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What exactly is the function of the exhaust valve in the HAVC system?

2026-05-29

What is an Air Valve?

An Air Valve (also known as an automatic air release valve or automatic air vent) is a small, self-operating device designed to automatically release trapped air from a liquid-filled piping system while preventing liquid from escaping. In HVAC and plumbing systems, air pockets can form at high points in pipelines, causing reduced flow efficiency, noise, corrosion, and water hammer. The air valve solves this problem by venting accumulated air automatically — without any manual intervention or external power.

The operating principle is simple and ingenious:

* The valve contains a float mechanism (usually a hollow ball or cylindrical float) that rises and falls with the liquid level

* When air accumulates in the valve body, the liquid level drops, causing the float to descend

* As the float descends, it opens a small orifice (vent port) , allowing trapped air to escape

* When liquid re-enters the valve body, the float rises and seals the orifice , preventing liquid from leaking out

* The cycle repeats automatically whenever air accumulates

Key characteristics of Air Valves:

Fully automatic operation – No manual intervention, no external power required

Compact size – DN15 to DN25 (½" to 1") — fits easily at pipeline high points

Continuous air release – Releases small pockets of air as they accumulate during normal system operation

Sealed construction – Prevents leakage when the system is under pressure

Maintenance-free – Simple float mechanism with long service life

Brass construction – Corrosion-resistant for water and mild chemical service

At WEIZIDOM, our Air Valves are manufactured to ISO228 design standards with strict quality control (12 tests from raw material to final product), ensuring reliable, automatic air release for water, gas, and other liquid-filled systems.

Main Function in HVAC Systems

In HVAC systems, the Air Valve serves as an essential air management device that removes trapped air from liquid-filled piping systems, improving efficiency, reducing noise, and preventing damage.

Its primary functions include:

Function	Description
Removing Trapped Air from Chilled Water Lines	Air pockets in chilled water pipes reduce cooling capacity, create flow noise, and cause uneven cooling. Air valves installed at high points automatically vent this air, ensuring efficient system operation.
Venting Air from Hot Water Heating Lines	Air in hot water systems causes gurgling noises in radiators, reduces heat output, and can lead to pump cavitation. Air valves release air from radiators, baseboard heaters, and main supply lines.
Preventing Air Locks in Pumped Systems	Accumulated air can create air locks that block flow entirely — preventing water from reaching terminal units. Air valves break air locks by releasing trapped air at strategic high points.
Reducing Corrosion by Removing Oxygen	Dissolved oxygen in water accelerates corrosion of pipes and equipment. By venting air from the system, air valves reduce the oxygen content, extending the service life of the HVAC system.
Eliminating Water Hammer from Air-Related Surges	Compressed air pockets can suddenly release, causing pressure surges (water hammer) that damage pipes and fittings. Air valves prevent this by removing air before it can accumulate.
Facilitating System Start-Up & Filling	When filling an empty HVAC system, air must be displaced by water. Air valves automatically vent this air during filling, allowing complete and rapid system fill without manual bleeding.

Typical applications within water and gas systems include:

Application Field	Specific Use
Chilled Water Systems	High point vents on supply and return mains, air separator vents
Hot Water Heating Systems	Radiator vents, baseboard heater vents, boiler air vents, main line high point vents
Hydronic Piping	Air separator vents, expansion tank connections, pump suction line vents
Solar Thermal Systems	High point vents on collector loops, storage tank connections
Geothermal Heat Pump Loops	High point vents on ground loops, buffer tank connections
Water Supply Lines	High point vents in building water distribution, pressure tank vents
Compressed Air Systems	Drain points for condensate and air release (note: for liquid lines, not dry air lines)

Key Features & Advantages

WEIZIDOM’s Air Valve is engineered specifically for HVAC and plumbing systems, providing automatic, maintenance-free air release.

Below are its outstanding features and advantages:

Feature	Advantage
ISO228 Compliance	Manufactured to international thread standard for pipe threads — ensures compatibility with standard BSP or BSPT threaded pipe fittings worldwide.
Compact Diameter Range (DN15–DN25 / ½"–1")	Small size fits easily at pipeline high points, radiator tops, and air separator outlets — installs in tight spaces without interfering with other equipment.
Pressure Rating 0–1.6MPa (0–232 psi)	Suitable for typical HVAC system pressures — chilled water (0.6–1.0 MPa), hot water (0.4–1.0 MPa), and hydronic systems (up to 1.6 MPa).
Fully Automatic Operation — No Power Required	Float mechanism operates purely by buoyancy — no electricity, no sensors, no controls. Installs and forgets — vents air automatically whenever it accumulates.
Brass Construction — Corrosion Resistant	High-quality brass (copper-zinc alloy) provides excellent resistance to rust, scaling, and dezincification in water and steam service. Durable, long-lasting, and compatible with water treatment chemicals.
Threaded Ends for Easy Installation	Female threaded ends (BSP or NPT) allow direct connection to standard threaded pipe or equipment ports — no welding, no flanges, no special tools. Quick installation at any high point.

Additional advantages that support WEIZIDOM's overall value proposition:

Bubble-Tight Sealing – Precision float and orifice design prevents water leakage when the valve is closed — no drips, no wasted water.

Quiet Operation – Smooth float movement and controlled air release minimize noise — no hissing or chattering.

Maintenance-Free – Simple mechanical design with no moving parts except the float — no adjustments, no lubrication, no regular service required.

Multiple Mounting Orientations – Can be installed vertically (preferred) or at an angle — flexible installation options for high points with limited space.

Integrated Strainer (Some Models) – Built-in fine mesh strainer prevents debris from blocking the orifice — ensures long-term reliability.

