Which ink does the Epson WorkForce Pro WF-7840 use?

The Epson WorkForce Pro WF-7840 uses the Epson 812 family: separate black, cyan, magenta and yellow cartridges, each available as a standard 812 or a high-yield 812XL.

The XL gap on this printer is wide enough that standard cartridges are hard to justify. The 812XL black is rated at 1,100 pages for $47.99, which is 4.36c per page, against 6.85c for the standard 812 black at 350 pages for $23.99. Each XL color is also rated at 1,100 pages, at $36.99, near 3.36c per page, where the standard colors sit at 5.33c. Buying standard 812 cartridges adds about 57 percent to what every black page costs you.

Compatible and remanufactured 812 cartridges fit the WF-7840, and on a printer that holds this much ink the savings are worth having. Epson does run a firmware restriction here, though. Its own guide for the model says non-Epson cartridges that worked before an update may not continue to work after one, so hold automatic updates while you are buying compatibles. You will probably see a non-genuine cartridge notice, which is a warning rather than a refusal to print. Buy from a seller that keeps its chips current and you are unlikely to have trouble.

The head on this model is fixed and stays in the printer, which means clogs rather than cartridge failures are the thing to watch. Banding, a missing color or a wrong color cast almost always points at nozzles, not ink level, so print a nozzle check pattern and read it before you replace a cartridge. Run one cleaning cycle, then a second only if the pattern got better. If two do not clear it, leave the printer switched on and idle overnight so the ink softens rather than running cleaning again, because every cycle flushes ink into the maintenance box. That box is its own consumable on this model, and once it fills the printer will refuse to print or clean until you fit a new one.

Order matters on a machine that holds this much ink. Set the printer software's automatic update check to Never before the compatible cartridges arrive rather than after, because Epson's guides document how to install firmware and say nothing about reversing one. Keep a genuine cartridge in the drawer as a test piece rather than as a spare. If the printer stops accepting a compatible, a genuine one that prints normally tells you the refusal came from the firmware and not from the contacts, and that is worth establishing before you order another set.