Mysteries Unveiled
What you are looking at is the inside bottom of a HP 51641A cartridge that has been cut away.
If you have ever refilled one of these, you are always wondering, what is inside this thing?
The print head is built in the shape of a cube and molded into the black plastic housing.
Only the bottom face of this cube is on the outside of the cartridge, the part with all of
the ink jets on it. This is where the ink comes out. You can't see this in the above photo.
The top of the cube (print head) has a filter screen on it where the magenta ink comes in.
In the above photo we have labeled this "magenta". Notice that the filter screen has been
damaged in the photo.
On the right side of the cube (print head) is the filter screen which lets in the cyan ink.
We have labeled this "Cyan". No damage here.
On the left side of the cube is an identical filter screen that lets the yellow ink come in.
We have labeled this "Yellow". You can't see the yellow filter screen due to the
angle the photo was taken on.
Each color has its own chamber defined by the "Chamber Walls". Inside each chamber there is a
rather dense sponge. The purpose of the sponge is to retain ink without flooding or
pressurizing the print head. The print head draws ink from the sponge on demand.
What Can We Learn Here ?
First of all, when you are trying to get your needle to the bottom of the magenta chamber, don't
press real hard or you will puncture the filter screen. The filter screens are made of stainless
steel and are very rugged, so you would have to push with a lot of force or speed to damage them.
When filling the cyan and yellow, you don't have to worry about damaging the filter screens, there
is no way a needle tip could come in contact with them.
In the magenta chamber the needle will not go as deep as it does in the cyan and yellow chambers.
Our 4" needle will have only 1/4" of metal exposed when it is in contact with the bottom of the
yellow or cyan chambers. In the magenta chamber, there will be 3/4" of metal exposed when you
are touching the filter screen with the tip of the needle.
By exposed metal, we mean the metal part of the needle that is still showing when you have it
inserted all the way into the cartridge. Putting the tip of the needle all the way in and making
contact with the bottom of the cartridge is very important. If you are not all the way down, an
air pocket will be created in the sponge, making the cartridge print intermittently.
Like they say, a picture is worth a thousand words. We just thought we would show you this
view of the insides. Very interesting isn't it.
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