General question on Designjet ink tubes

[theengel]

I haven't been servicing the plotters for very long. Usually, if there's air in the tubes, I've been assuming that the cusomer needs inktubes... because air should get into the tubes. But am I wrong on this? Should I try using a syringe to suck all the air out before buying expensive inktubes?

[walterman]

Have you tried to purge the air out? I as well have not serviced a ton of the designjets, however, I always see "air" in the tubes. I'm almost certain that if you try to purge the lines and you don't see the ink move is when you have a leak in the line because it will not pressurize and they may need to be replaced at that time, factoring out all other variables that may cause such an issue.

[walterman]

Oh, I got a little ahead of myself, I forgot to ask you.. Are they experiencing any issues or was this just an observation? Because, if this is just an observation, it is quite normal to have "air" in the lines.

[Kiran Otter]

Air in the tubes is a common issue with older machines. The seals at the carriage (where the printheads go in) dry rot and allow air to be sucked into the tube when the printer sits idle. Then when you print, and the printer either pumps (500, 800, Z&T series, etc with 69/130ml ink cartridges) or pressurizes (1050C, 5000/5500) the ink, this pushes the air into the printhead, often causing it to run dry which ruins the nozzles that spit the ink onto the paper, namely because it uses heat (see Inkjet printing - Wikipedia, the free encyclopedia) and the ink acts as a coolant.

I've experimented many times with trying to vent the air out of the tubes, but this isn't a 'fix'; the seals are still shot and air will just re-enter the tubes again. Plus, even with the air out of the tubes, there's no way to get ink back into the printhead, other than using some kind of tool which I've seen on ebay for refilling printheads. It's a closed system; the printhead comes with ink in it, and there's no air allowed into the system at any point. Even the primer just pushes on a tiny diaphragm inside the printhead to increase the ink pressure and make the nozzles spit a little to get stubborn nozzles going again. (This is on the 1050C/5x00; the T&Z series use suction through the service station to prime.)

So this is usually what happens: Printer gets air in one or more tubes, and those printheads begin to fail, and the printer reports through the front panel to replace one or more printheads. Customer does so, and the printer works great again. But only because the new printhead has ink in it to begin with (about 7ml, I think.) Once these new printhead(s) run dry, the printer again tells them to replace the print head, so they spend another $$$$ on more printhead(s).. and the process just repeats. And each time, the dried heads are essentially trash.

Until you replace the tubes, the problem will happen again and again. It happens much less on printers that are in constant service, but especially with the 5x00 series.. if the printer sits for a month or more between uses, expect air in the tubes eventually.

You can also get air in the tubes from using refillable ink cartridges. Especially on the 130ml inks that go in the T&Z series. There's refillable cartridges that don't use the bongo pump to pump the ink, they just rely on gravity, and since the chip on the cartridge is faked, the printer will never know the true ink level. So if the cartridge runs dry, it will begin to suck air into the tube.

LPS Computer re-manufactures tube assemblies and puts better seals in them; I've been using them exclusively instead of original HP tube assemblies, because they're not only cheaper, but come with a 1 year warranty and with the better seals, should outlast the HP tubes.. and probably the printer. Even given this, I did just have my first failure of one of their tube assemblies, 16 months after it was installed, but they honored the warranty and are replacing the tube assembly.

And like I said, I've tried using a syringe and letting the air out of the tubes. All it does is make an incredible mess, and you're still left with a dry printhead. Think of sticking a straw into a bottle, and sealing the top around the straw. You can put some liquid through the straw into the bottle, but eventually the air pressure will prevent any more liquid entering because of the seal. There's no way for the air to escape. And this is especially true if you've replaced the tube assembly. So customers are often faced with buying one ore more new printheads even after you've replaced the tubes. Mine with the failed LPS tubes had to get 3 printheads. (Luckily found them on ebay for $115 for all 3.)

Sorry if I've been a bit long-winded, but this has been probably the biggest problem with HP Designjets I've had. Only superseded by user's lack of knowledge on how to use the printer correctly.

Kiran

[Kiran Otter]

.... it is quite normal to have "air" in the lines.

In a perfect world you shouldn't see any air, but a tiny little gap in the tube where there's a air bubble is OK. If you see entire sections of tube that are clearly empty.. that's bad.

Kiran

[Kiran Otter]

I just realized I linked to the wrong Wiki article. HP uses thermal inkjet technology, not piezoelectric; it's what I get for not being awake.

Inkjet printing - Wikipedia, the free encyclopedia

Kiran

[theengel]

Thanks for the long-winded explanation. It clears up a lot for me. I was only asking this as a general question, because I'm seeing it a lot. I especially see it when I tell the customer, "you need X part, for $300." The customer will 'think about it.' A month later, they want it NOW--and the machine has been sitting idle all that time. Guess what--a few bad printheads and air in the lines.

And now that you're saying all this, one particular call makes sense to me. They replaced the cyan printhead, but I told them they need new inktubes. Over a month later, (they were using it the whole time) they gave me the go-ahead. But now their cyan won't work. I had told them they need another printhead, but I've been second-guessing myself since then (two days ago). I'll find out Monday if the new printhead works.

Yeah--I've been using LPS too.

Thanks again.

[walterman]

I went to LPS Computer web site and they had a very informative tutorial entitled " HP Designjet 1050, 1055cm ink tube replacement." It may clear up some of your questions as well.