcb 164 with traces to the line of sprung electrodes 162 . the printhead driver pcb 164 controls the printing operation of the printhead module 46 to which it is connected . all the printhead driver pcbs 164 collectively operate under the overriding control of the supervising driver pcb described in more detail below . fig1 also shows the upper aerosol collector 34 which mounts to the chassis 126 in front of the cover 166 for scanner 18 . the aerosol exhaust fan 168 creates airflow away from the printed surface of the media and vents though the filter 170 . airborne ink particulates are entrained in the airflow and collected in the filter 170 . fig1 to 20 show one of the service modules 22 in detail . the rotating carousel 172 has three separate printhead maintenance stations — a capper 202 , a spittoon / vacuum platen 200 and a microfiber wiping roller 196 . the carousel 172 is mounted for rotation between two sliding mounts 174 . the carousel motor 192 rotates the carousel 172 until the appropriate maintenance station is presented to the printhead . the carousel 172 is lifted and lowered by the lift cams 188 bearing against the sliding mounts 174 which slide within the block guides 176 . the block guides 176 are mounted to the base tray 178 which in turn sits in one of the apertures in the top of the datum c - channel 100 ( see fig8 ). the lift cams 188 are keyed to the cam shaft 190 mount for rotation in the block guides 176 . the cam shaft is driven by the lift motor 194 . the angular rotation of the cam shaft 190 is sensed by a lift cam sensor 186 and the rotation of the carousel 172 is monitored by the carousel sensor 198 . the outputs from these sensors report to the service pcb 204 which coordinates the operation of the lift motor 194 and the carousel motor 192 to provide the various service functions under the over - riding control of the supervisor driver pcb ( see fig3 ). for example , capping requires the carousel motor 192 to rotate the carousel 172 such that the capper 202 presents to the printhead , and then the lift motor 194 to rotate the lift cams 188 to their lifted angular displacement such that the capper extends proud of the vacuum table 88 , through the media path 54 and into contact with the printhead module 42 - 50 . the carousel motor 192 also rotates the wiping roller 196 during a wiping operation to clean away flooded ink and paper dust . microfiber is a suitably absorbent roller material which readily removes ink and contaminants from the printhead ics 160 without damage to the delicate nozzle structures themselves . microfiber also readily releases the ink it accumulates when the wiper roller 196 is drawn across the doctor blade 180 fixed between the block guides 176 . the core of the carousel 172 can also hold a quantity of waste ink . by forming the core from a porous material such as porex ™ and incorporating cavities gives the carousel capacity for ink ejected as ‘ keep wet drops ’ ( i . e . ink drops ejected for the purposes of preventing a nozzle from drying out ) or ink purges ( i . e . high frequency overdrive ejections ) for removing air bubbles , dried ink deposits and so on . the waste ink drains from the carousel 172 through the ink outlet 182 and into the sump feed tube 184 . fig1 is a schematic section view of an alternative carousel 172 . instead of a wiper roller , the carousel 172 wipes the printhead ics 160 a series of soft polymer blades 206 . the operation of the vacuum platen 200 is also illustrated . air is drawn from the central cavity 208 in the carousel core 210 . this generates an air flow from the printing gap 216 , down a series of central bores 212 into the central cavity 208 . make - up air bores 214 connect the central cavity 208 to an intermediate point along the central bore 212 . make - up air passages 218 into the central cavity 208 provide make - air that is entrained into the flow from the printing gap 216 . keep wet drops and aerosols are also entrained into the air flow to the central cavity 208 . fig2 to 23 schematically illustrate the multiple - mode servicing of the printhead assembly . fig2 shows the location of the five service modules 220 - 228 in the fixed vacuum platen 26 relative to the media encoder wheel 24 , the input drive roller 16 and the upper aerosol collection zone 230 . when no media is present in the paper path the service modules can be in a capping mode ( service modules 220 , 222 , 224 and 228 ) or one of the servicing modes ( service module 226 ). the servicing modes are a wiping mode or a spittoon mode . with most of the printhead modules capped , the upper aerosol collection system 34 ( see fig4 ) is deactivated . the supervising driver pcb ( see fig3 ) operates the service modules 220 - 228 