Ink Choke and Ink Systems
The OP is having trouble with a Roland VS series printer. The Ink Choke is only found in machines that are VS or newer.
I cannot cover the exact process of damper replacement in a VS unit in this forum, but I think that it will help if I offer some background on ink choke and the differences between the old type and new type ink system.
Ink choke is something that is found on RA/VS units (and newer)... essentially any Roland printer with a DX5 or newer head.
Depending on the model, it's either a manually operated bar (VS/RA) or electrically operated valve (VSi/RF/XF/XR) that closes/crimps the ink lines. The ink choke mechanism is found behind the ink cartridge bay.
The manual value is actuated from the left side of the printer using a 5mm Allen (VS/RA), and the electrically operated valve is operated via the Service Menu (VSi and above). Note: Keeping ink lines crimped for a long period of time can damage the ink lines and cause inkflow issues.
Self-servicers not familiar with the ink system on the VS/VSi series should be cautious before digging into ink system maintenance. There's a lot more going on under the hood as far as the ink system goes than previous models. Servicing these machines is not brain surgery, but you can get yourself into trouble ($$) if you don't understand the systems before digging in. Always call your trusted service tech for help before you cause more damage. Many techs are happy to teach you what they know.
Legacy DX4 based models (SP, VP, Soljet Pro II/III, etc) had a very simple ink system. A sharp needle punctures the cartridge septum, and the ink line carries the ink to the small dampers which sit on the printhead manifold. (Dampers allow air to be removed, filter the ink and prevent backflow to the cartridge)
These systems are gravity fed, and a negative pressure in the ink cartridge draws the ink back when you have an air leak or if you remove the damper from the ink line. (The ink needles are just slightly lower than captop height). Individual captops make it easy to clear individual heads and reload individual ink lines during maintenance.
While these are nice simple systems to maintain, the shared captop systems (aka SP series) do risk wicking from one channel to another when cartridge pressures are uneven (i.e. magenta wicks into the yellow line). Also, because of the inkflow limitations, these machines are also prone to ink starvation when running fast with heavy coverage.
The newer DX5+ machines changed the mechanics of ink system-- just slightly, but enough to add a little complexity.
First, all of the VS/VSi units have recirculation systems for white/metallic inks. If you don't use white/metallic ink, the lines in the re-circ system are filled with regular process ink. So you still have additional pumps and Y-joins to factor in...even with the regular inks.
While the new machines are also gravity fed, you get some forward pressure as the inks are higher than the captop. To deal with this, Roland added an ink choke, to clamp the inklines during service. (Choke is also used during Choke Cleaning, but that is a different topic). Remove a damper without clamping the ink choke and you may have a surprise mess on your hands. Clamping allows you to replace individual dampers without having to reload all of the ink in the system. With the circulation system--and depending on the ink color and which channel it uses-- loading an inkline may not be as simple as drawing ink through the newer style damper.
Again, this isn't rocket science, but a little misstep and you can fry your head ($2,200-ish) or be fighting inkflow, air bubbles, drop out... and be wasting a ton of ink trying to work it out because you have a single captop.
At the end of the day, consider a trusted experienced tech to help-- if you have one.
~E
