Automatic air vent

johnjohn89

Hydronic experts! Someone said automatic air vents cause problems when work individual,have to be work with air scoop ,mounted on the top of air scoop! But why? They both got same function to remove air in the boiler! Why automatic air vents can’t work individually? 

mattmia2

It depends on what you are trying to accomplish. Don't need some method to collect air if you are just trying to remove air form a high spot that is difficult to access so you can get flow started.

If you are trying to eliminate all the air from the system at the boiler, you need some method to encourage the air to collect at the vent.

The first thing is to pick the place where the air is most likely to come out of solution so where the water is the hottest where it has just come out of the boiler.

The second thing is to pick the place with the least pressure so on the suction side of the circulator.

An air scoop is just a casting with a larger inner chamber size than the pipe to slow down flow and encourage air to rise up out of the fluid at that point to an automatic vent in the top of the scoop.

A modern air eliminator is a microbubble scrubber type air remover. It has a chamber to slow down the flow but it also has a metal or plastic mesh inside it to encourage the small air bubbles to stick to that mesh and combine with other small bubbles that form larger air bubbles that have enough force to break away from the mesh and rise up to the automatic vent on top of the device. An example would be a Spirovent or Caleffi Discal.

There is an Idronics that covers this.

mattmia2

Also note that a system with a conventional compression expansion tank instead of a diaphragm expansion tank should not have any automatic air vents because they will remove the air from the expansion tank.

ratio

If the system pressure at an automatic air vent goes below atmosphere pressure (due to, say, a circ coming on), an automatic air vent will allow air back in to the system, unless it's been closed (so it doesn't work automatically).

EdTheHeaterMan

johnjohn89 said:

Hydronic experts! Someone said automatic air vents cause problems when work individual,have to be work with air scoop ,mounted on the top of air scoop! But why? They both got same function to remove air in the boiler! Why automatic air vents can’t work individually? 

I'm going to take a stab at this one... Air vent on the top of the air scoop works better that Air vent on the bottom of the air scoop. The reason is that air is lighter than water so it is going to be at the top of the air scoop. Putting the air vent at the bottom of the air scoop might make the air vent upside down and all the water will leak out of the system.

Now who is going to clean up that mess?!?

I hope this helps
Mr. Ed

EdTheHeaterMan

On the serious side, if you have an air vent at the top of the system. We are talking on the top floor at the highest radiator or pipe in the system.
And you have an old boiler where the circulator was installed on the return near the boiler. (or an new boiler installed by an old guy that dose not like change)
And the static pressure of the boiler is just enough to get the air out of the system when the boiler is not operating.
Then the boiler operates and the pump turns on and the head of the pump creates a lower pressure on the inlet side of the pump.
And that lower pressure makes the water pressure at the top of the system lower. low enough to drop the pressure at the top of the system below the air pressure of the atmosphere. (Think of lifting an inverted glass of water from a basin. the water stays in the upside down glass until you break the vacuum)
Then the higher pressure air at that top of the system vent will cause the vent to open and let air in at that point. (now think of that same inverted glass with a hole in it. As you lift the inverted glass out of the water basin, the hole in the glass will let air in. That is what your air vent can do.)

Not such a good use of an air vent You want the air to go out... not go in.

The next problem is that most of the air bubbles in a heating system are so small the when the pump operates those bubbles don't find their way to the top of the pipe and will just rush on past the tiny Tee fitting with the air vent just sitting there doin' nothin' while all the air passes by.

The air scoop is designed to take those smaller bubbles of air that are rushing around the pipes and slow then down in the air scoop. the slower moving bubbles can now float to the top of the scoop where there is an air vent just waiting for them to accumulate and be released from the system to the atmosphere.

GGross

Keep in mind the air scoop needs a length of horizontal pipe on it's inlet side, this is because the air in the horizontal pipe will travel on the top of the pipe, allowing it to be "scooped".



If you use a brass air separator like the caleffi models they have a coalescing media inside of them which encourages the air to escape the water without relying on the air sitting nicely on top of the pipe.