Canon and CISS - why everyone has issue with air?

I have iP7250 + CISS + dampers and i printed on it 25000 double sided A4 sheets (so it is 50000 one sided)

Of course i also have an issue with air getting into cartridges. I read on this forum that Canon + CISS always means air issue.

But in my case it is strange. Currently I have mainly problems with Yellow and Magenta cartridges. I have to remove air from them every a few books printed. The other three cartridges works very good.

But I don't understand how the air gets to these cartridges. I think there are three possibilities:
1. The CISS is not tight. But this depends on the quality of CISS and therefore is fixable.
2. The air gets from space between printhead and cartridges. Most forum users thinks that way.
3. The air pass through printhead to the cartridges (for example during cleaning)

The question is if we assume that point 1 is not a problem, which from 2 and 3 makes issue and if it is possible to fix it? For example using some in-cartridge damper or glueing cartridges to the printhead?

What do you think?

The rubber "gasket" between the print head inlet and cart outlet is not a very good air seal. It's primary purpose is to prevent the ink at the cart outlet from drying and blocking the flow. You might try increasing the contact pressure between the cart outlet and gasket by adding a thin sheet of custom cut silicone (or equal), although use of that sheet may, in itself, cause an air leak unless close attention is paid to fit-up.

Typically, air enters the print head nozzles backwards from ink flow if the flow rate from the cart is insufficient to supply the nozzle's demand. This is caused by carts that deliver insufficient flow, such as via a plugged air vent...

Canon print heads operate with VERY low head pressure (say 1" of water, if not much less). If you cannot provide enough "supply pressure", there is no ink flow. A slight vacuum at the print head inlet is MORE than enough to disturb flow.

During cleaning, a very slight vacuum is applied to the nozzle outlets via the purging system to encourage flow. Air should not enter the nozzles during cleaning if the purge system is operating correctly.

Except most if not ALL CISS units for CANONs already come with little donut shaped silicone seals meant to supposedly "Solve" that lack of sealing problem.

The air leaks come from the constant reciprocating lateral forces from the ink line ribbon as the head traverses back and forth. Flap Flap Flap Flap! You get the picture.

Unlike Epson carts which are securely Locked in place on the carrige, and have print head's ink stem actually penetrating and sealing the exit ports for the carts, small to medium format consumer Canon printer Cartridges only seal against the print head ports by contact only!

Which makes it a BAD choice or design for a CISS.
If only people would accept that!
Not saying that a CISS will NEVER work on a CANON. Just saying that they are not as reliable as those designed for Epson printers.
Joe

Did you realize that the newer Epson Photo oriented AIO are also contact based cartridges as well. XP600 and up series including the XP800 etc.. Yikes...

I can tell you that I had forgotten to replace the rubber seals on the Canon printhead one time and the printer still worked. So I imagine it actually may not be a seal problem. However...air is still the culprit. The ink migrates down the printhead purely from surface tension and the ink link between the outlet pad and inlet screen is where the source of the problem begins. Once the link breaks, there is a chance of air trapped in the column of ink. This column of bubble infused ink then causes the banding. That is the reason why Canon initiates a head clean each time the cover is opened because they are thinking that the only reason the cover is opened is when the cartridge is changed and this could possibly trap air in the ink channel when a cart is removed and replaced.

The carts flapping back and forth might cause a small pumping action on the outlet porous pad and create small bubbles or foam and this then goes down to the printhead thus causing banding.

The lateral motion of the print head actually produces significant pressure pulsations in the supply tubing of a CISS during the high accelerations at end of travel. Or even at high "Jerks" (the third derivative of position) which must happen during print heard reversals.

Thank you for your answers.

Could you tell me if all old Canon printers are also bad for CISS? Even these from before 2000?

If the "Connection" between Cart and Print head is based on just simple contact like in today's Canon Home ( Not Pro printers with external ink tanks and ink lines ) then the answer is yes.

Joe

Are Canon Pro printers reliable when used with CISS?

No!
Joe

But they don't have simple contact connection as you said