Why Canon Spongeless Refillable Cartridges Don't Leak: Understanding Pressure, Airflow, and BCH Replacement Covers for PG-240, CL-241, PG-245, and CL-246

Question

I am interested in the Canon spongeless refillable cartridge modification for cartridges such as the PG-240, CL-241, PG-245, and CL-246, but I need to understand how it actually works before buying.

If pressure is added to the cartridge, why does that pressure not keep forcing ink out of the printhead? On the other hand, if there is no pressure inside the cartridge and it is only at normal atmospheric pressure, why would the ink not eventually leak out over time? Also, if a vacuum forms inside the cartridge, wouldn't that stop the ink from flowing?

With a normal Canon starter cartridge, if too much ink is added and the sponge cannot hold it, ink leaks from the printhead. If the sponge is removed in a spongeless modification, why would the cartridge not behave the same way and leak?

I also tested an old Canon CL-561 cartridge by removing the cover, pouring distilled water into the three chambers, and leaving it overnight. The water leaked out. Why would ink not leak in the same way after using the spongeless cartridge modification?

Answer

The key point is this: a spongeless cartridge is not just an empty tank with ink poured into it. If you simply remove the Canon cartridge cover, remove or bypass the sponge system, pour liquid into the chambers, and leave the cartridge open or improperly sealed, it will leak. Your distilled water test on the Canon CL-561 is a good demonstration of that. Without the correct top cover, air path, pressure regulation, and sealing structure, gravity and uncontrolled airflow will allow liquid to escape through the printhead.

That is why the BCH replacement cover is not just a lid. It is a functional pressure-regulating component.

If you look closely at the BCH replacement cover, you will notice a small white column next to each refill hole. That part is the pressure regulator. It is one of the most important pieces of the design. Without that BCH cover and its pressure-control structure, the cartridge will not behave correctly. In other words, the spongeless system depends on both the modified cartridge body and the replacement cover working together.

A standard Canon cartridge uses sponge material to control ink movement. The sponge holds ink by capillary action, much like a paper towel holds water. The sponge prevents all the ink from freely rushing toward the printhead, and it also helps maintain the correct balance between ink supply and air replacement. When the printhead fires, it draws a tiny amount of ink, and air slowly replaces the used volume so the cartridge does not form too much vacuum.

When you overfill a regular Canon starter cartridge, the sponge becomes saturated beyond what it can hold. Once the sponge can no longer retain the extra ink, the excess liquid has nowhere stable to stay. It can migrate down to the printhead and leak. That is why overfilled sponge cartridges often drip from the nozzle area.

A spongeless BCH-style cartridge is different because it is not relying on sponge absorption to hold the ink. Instead, it relies on controlled air exchange and regulated internal pressure. The replacement cover helps prevent the cartridge from becoming either over-pressurized or fully open to atmospheric dumping. The cartridge must be sealed correctly so that ink does not simply drain out, but it also must breathe in a controlled way so ink can flow when the printer demands it.

This is where pressure balance matters.

If the cartridge is fully sealed with no air replacement, ink may flow briefly, but as ink leaves the cartridge, a vacuum forms inside. That vacuum resists further ink movement. Eventually, the printhead may become starved of ink, causing missing colors, blank prints, or nozzle dropout. This is the "vacuum stops it from working" problem you mentioned, and you are correct: too much vacuum is bad.

If the cartridge is too open to the atmosphere, the opposite problem occurs. Air can freely enter, and gravity can allow ink to move downward through the printhead. In that case, the cartridge can leak, especially if the printhead is lower than the ink chamber or if the cartridge is left sitting outside the printer. This is similar to what happened when you poured distilled water into an uncovered cartridge and left it overnight.

The correct design sits between those two extremes. It allows enough air exchange for ink to flow during printing, but not so much that the cartridge becomes an uncontrolled open tank. That is what the BCH replacement cover and its small pressure-regulating columns are designed to help with.

When pressure is applied to unclog a printhead, that pressure is temporary. It is used to push cleaning solution or ink through dried nozzles or restricted channels. Once the pressure source is removed and the cartridge is restored to its normal sealed-and-regulated state, the system should not continue pushing ink out endlessly. If ink continues to drip after pressure treatment, that usually means there is still excess positive pressure, a seal problem, an overfilled chamber, damaged nozzle plate behavior, or the pressure-regulating path is not functioning as intended.

In a properly assembled cartridge, ink does not continue to pour out because the cartridge is not being constantly pressurized. The internal chamber, printhead, meniscus at the nozzles, and controlled air path work together to stabilize the ink. The printhead nozzles are tiny, and liquid does not automatically gush out of them unless the pressure balance is wrong. Surface tension at the nozzle plate also plays a role. The ink forms a meniscus at each nozzle opening, and that surface tension helps resist uncontrolled dripping. However, surface tension alone cannot save a badly vented, badly sealed, overfilled, or incorrectly modified cartridge. The cartridge design still has to regulate pressure properly.

