Pro24F yellow starvation - but not.

[IvanDD]

Our yellow now dies out over the course of a print. When I purge the heads with the valves open, I get a steady stream of yellow.

I thought maybe there was some sort of starvation going on but the tanks above the head for yellow seems to be filled fine, since I can drain if I need to. When I do that, I hear the pump kick in the refill the tank. So it sounds like the pump and the tank aren’t the issue.

On the second picture. I paused the print when it started fading. Let it sit for 5 min, and when I resumed it was back to normal. That absolutely sounds like a starvation issue. However after the print finished and the yellow was very faded, I immediately opened the head valve and did a purge and ton of yellow came pouring out of the nozzle. That does not sound like a starvation issue.

I turned the back pressure way down to see if that helped, it did not.

Im stumped.

 

[Jhake]

I’ve run into this exact yellow fade plenty of times and it almost always shows up more once the weather turns cold and dry. Based on what you described (yellow fading during a long print, coming back after a pause, but purging strong), it’s not a full blockage; it’s a flow consistency issue that’s being magnified by temperature, humidity, and the nature of yellow ink itself.

Here’s the breakdown:

• Yellow is chemically more sensitive – Yellow pigments are usually organic and have larger, less stable particles. They settle faster and thicken more when things cool off. When your shop drops below ~68°F, the ink’s viscosity goes up, which makes it harder for that channel to maintain flow. Even small restrictions in the damper or manifold show up immediately as fading.
• Cold and dry air makes it worse – When the humidity drops below about 35%, static and microbubbles become a real problem. Tiny air pockets can form in the yellow line, compress during printing, then rebound when you pause; which perfectly matches what you’re seeing. You get the fade, you pause, pressure equalizes, and yellow comes back strong.
• Back pressure & temperature…Turning down the back pressure in these conditions usually hurts more than it helps. The thicker the ink, the more pressure it needs to stay consistent. Bringing it back to spec (or slightly higher) and keeping the ink and print room around 70°F at ~45–50% humidity usually stabilizes things.
• Why yellow looks so much worse. Even if all inks lose a little density when flow drops, yellow has the lowest optical density of the CMYK set; so a 10% drop in flow looks like a 50% color fade. It’s not that the head is “worse,” it’s just more visible with yellow

So, the science behind it checks out: colder temps thicken the ink, dry air adds static and micro-bubbles, and yellow’s chemistry plus optical sensitivity make it the first one to show it.

If you’ve already confirmed the pump and tank are working fine, I’d check the yellow damper and bleed the line for air. Then warm the room up a bit and bring humidity up if possible; you’ll probably see the channel stabilize.

 

[IvanDD]

I’ve run into this exact yellow fade plenty of times and it almost always shows up more once the weather turns cold and dry. Based on what you described (yellow fading during a long print, coming back after a pause, but purging strong), it’s not a full blockage; it’s a flow consistency issue that’s being magnified by temperature, humidity, and the nature of yellow ink itself.

Here’s the breakdown:

• Yellow is chemically more sensitive – Yellow pigments are usually organic and have larger, less stable particles. They settle faster and thicken more when things cool off. When your shop drops below ~68°F, the ink’s viscosity goes up, which makes it harder for that channel to maintain flow. Even small restrictions in the damper or manifold show up immediately as fading.
• Cold and dry air makes it worse – When the humidity drops below about 35%, static and microbubbles become a real problem. Tiny air pockets can form in the yellow line, compress during printing, then rebound when you pause; which perfectly matches what you’re seeing. You get the fade, you pause, pressure equalizes, and yellow comes back strong.
• Back pressure & temperature…Turning down the back pressure in these conditions usually hurts more than it helps. The thicker the ink, the more pressure it needs to stay consistent. Bringing it back to spec (or slightly higher) and keeping the ink and print room around 70°F at ~45–50% humidity usually stabilizes things.
• Why yellow looks so much worse. Even if all inks lose a little density when flow drops, yellow has the lowest optical density of the CMYK set; so a 10% drop in flow looks like a 50% color fade. It’s not that the head is “worse,” it’s just more visible with yellow

So, the science behind it checks out: colder temps thicken the ink, dry air adds static and micro-bubbles, and yellow’s chemistry plus optical sensitivity make it the first one to show it.

If you’ve already confirmed the pump and tank are working fine, I’d check the yellow damper and bleed the line for air. Then warm the room up a bit and bring humidity up if possible; you’ll probably see the channel stabilize.

I will admit there have been cooler temps recently but we're still in Florida, and this hasnt happened in the 5 years I've been here. The reason we noticed it was we were printing some red full sheets and it turned magenta by the end.

I get absolutely everything you're saying, and we do not have a humidifier. so its entirely possible. The part I dont get is that even when the yellow is starved, I can still drain the yellow tank via the valve at full force. I'm not seeing any starvation from the tank, and the tank seems full.

Thank you for your reply.

 

[Superior_Adam]

I had this issue and the yellow ink had hardened inside the sub tank above the heads. Replaced the tank and no more issues. It was reducing the amount of ink inside the tank.