individually to provide a greater variety of service protocols for the pagewidth printhead assembly . fig2 shows the printer printing a media sheet 5 that covers the maximum width of the media path 54 . when completely covered , the service modules 220 - 228 are in vacuum platen mode ( see fig1 ). in this mode , the service modules 220 - 228 function as vacuum platens in cooperation with the fixed vacuum platen 26 of the print zone 14 . above the media sheet 5 , the upper aerosol collection system 34 draws ink aerosol away . fig2 shows the printer printing a media sheet 5 that does not cover the maximum width of the media path 54 . the media sheet 5 does not completely cover the service modules 222 and 226 and hence they operate in spittoon mode . the printhead modules 44 and 48 ( see fig3 ) have nozzle arrays that are partially ejecting ink in accordance with the print data , and the remainder of the nozzle arrays are printing keep wet drops to prevent these uncapped , non - printing nozzles from drying out . service module 224 is completely covered by the media sheet 5 and hence operates in the vacuum platen mode . in both the vacuum platen mode and the spittoon mode , air is drawn into the central bores 212 of the vacuum platen 200 as shown in fig1 . the printing operation and the generate aerosols which are removed by the upper aerosol removal system 34 and the airflow into the vacuum platen 200 during spittoon mode . this provides a lower aerosol removal system to complement the operation of the upper aerosol removal system 34 . fig2 and 25 show the vacuum belt assembly 20 . the c - channel chassis 242 supports seven apertured vacuum belts 234 . motor 256 drives pulley 238 via belt 240 . pulley 238 drives the vacuum belt drive shaft 236 which in turn drives the drive rollers 262 for each of the vacuum belts 234 . vacuum belt encoder wheel 258 is mounted to the drive shaft 236 to provide encoder pulses to the supervising driver pcb ( see fig3 ) for generating a nozzle firing clock once the trailing edge of the media sheet has disengaged from the vacuum platen encoder wheel 24 ( see fig3 ). opposite the drive rollers 262 are respective idler rollers 246 . each idler roller 246 is biased away from the drive roller 262 by a spring loaded belt tensioner 260 to maintain correct belt tension . between the drive roller 262 and the idler roller 246 of each vacuum belt 234 is a vacuum belt cavity piece 254 that opens to each side , and to the top section of the apertured belt . between each vacuum belt cavity piece 254 is a plenum section 244 which opens to each side and the bottom ( apart from the two end plenum sections 264 whose outer sides and bottom are closed ). at the bottom opening of plenum sections 244 is a plenum chamber intake 248 for the plenum chamber 252 . three vacuum blowers 250 are mounted under the c - channel chassis 242 . openings ( not shown ) in the top on the c - channel 242 allow the vacuum blowers 250 to draw a vacuum in the plenum chamber 252 . the low pressure in the plenum chamber 252 reduces the air pressure in the plenum sections 244 as well as the vacuum belt cavity pieces 254 . air is drawn through the top section of each vacuum belt 234 . when covered by the media sheet , the pressure difference between the interior cavity pieces and atmosphere apply a normal force to the sheet . the vacuum drawn in the plenum chamber is set such that the media sheet can slip relative to the vacuum belts 234 while the media sheet 5 is in the nip of the input drive roller 16 ( see fig2 ). when the trailing edge of the media disengages the input roller , the feed speed matches the vacuum belt speed . at this stage , the nozzle firing pulses are timed using the vacuum drive shaft encoder wheel 258 . this avoids artifacts in the print at the trailing section of the media sheet . fig2 is a rear partial - perspective of components from the ink distribution system . the large ink reservoirs 266 are gravity fed by bottles 60 ( see fig7 ). in turn , the accumulator reservoirs 70 are gravity fed by respective ink reservoirs 266 . each accumulator reservoir 70 feeds all printhead modules 42 - 50 ( see fig2 ) with a single channel of ink . as shown in fig2 , the printhead modules arrange the nozzles 271 in columnar groups 270 . each of the parallel columnar nozzle groups 270 correspond to one of the ink containers respectively and one of the accumulator reservoirs 70 respectively . a return line ( described later ) returns to the accumulator 70 via peristaltic pump 268 . each of the printhead modules 42 - 50 have a bypass line between the feed line and the return line via a respective pinch valve assembly 86 ( described in more detail below ). fig2 depicts a small part of the fluid circuit