Your distilled water example is also important because water and ink do not behave exactly the same. Distilled water has a different viscosity and surface tension than ink. Printer ink is formulated to work with printhead nozzles, cartridge chambers, and capillary/pressure systems. However, even with proper ink, if you pour it into an open cartridge without the correct BCH cover, it can still leak. So the main issue in your test was not simply that the liquid was water. The larger issue was that the cartridge was open and lacked the proper pressure-regulating cover.

This is why we do not recommend thinking of the spongeless modification as "removing the sponge and filling an empty tank." That would be unreliable. The modification works only when the cartridge is converted into a controlled ink reservoir. The cover, refill holes, seals, and pressure regulator are all part of the system.

For Canon cartridges such as the PG-240, CL-241, PG-245, and CL-246, the printhead is built into the cartridge itself. That means the cartridge is not just an ink container. It is also the printhead assembly. Any issue with internal pressure, nozzle condition, electrical contacts, clogging, overheating, or air ingestion can affect printing. If the cartridge is modified incorrectly, you may see leaking, missing colors, poor flow, or cartridge failure.

A few common reasons a spongeless cartridge may leak include:

The BCH replacement cover is not installed or sealed correctly. If air enters from the wrong place, pressure regulation will fail.

The cartridge is overfilled. Even a regulated cartridge still needs proper air space and correct fill level.

The refill plug or refill hole is not sealed correctly. A loose plug can turn the cartridge into an uncontrolled vented tank.

The cartridge was pressurized too much during unclogging. Excessive pressure can force ink through the printhead and may continue dripping until pressure equalizes.

The printhead nozzles or internal filter area are damaged. A physically damaged printhead may not hold ink properly.

The cartridge is stored incorrectly outside the printer. Modified cartridges should be handled carefully and should not be left sitting in a way that allows gravity to encourage leakage.

The pressure-regulating column or air path is blocked, missing, damaged, or improperly assembled. This is especially important because the small white column on the BCH cover is not decorative; it is part of the functional design.

So, to answer the main concern directly: yes, if you remove the sponge and simply pour ink or water into the cartridge without a proper regulating cover, it can leak. That is not the BCH spongeless system working correctly. The BCH cover is what makes the modification practical. It helps regulate the pressure so that the cartridge does not behave like an open bottle of ink, while still allowing enough controlled airflow for the printer to draw ink when needed.

The science behind it is a balance of gravity, air replacement, surface tension, internal pressure, and controlled venting. Too much positive pressure causes leaking. Too much vacuum causes ink starvation. Too much open airflow causes dripping. The goal of the BCH spongeless design is to keep the cartridge in the usable middle range where ink can flow when the printhead demands it but does not freely drain when the printer is idle.

This is also why assembly details matter. A small gap, poor seal, wrong cover, missing plug, or damaged pressure regulator can completely change the behavior of the cartridge. The modification is not difficult once understood, but it does require that each part perform its intended function.

Addressing printer issues can be a complicated affair because many of these problems require hands-on inspection and testing. For that reason, we are not able to provide remote troubleshooting, suggestions, or support for individual printer repairs. We do offer an in-person evaluation and repair service through our local diagnostic facility, BCH Technologies Printer Repair Service [https://bchtechnologies.com/printer-repair-service]. Because demand is high, we handle repairs on a first-come, first-served basis, so it may take a few weeks before your printer can be dropped off. Our services are structured to repair either a complete printer or specific parts, with clear instructions on how to proceed. However, we understand that our rates may not be the most economical option for everyone. For that reason, we strongly recommend self-help through online research whenever possible. A good place to start is YouTube or our own YouTube channel homepage, BCH Technologies on YouTube [https://youtube.com/@bchtechnologies]. Once there, use the search icon next to "About" on the right-hand side of the menu bar to search for specific topics. I receive dozens of questions every day asking where to find videos on specific repairs or printer models. Since we have created videos for more than nine years, it is difficult to remember every single video by name. YouTube's search function is usually the fastest way to locate the most relevant video, and it may also recommend helpful videos from other creators.

Thank you again for asking such a detailed and fair question. It is completely reasonable to want to understand why the cartridge does not leak before deciding whether to purchase or attempt the modification. The short answer is that the cartridge must not be treated as an open tank. The BCH replacement cover, especially the small pressure-regulating column beside each refill hole, is what allows the spongeless design to control airflow and pressure so the cartridge can work properly.