Auditing an air pump

Saturday, August 04 2007 @ 07:43 AM PDT

Contributed by Windell

In order to qualify the CandyFab for culinary applications a few things have to happen. First and foremost, the sugar (or other print medium) has to be treated like food. That means only handling the sugar with clean hands, not sweeping it up off the floor and putting it back in the bucket of sugar, and so on. That part is pretty straightforward. Secondly, we have to understand what we're doing to the food, and make sure that the process is safe. Because all we're doing is heating the sugar, there is fundamentally very little to go wrong. One possible concern, however, is that we have an unknown element, a "black box" in the process: the air pump.
We don't expect our air pump to be spewing out toxins like crazy. In fact, it stands to reason that an aquarium pump is probably a fairly safe place to starting place, just from the idea that it's supposed to not kill your fish. (Keep in mind that some types of fish can be killed pretty easily by chemical contamination.) However, we do need to know what's going on in there, so we opened ours up for a very careful look.

Our pump is a Hagen Elite 799 air pump, $5 at big box pet stores. It's a very light duty air pump that delivers 1 L/minute at 1 PSI. Its siblings, the Elite 800-803 pumps, range up to 3.5 L/minute at 4 PSI at $10.00.
Obviously, we're starting with a brand new pump here-- don't take the one off of your aquarium!

It's remarkably easy to access the insides of this pump. The no-slip rubber base is held on by five normal screws-- a rarity for a $5 piece of consumer electronics. Note that the base is not air-tight, nor is it necessarily required for the pump to function. It does keep your fingers safe and prevent the unit from sliding around.

With the bottom cover removed, you can see pretty much all there is to see. The power cord enters at the right. It goes directly to a magnetic field coil wrapped around a "U" shaped laminated magnetic pole piece. As the 60 Hz AC goes through its cycle, it induces a magnetic field in the pole piece that alternately pulls a ceramic magnet towards one or the other end of the "U." The ceramic magnet is on the end of a metal bar that is able to move on a flexible rubber hinge, and the middle of this bar pushes and pulls on the pump diaphragm. It's a very simple AC motor. (You have seen the simple DC motor, right?)
The rubber hinge and diaphragm are attached to a small plastic box that contains the valves for the pump, and its output is the little tube at the bottom of the picture. The air gap around the output tube actually serves as the primary air intake for the system. So far, so good.

The pump assembly (consisting of the magnet, bar, diaphragm and pump body with the valves) slips out easily without any tools.

Here is what the pump assembly looks like up close. At the top is the metal bar with the ceramic magnet on the left hand side. The attachment point in the middle (with the screw end and nut) is the hinge point. The piece of black rubber that that the bar is hinged to is the diaphragm, and the hard plastic pump body is on the bottom. (The diaphragm in a pump like this will eventually wear out, and you can actually buy a rebuild kit (~$1) for this pump that consists of the assembly shown in this photo.)

The rubber diaphragm pops off easily to reveal the inside of the pump body with its intake and outlet valves.

Before we start to get picky, let me say that if I were to design an air pump for use with food, it would look exactly like this. They have, to a very good degree, done everything right. The design is painfully simple, and there is very little to go wrong. It is a completely dry design. There are not any apparent chemicals or lubricants present besides the chemical softeners in the plastic and rubber-- and no reason to suspect that there would be.
Now, to get picky: The rubber itself *is* a little smelly, a bit like bike inner tubes or other low-grade black rubber. That means that it's probably something like neoprene or butyl rubber. These types of materials (in low grades) are not considered to be "food safe" material. But, names like "food safe" apply when food is in *contact* with the material, not just sitting near-- sharing air with-- the material. Since no food is not actually coming into contact with the rubber, it's not obvious that there is any actual issue with that either. On the other hand, we're actually blowing air on the sugar as it melts. Perhaps that's the sort of gray area that we should expect with experimental cooking technologies.
In any case, the pump looks very good overall. My verdict and summary: I'd eat food prepared with this.
Does anyone else have thoughts to add?

Comments (19)

The CandyFab Project
http://www.candyfab.org/article.php/elite799

	Our pump is a Hagen Elite 799 air pump, $5 at big box pet stores. It's a very light duty air pump that delivers 1 L/minute at 1 PSI. Its siblings, the Elite 800-803 pumps, range up to 3.5 L/minute at 4 PSI at $10.00. Obviously, we're starting with a brand new pump here-- don't take the one off of your aquarium!
	It's remarkably easy to access the insides of this pump. The no-slip rubber base is held on by five normal screws-- a rarity for a $5 piece of consumer electronics. Note that the base is not air-tight, nor is it necessarily required for the pump to function. It does keep your fingers safe and prevent the unit from sliding around.
With the bottom cover removed, you can see pretty much all there is to see. The power cord enters at the right. It goes directly to a magnetic field coil wrapped around a "U" shaped laminated magnetic pole piece. As the 60 Hz AC goes through its cycle, it induces a magnetic field in the pole piece that alternately pulls a ceramic magnet towards one or the other end of the "U." The ceramic magnet is on the end of a metal bar that is able to move on a flexible rubber hinge, and the middle of this bar pushes and pulls on the pump diaphragm. It's a very simple AC motor. (You have seen the simple DC motor, right?) The rubber hinge and diaphragm are attached to a small plastic box that contains the valves for the pump, and its output is the little tube at the bottom of the picture. The air gap around the output tube actually serves as the primary air intake for the system. So far, so good.
	The pump assembly (consisting of the magnet, bar, diaphragm and pump body with the valves) slips out easily without any tools.
	Here is what the pump assembly looks like up close. At the top is the metal bar with the ceramic magnet on the left hand side. The attachment point in the middle (with the screw end and nut) is the hinge point. The piece of black rubber that that the bar is hinged to is the diaphragm, and the hard plastic pump body is on the bottom. (The diaphragm in a pump like this will eventually wear out, and you can actually buy a rebuild kit (~$1) for this pump that consists of the assembly shown in this photo.)
	The rubber diaphragm pops off easily to reveal the inside of the pump body with its intake and outlet valves.
Before we start to get picky, let me say that if I were to design an air pump for use with food, it would look exactly like this. They have, to a very good degree, done everything right. The design is painfully simple, and there is very little to go wrong. It is a completely dry design. There are not any apparent chemicals or lubricants present besides the chemical softeners in the plastic and rubber-- and no reason to suspect that there would be. Now, to get picky: The rubber itself is a little smelly, a bit like bike inner tubes or other low-grade black rubber. That means that it's probably something like neoprene or butyl rubber. These types of materials (in low grades) are not considered to be "food safe" material. But, names like "food safe" apply when food is in contact with the material, not just sitting near-- sharing air with-- the material. Since no food is not actually coming into contact with the rubber, it's not obvious that there is any actual issue with that either. On the other hand, we're actually blowing air on the sugar as it melts. Perhaps that's the sort of gray area that we should expect with experimental cooking technologies. In any case, the pump looks very good overall. My verdict and summary: I'd eat food prepared with this. Does anyone else have thoughts to add?