Tag Archives: water

This is what happens when an engineer with an insatiable curiosity, power tools, and clearly too much time on her hands changes the water filter inside her refrigerator. Yes, that is pretty much it. There really is no other point to this post. Most normal people would take the old water filter and throw it away. I am not a normal person, and I wanted to see inside it, so I cut it open. Warning and reassurance to my mom: I wore a half-face respirator with PM10/VOC filters, goggles, and a leather glove while I cut through the filter. I strongly recommend if anyone else tries this, you do this also. I didn’t want to breathe in the dust or get it in my eyes.

Here is the filter before I began.

Photo 1: Used water filter for my refrigerator, side view

Photo 2: Used water filter for my refrigerator, top view

Here is the cross section after I cut through it length wise.

Photo 3: Water filter after length wise cut

The filter consists of a plastic shell that contains a hollow, round-bottom, cylindrical carbon filter. It is kind of hard to see, but the middle of the carbon filter is hollow. The carbon filter is held in the center of the plastic shell, so that there is free space all around the filter. Here are the two halves of the carbon filter side by side with inside of one shown on the left, and the outside of the other shown on the right.

Photo 4: Two halves of the carbon filter, showing inside and outside

As you can see the inside is still very black while the outside has started to gray. I have a hypothesis for the reason, which I will get to soon.

Here is the plastic shell with the carbon filter removed.

Photo 5: Plastic shell of the filter

Now here is a close up of the inside top of the plastic shell.

Photo 6: Close up of the inside of the top of the plastic shell of the filter

Notice how there are channels formed radiating from the center? The filter only has one opening, the hole in the center in the top, as is shown in the second photograph. Thus, one of the reasons I cut the filter apart was to try to figure out how it works. Water goes in through the center, but how does it get out? What follows is my engineering guess as to how it works. I am fairly sure the water comes in through the center hole, and the water pressure in the house forces it into the hollow center of the carbon filter and then through the carbon in all directions radiating outward. The water then is stored on the outside of the carbon filter until it is pulled by the refrigerator’s water dispenser or the ice maker. I think the white matter that has formed on the outside of the carbon filter that gives it a grayish appearance is calcium and magnesium, otherwise known as hardness. I live in Arlington County, Virginia, and our latest water report lists our water’s hardness as 125 mg/l. According to the United States Geological Survey, that puts our water as just in the hard range.

So if the water is stored on the outside of the carbon filter, how does it leave the filter to get to the water dispenser or ice maker? That is where I think those channels at the top of the plastic shell come in. In Photo 3, you can see the plastic top of the carbon filter fits flush with the top of the plastic shell, but the top of the plastic shell has those channels. Because of the space between the plastic shell and the carbon filter, the water can enter the channels from the outside then flow through the channels back to the hole in the center. However, the now filtered water does not flow back the same hole where the unfiltered water enters.The plastic tube at the top of the carbon filter prevents the filtered water from going back into the filter. Instead the filtered water leaves next to the center hole. In Photo 2, two rectangles can be seen next to the center hole, at approximately 1 and 6 o’clock in the photo. Those rectangles are holes, and it appears that the water that flows through the channels then can exit the filter through those rectangular openings. I can’t tell exactly this happens even though I examined where the filter attaches in the refrigerator. I did consider that perhaps I have the flow direction completely opposite, that is that the water enters through the rectangles, flows through the channels into the open space, then is forced through the carbon filter into the center of the filter. There are a variety of reasons, geometry, fluid dynamics, water pressure, etc., why I am fairly sure this is not the case.

So that is how my refrigerator’s water filter works. See this was educational. It was not just about me having fun with my Dremel rotary power tool and destroying something. Really it wasn’t.