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Air Vent for Liquid Systems: Working Principle and Selection

Learn how automatic air vents remove air from water and liquid lines, the benefits they bring and how to select the right one.

ORFA Technical TeamUpdated: Oct 30, 20263 min read

Float-operated automatic air vent for liquid systems

In pipework carrying liquids, especially hot and cold water circuits, air and other undissolved gases gradually collect at the high points of the system. This blocks circulation, accelerates corrosion and causes noise and pump wear. An air vent for liquid systems discharges the accumulated air automatically, keeping the system efficient, quiet and safe.

This article explains how these air vents work, the benefits they bring, where they are used and what to check when selecting one.

What Is an Air Vent for Liquid Systems?

An air vent for liquid systems (air eliminator for liquid circuits) is a valve that automatically releases air and non-condensable gases collecting in pipelines and equipment. It usually works with a float mechanism: as the liquid level inside the valve body changes, the float moves and opens or closes the vent orifice. Only air is discharged; the liquid stays in the system.

Working Principle

Air accumulation: Air carried by the fluid collects at the high point where the vent is installed.
Level drop: The air gathering in the vent body pushes the liquid level inside it down.
Float movement: As the liquid level falls, the float drops.
Valve opens: The falling float opens the vent orifice and the accumulated air is released.
Valve closes: As the air escapes, liquid refills the body, the float rises and closes the orifice, preventing any liquid loss.

The cycle repeats automatically whenever air arrives; no operator intervention is needed.

Benefits

Uninterrupted circulation: With air pockets removed, the fluid circulates freely and heat transfer in heating and cooling circuits improves.
Less corrosion: Removing air, and therefore oxygen, from the system lowers the corrosion risk.
Less noise and vibration: Flow noise and vibration caused by air bubbles are reduced.
Equipment protection: Pump efficiency loss and wear caused by entrained air are prevented.
Automatic operation: Manual bleeding is no longer needed, reducing the maintenance workload.

Tip: Install air vents vertically at the highest points where air is expected to collect, such as the tops of risers and headers. Fitting an isolating valve upstream lets you remove the vent for maintenance without draining the system.

Applications

Hot water boilers
Heating systems
Cooling and chilled water systems
Tanks and vessels that are filled and drained
Industrial process circuits

Technical Points for Selection

The right air vent is selected according to the fluid, operating pressure and temperature, and connection size. The models in our product group generally offer the following options:

Feature	Options
Body and cover material	Ductile iron, brass, stainless steel
Internals	Stainless steel
Connection type	Threaded, flanged
Pressure, temperature and size	Depend on the model; check the product datasheet
Example model: Ayvaz HA-51	GGG40.3 ductile iron body, stainless steel float and internals, PN16, –10 °C to +250 °C, 1/2″ – 1″ (DN15 – DN25)

The maximum allowable operating pressure of the vent must not be lower than the highest system pressure. Float-type air vents can only open up to a certain maximum differential pressure, and this value must also cover the system operating pressure.

Frequently Asked Questions

Where should an air vent be installed?

At the highest points where air collects, for example the tops of risers, on headers and at boiler outlets, mounted vertically.

Does an air vent leak liquid?

A correctly working float-type vent does not. When the body fills with liquid, the float rises and closes the orifice, so only air and gases are discharged.

Is an air vent for liquid circuits the same as a liquid drainer for air circuits?

No. An air vent for liquid circuits removes air from liquid lines such as water systems. A liquid drainer for air circuits removes water that collects in compressed air lines.

Conclusion

Air vents for liquid systems prevent air accumulation and protect circulation, heat transfer and equipment life. To choose the right model, browse our air vents for liquid circuits product group, or contact ORFA at [email protected] for technical support.

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