to the printhead modules with valve , sensor and pump omitted . it will be appreciated that the ink delivery system is sophisticated and versatile but requires a systematic tube routing arrangement for ease of maintenance , testing and production . the structural cross member 316 extends between the left and right side plates 96 , 98 ( see fig8 ) of the lower paper path assembly 78 . the ink reservoirs 266 are mounted at a higher elevation than the accumulator reservoirs 70 , which hang beneath the cross member 316 for gravity feed via the tubes 294 . the tubing cover 318 forms a cavity with the cross member 316 to retain the tubing . the accumulator reservoirs 70 are also mounted such that they are at a lower elevation relative to the nozzles 271 . in the system described , the ink level in the accumulator reservoirs 70 is maintained about 65 mm to 85 mm below the nozzles 271 . this generates a negative hydrostatic pressure in the ink at the nozzles 271 so that an ink meniscus does not bulge outwards which would be prone to leakage through wicking contact with paper dust or similar . the sequential priming , de - priming and bubble purges of the printhead modules will now be described with reference to the diagrams shown in fig2 to 33 . these diagrams relate to a single ink channel ( i . e . color ) and show only printhead module 42 . the accumulator reservoir 70 has a float valve 284 that maintains the fluid level 280 within a small range . the float actuator 286 for the float valve 284 is configured to maintain the fluid level 280 about 65 mm to 85 mm below the nozzle elevation 292 . an inclined filter 288 in the accumulator reservoir 70 covers the outlet 320 to the feed line 272 . the feed line 272 has a feed branch line 302 to the printhead module 42 . other feed branch lines 296 extend to the remaining printhead modules 44 to 50 ( not shown ). a feed line valve 298 is in the feed branch line 302 for selectively closing fluid communication between the printhead 42 and the feed line 272 . a return line 274 leads from the return branch lines 304 , 414 from the printheads to a peristaltic pump 268 used to prime and de - prime the printheads and to remove bubbles from the system . the feed line 272 also leads to a bypass line 276 which connects the feed line to the return line via a bypass valve 278 . the pump 268 is between two sets of check valves 324 and 326 , each with an outflow pump filter 306 . this ensures that particulate contaminants from spalling in the pump 268 do not reach the printheads regardless of which direction the pump operating while also allowing the pump to force ink flow through only one filter at any time . safety pressure relief valves 308 ensure that the check valves 324 and 326 are not compromised . the return line 274 joins the accumulator reservoir at a return line inlet 322 which is positioned about 45 mm to 55 mm above the ink level 280 . this allows the pump 268 to generate a hydrostatic pressure difference between the feed line 272 and the return line 274 when the bypass valve 278 is closed . the return line 274 has a manual three - way valve 310 that can direct flow to a sump instead of the pump 268 . this allows manual rectification of ink cross contamination . similarly , the accumulator feed tube 294 also has a manual three - way valve 312 to divert flow to a sump in the event of gross color cross contamination . the head space in the accumulator reservoir 70 is vented to atmosphere through valve 290 . this valve incorporates a filter to keep airborne particulates from the ink in the accumulator reservoir 70 . initially , the bypass valve 278 is open , the feed line valves 298 and the return line valves 300 for each printhead are closed and the pump 268 primes the feed line 272 , the bypass line 276 ( see fig2 ) and the return line 274 including the filters 306 , the check valve sets 324 and 326 , and the pump 268 itself ( see fig3 ). the printheads 42 to 50 are then primed sequentially . referring to fig3 , the bypass valve 278 is closed and the feed line valve 298 and the return line valve 300 for printhead 42 are opened . the pump 268 pumps forwards ( pump rotates clockwise as shown in the figures ) and ink is drawn through the feed branch line 302 into the printhead 42 . a slug of displaced air is drawn into the return line 274 . as shown in fig3 , the pump 268 continues until the air is purged from the return line 274 . the feed line valve 298 and the return line valve 300 are closed again and the process is repeated for the next printhead to be primed . once all the printheads have been primed , the pump 268 does not operate during printing . fig2 shows fluid flows during a print job ink supply to the printheads 42 - 50 is generated by capillary