How do air separators remove air from water

The Air Separator

Circulators move water around a hydronic system pretty quickly. In many cases, water is whipping through the pipes at speeds up to four feet per second! Think of it. Water is in and out a 12-foot-wide room in just three seconds.
And you know there’s more to that flow than just water – there’s also air. Air is a problem because your customer can hear it pinging around in the system. No one likes to live with noisy radiators. Noisy radiators lead to call-backs for you.

To make matters worse, this air usually gets trapped in the radiators out at the far ends of the system where it often stops the flow of heat entirely. No one likes to live with cold radiators, so you get another call-back.

Where does the air come from? It’s in the cold water when you first fill the system. It’s dissolved in solution, and cold water holds a lot more air that hot water. When you heat the water, the air comes out of solution and starts to whip around the system like BBs. If you vent the air, the system pressure will drop. You’ll have to add more cold water to bring the pressure back up to it’s normal level, and when you do, you’ll be letting even more air into the system.

But this doesn’t have to be a big problem. All you have to do is catch the air before it has a chance to get out into the system. That’s where the air separator comes in.

AS also stands for “It ain’t the same!”

Bell & Gossett’s IAS air separator has no moving parts. It uses air’s natural buoyancy to get the job done. Let’s take a look inside one.

IAS stands for Inline Air Separator. It has two chambers, and it’s a bit wider than the pipe it serves. We separated the two chambers with an orifice, and therein lies the secret to the IAS’s great performance.

An orifice is a hole that’s a bit smaller than the chamber itself. Air-laden water flows down the pipe and enters the “wide space in the road” – the IAS. Naturally, as the water widens out in the IAS, it also slows down. That slowing motion releases the air bubbles in the same way a slowing river current releases floating debris.

The air bubbles quickly float to the top of the first chamber and get trapped by the wall of iron that makes up the orifice and flows to the radiators. Since the IAS snatches the air out of the flow just as it leaves the boiler; the air doesn’t get a chance to create problems out in the system.

Once captured, the IAS vents the air out of the system through an automatic air vent, which you’ll install in the IAS’s top tapping. If you’re using a plain steel compression tank, the IAS will pass the air up into the tank.

An imagination exercise…

A good way to picture the IAS’s operation is to imagine that you’re in a room with a few dozen helium-filled balloons and an electric fan. The room has a door that leads to another room of a similar size.

Now, imagine that the room you’re in is the IAS air separator and that the door is the orifice. The balloons represent the air bubbles.

When you let go of the balloons, they’ll rise to the ceiling because helium is lighter than air (just as the air bubbles in our heating system will rise because they’re lighter than water).

Now turn on the fan to simulate the flow of water through the air separator. Point the fan at the door (the orifice) that leads to the other room. Do the balloons escape from the first room? No, they can’t, can they? They’ve been trapped by the wall above the doorway – just as the air bubbles in the IAS are trapped by the wall of iron above the orifice.

We use the second chamber in the IAS to make sure a whirlpool doesn’t form at the center of the orifice. Going from a wide space to a narrow space and then again back to wide space creates a “quiet zone” just above the inlet to the orifice. That second chamber on the outlet side of the orifice keeps the air from being sucked into the system. Beautifully simple, isn’t it?

“Scoops” are different

Other types of air separators use an inclined plane to remove air. These are commonly called “air scoops.” We decided to use the orifice design instead of the “scoop” design for the IAS after extensive testing in our research lab convinced us that an orifice removes more air on each pass. We figured the more air we could catch the better. Makes sense, doesn’t it? (That’s why IAS also stands for “It Ain’t the Same!”)

That top tapping in the IAS is 3/4″ We decided on a 3/4″ tapping instead of the 1/8″ tapping you’ll find on the “scoops” because we wanted you to have as many options as possible. With a ¾” tapping, you can use either a residential or a commercial type of air vent. Its your choice.

And because the tapping is 3/4″ and not 1/8″, you can also use the IAS air separator with a steel compression tank if you wish. Many times those tanks are there in the basement already. They’re free! Why not take advantage of them? We figure the choice should be yours. And doesn’t it make sense that air will leave the system piping faster through a 3/4″ opening than it will through a 1/8″ opening? That’s why we gave it to you.

The bottom tapping on the IAS is 1/2″. You can use this tapping to connect either the diaphragm tank (if you’re using a diaphragm tank) or the feed valve. Again, the option is yours.

Any hot water heating system can be made better with an air separator such as the IAS. It does a find job, and it doesn’t cost a fortune.

Remember, automatic air vents installed at the high points of a system can’t effectively remove entrained air bubbles from the high-speed flow we see in modern hydronic systems. You have to snatch those bubbles out of the flow. And that’s exactly what the IAS does.