How I refurbish inkjet printers - some details
by Steve Greenfield aka Alien Steve
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More information about the problems I think are occurring with bulk ink systems and how I attempt to solve them in my Hyrdraulic Constant Pressure CIS tanks and cartridges.

Previously posted on the Epson_Printers list:

From my tests and what I've read about other's problems with bulk ink systems, I think there is a mostly unrecognized problem with ink level in the bottles. At least a couple of CIS sites specifically say they won't make them for the 1520 due to this problem. I ran a 1520 for quite a while, I just kept moving the bottles up as they ran out and could easily print 50 or 100 sheets without a cleaning cycle. Now I have designed and build a constant pressure CIS system.

From reports and my tests with a 1280, I think the 1280 also tends to be sensitive to ink height. Most Epsons are probably at least somewhat sensitive to it.

Ink too high: extra ink is forced into the head, first print after not printing for some period of time bands, it may involve random droplets of ink or if you look at the park pad it may be unusually wet. A cleaning or two fixes it right up.

Ink too low: ink is siphoned back out of the heads, sucking air up into the nozzles. Banding, a few head cleanings and it is OK. Severe cases, or if no printing for quite a while, may require sucking foamy ink out of the cartridge on occassion.

The important thing is the level of the top of the ink in the bottle. The sweet spot seems to be between the height of the bottom of the head and the bottom of the cartridge. On a 1280 that is the height of the line across the front between the top and bottom halves of the case.

Then I received this response:

 --- <****> wrote:
Steve; You're right-on on the 1280 1520 bulk systems. We had a couple brands of 1520 systems, built another ourselves and as time passed switched over to the 1280s and a bulk systems from Niagra II, MIS, and Tropical Graphics. They all ran fine for a time but at some point each one would develop an ink starvation problem that could be tweaked by adjusting the height of the ink but rarely could you get it to last long.

There were times we could print 40-50 pages without a cleaning cycle and other times when we would have to clean every 5 or 6 sheets. The big problems is that we never knew when a problem would occur and so all the print jobs had to be baby-sat.

I also think that the 1280s and 1520s have a dificulty sucking the pigment inks. We ran dye inks thourgh one 1280 system (for office paperwork not transfers) without a flaw forever. One bulk manufactirer even told us that they would no longer make a bulk system for the 1520 because they could not get enough suction out of those printers to draw the ink. We also noticed that using the same bulk ink system and moving it from one printer to another did not always have the same result. We had one 1280 that consistently had trouble drawing yellow ink, another magenta, no matter what bulk system they were hooked to.

I tend to think that the 1280s and 1520 are just on the edge of having the capability to run the pigment bulk systems and so we constantly face tweaking.

(used with permission)

And my response to that:

What is peculiar is that the 800, 1520, and 3000 all use exactly the same head. Not enough people using the 800 with a bulk ink system to make any judgements (is anyone still using an 800?). The 3000 has those bagged tanks. I think they provide somewhat of a regulatory effect on ink level.

My hydraulic constant pressure ink tanks hold the ink pressure to within about 1/16th of an inch.

Many people don't realize that you also need an air bubble inside the cartridge. Yes, you need an air bubble. The air bubble acts as sort of a spring to buffer ink flow from the bottles. Without it, when printing starts it is pulling on the entire column of ink from the head back to the top of the bottle. Then when a nozzle stops drawing ink, inertia keeps the ink going. Maybe you've heard this in the past in old houses, it's called Water Hammer when the pipes make a Bang as you shut off a faucet quickly. All houses now include a (wait for it) dead end pipe with an air bubble in it.

With the air bubble in the top of the cartidge, as the print head pulls out ink the air bubble grows a little larger as it drops barely below ambient air pressure. This creates a slight suction that pulls ink in from the bottles. If the nozzle does a lot of heavy printing and gets some ink flowing, then stops suddenly, instead of a column of ink 20 inches long slamming ink out the nozzle, it simply compresses the air bubble a little and this then springs the ink back slightly into the bottle until everything is again at ambient pressure.

Note that flexible sidewalls can substitute for this air bubble, for instance the C8x and C6x series of Epsons have a thin plastic "sticker" that seals one side of the cartridge and this can flex in and out in place of an air bubble.

It might seem strange that a column of ink 20 inches long "slams" into the nozzles but gently compresses an air bubble. The difference is volume. 64 nozzles smaller than a human hair versus a bubble that may be 20 times the diameter of the hose. Turn on your shopvac. Put a funnel over it, small side out. You get a jet of fast moving air. Now put a large funnel over it (or make one out of cardboard) that expands the size. Slow moving air.

Or try this for another illustration: hook up a blunt needle to a 30cc syringe. Fill the syringe with water, knock all the air out and squirt it out just like every doctor on TV does. Now stick it back into the water and pull 30cc of water into it. It's hard! You are pulling every cc of the way.

Now empty it out (notice how hard you must push to empty it), and suck 5cc of air into it. Stick it back in the water and fill it. It's much easier! You can pull it immediately up to 10 or 15cc, hold it, and just wait for it to fill. Empty it and notice how much easier it is to push, as you can push a bit then hold it as air pressure continues to push the water out. You can pull, stop, pull the plunger again and again and the net effect with an air bubble is that you can move it easily but the water will continue to fill the syringe as if you were just steadily pulling the average of all those starts and stops.

BTW, this problem can appear to be ink starvation. Without the air bubble: As a color starts printing, the sides of the cartridge pull in a little, then if heavy printing continues it may starve the nozzle a little as inertia is overcome and then ink flows and it prints all nozzles; then that color stops or slows but ink keeps flowing, initially the sides of the cartridge may expand slightly, then it may force a little ink out. But the droplet blocks a few nozzles, making it look like some nozzles are blocked internally. As the print head whizzes (or wizzes) along, the drop may dislodge causing a random droplet which may spray off the edge or just on the edge of the paper, and the nozzles stop banding.

Some people say I think too much about things. I say there aren't enough hours in the day, I want to learn more and figure more things out. When I was an electronics tech, after my work was done I'd work on the tough dogs that other techs had given up on.

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Alien Steve