pressure to refill the nozzles . the capillary action drives the ink refill flowrate by the negative hydrostatic pressure generated by the elevation difference with the accumulator ink level 280 acts to reduce this . in light of this , setting the elevation difference in a workable range that avoids cross contamination at the nozzles but doesn &# 39 ; t hinder refill flow rate , is the most practical solution . fig3 shows the de - prime protocol . the bypass valve 278 is opened and the feed line valves 298 and the return line valves 300 for all the printheads 42 - 50 are closed . the pump 268 is run in reverse and air is drawn through the return line 274 , the bypass line 276 and the feed line 272 . next it is a simple matter to open the feed line valve 298 and the return line valve 300 for the faulty printhead , close the bypass valve 278 and run the pump 268 in reverse some more to deprime the printhead . once replaced , the priming protocol is run for each of the printheads 42 - 50 to ensure stray bubbles in the branch lines are purged . fig3 to 36 show one of the pinch valve assemblies 86 of the type used widely throughout the ink distribution system . the dc motor 328 drives the cam shaft 330 mounted between the end cap 344 and the side plate 346 . the cam shaft 330 extends through the spring plate 334 such that the cam 332 engages the bottom of the spring plate 334 when rotated . the valve base 340 defines five tube openings 348 for the tubes 10 . when the cam 332 engages the spring plate 334 at its minimum radius , the tubes 10 are not compressed or negligibly compressed , and the pinch valve is open . when the cam rotates such that it engages the bottom of the spring plate 334 with it maximum radius , the spring plate presses down on the tubes 10 ( with the assistance of the springs 336 compressed against the cover 338 ) to pinch the tubes shut . the pinch valves are not the most reliable of valves and a small amount of leakage is not uncommon . however , the pinch valve assemblies 86 have a particularly basic design which reduces their unit cost . this is of great benefit to the wide format printer described herein which uses a multitude of valves throughout the ink distribution system . furthermore , a completely leak free valve seal is not necessary for the various ink flow control operations . a flow constriction will suffice for raising the upstream pressure in order prime ( or de - prime ) particular areas of the printer . hence the shortcomings of the simple and inexpensive pinch valve assemblies 86 are irrelevant to the wide format printer 1 ( see fig1 ) described here . the accumulator reservoirs 70 are also inexpensive relative to the complexity of their operation . fig3 and 38 show the separate components of an accumulator reservoir 70 . the tank 356 holds the float 286 and the float valve 360 . glass beads 362 may be added to increase the weight / decrease the buoyancy of the float 286 . the float is sealed shut with a lid 352 and a floor 342 . a pair of lever arms 354 engage a corresponding pair of hinge points 366 within the tank 356 so that the float 286 can angularly displace within the tank 356 . the tank lid 350 seals to open top of the tank 356 , but the interior is still vented to atmosphere by the vent valves 290 . the inlet manifold 358 seals to the bottom of the tank 356 . the outlet is a simple tube 320 which is covered by a one micron filter 288 . the valve rod 360 hooks onto the float 286 proximate its free end . at the bottom of the valve rod 360 is an umbrella check valve 364 that seals against an opening in the bottom of the tank 356 . when the ink level in the tank 356 drops , the float 286 lowers and the weight of the ballast marbles 362 force the valve rod 360 to unseal the umbrella valve 364 from the opening . this allows the ink in the inlet manifold 358 , under pressure from the ink gravity feed , to flow through the opening into the tank 356 . this raises the ink level and hence the float 286 so that the valve rod 360 again lifts the umbrella valve 364 to seal shut the opening in the tank 356 . fig3 is a cable diagram of the electrical control systems . all the electrical , electronic and micro - electronic components are directly or indirectly under the control of the supervisor driver pcb 400 . different sub - assemblies may have their components operated by their own pcbs such as the ink distribution pumping sub - system pcb 370 , or even the printhead module pcbs 372 - 380 , but this operation is coordinated through the over - riding control of the supervising driver pcb 400 . other electrically actuated components such as the pinch valve assemblies 384 and the vacuum blowers 382 are directly controlled by the supervising driver pcb 400 .