that's the classic negative pressure readout found on most every chinese printer with secondary tanks.
your printer is gravity feed where by comparison this device is for a printer that purposefully loads the lines with too much positive/gravity then with a tiny amount of adjustable vacuum pulls back on that ink line in order to balance the flow to the heads. if you turn this down on such a printer, the heads will start dripping.
what you need to do is diagnose the ink supply issue. it could be a number of things starving your black channel under a heavy load. i'll start with the quickest/easiest to check first.
1- change the damper to the black lines. they may be clogged.
2- you might not have full positive pressure at that line. pull a vacuum from the waste line to make sure that the black channel isn't vapor locking.
3- clogged lines. black has a lot of sediment and at the low spots in the ink train, there can be deposits. cleaning the lines consists of blasting solvent backwards through the
printer into empty cartridges. also a piece of
paper from a cart can clog the piercing needle. backwards flush will knock this out. (this may be your issue)
4- bad batch of ink. if the ink viscosity is off, it will starve the head. epson heads need very low viscosity.
5- bad cartridge. some ink carts collapse incorrectly and cause the cart to pull a vacuum as they feed ink.
6- kink in the black line.
7- clogged print head manifold filter. each head has a screen in it. this can clog and starve ink. a damper swap is an easy to see if black will more willingly flow at a different port on your manifold.