Manual Test/Release Valve – Some versions include a manual release screw for testing or manual venting during system fill.

Temperature Rating – Suitable for chilled water (4–15°C) and hot water (50–90°C) — compatible with glycol mixtures up to 50%.

Compact, Lightweight – Easily installed by one person — reduces labor cost.

Rigorous Quality Control – Each valve undergoes 12 tests from raw material to final product, including float operation verification, pressure testing, seat leakage test, and dimensional inspection.

How an Air Valve Works

Normal Operation (System Under Pressure, No Air):

Air Release Mode (Air Accumulates, Float Drops):

Cycle:

* Air accumulates in the valve body at the system high point

* Water level drops as air displaces water

* Float descends with the water level

* Float opens the vent orifice — air escapes

* Water re-enters the valve body

* Float rises and seals the orifice — cycle repeats

Why Choose WEIZIDOM’s Air Valve for Your HVAC System?

Reason	Benefit
Essential for HVAC System Efficiency	Removes trapped air that causes noise, reduces heat transfer, creates air locks, and accelerates corrosion — improves system performance and reliability.
Fully Automatic — No Maintenance	Float mechanism operates automatically without power or intervention — install and forget.
ISO228 Compliant	Manufactured to international thread standard — ensures compatibility with standard BSP/BSPT threaded fittings worldwide.
Compact Size (DN15–DN25)	Fits easily at pipeline high points, radiator tops, and air separator outlets — installs in tight spaces.
Brass Construction — Corrosion-Resistant	Resists rust and scaling in HVAC water systems — longer service life than plastic or iron alternatives.
Cost-Effective Air Management	Low initial cost plus no operating cost (no electricity) — rapid payback through improved system efficiency and reduced maintenance.
5 Domestic Factories	Located in Tianjin, Wenzhou, Hebei, Lianyungang, and Shandong, ensuring consistent quality, competitive pricing, and fast delivery.
108+ Export Destinations	Proven reliability in countries including Mexico, Colombia, Chile, Pakistan, Saudi Arabia, UAE, South Africa, Egypt, and more.

Technical Specifications

Parameter	Specification
Design Standard	ISO228 (Pipe Threads for General Purpose)
Diameter Range (DN)	DN15, DN20, DN25 (NPS ½", ¾", 1")
Pressure Range	0 – 1.6 MPa (0 – 232 psi)
Medium	Water, water-glycol mixtures, air (from liquid systems)
Body Material	Brass (Cu-Zn alloy) — dezincification-resistant
Float Material	Brass (hollow) or corrosion-resistant polymer
Seat / Orifice Material	Brass (precision-machined)
Internal Spring (if applicable)	Stainless Steel
End Connections	Female threaded — BSP (ISO228) or NPT (ASME B1.20.1) — as specified
Mounting Orientation	Vertical (preferred) — float mechanism requires upright orientation
Operation	Fully automatic — no external power required
Vent Orifice Size	Small (typically 1–3mm) — for continuous air release
Sealing Type	Float-to-seat — bubble-tight when closed
Testing Standards	ISO 5208 / EN 12266
Hydrostatic Test Pressure	1.5 × rated pressure (2.4 MPa)
Seat Leakage	Zero (bubble-tight)
Temperature Range	0°C to +100°C (standard); up to +120°C (high-temp version)
Minimum Operating Pressure	0.02–0.05 MPa (2–5 psi) — allows venting even at low pressures
Maximum Operating Pressure	1.6 MPa (16 bar / 232 psi)
Applicable Media	Chilled water, hot water, water-glycol mixtures (ethylene glycol, propylene glycol up to 50%), mild water treatment chemicals
Body Finish	Natural brass (uncoated) or nickel-plated — as specified

Customized options (NPT threads, nickel-plated finish, high-temperature version, integrated manual vent, larger orifice for faster venting) available upon request.

Installation Notes for HVAC Systems

To ensure proper operation of the Air Valve:

Installation Guideline	Reason
Install at the highest points of the piping system	Air naturally rises to high points — installing elsewhere may not capture all trapped air.
Install vertically with the vent cap pointing UP	Float mechanism requires vertical orientation to operate correctly.
Install an isolation valve (ball valve or gate valve) below the air valve (recommended)	Allows removal or replacement of the air valve without draining the entire system.
Do not install in locations subject to freezing	Ice can damage the float and body — install in conditioned spaces or use heat tracing.
For systems with dirty water or debris, install a strainer upstream	Debris can block the small vent orifice — strainer extends service life.
For systems with high air content (during initial fill), consider larger or multiple air valves	Standard air valves are designed for continuous release of small air pockets — large volumes may require additional venting.
Allow adequate clearance for air discharge	Vent must be open to atmosphere — do not install in enclosed spaces where escaping air or water spray could cause damage.
For glycol mixtures, verify compatibility with brass	Standard brass is compatible with most ethylene and propylene glycol mixtures up to 50%.

Air Valve Placement in HVAC Systems — Typical Locations

Location	Reason	Recommended Size
High points on supply and return mains	Air accumulates at high points in main distribution piping	DN20–DN25 (¾"–1")
Top of radiators	Individual radiator air venting	DN15 (½")
Top of air separators	Captures air separated by centrifugal action	DN20–DN25 (¾"–1")
Pump suction line high points	Prevents air from entering pump	DN15–DN20 (½"–¾")
Expansion tank connections	Vents air from expansion tank	DN15–DN20 (½"–¾")
Vertical riser tops	Air accumulates at top of riser before horizontal turn	DN20–DN25 (¾"–1")
Coil connections (AHU/FCU)	Local air venting at terminal units	DN15 (½")

Symptoms of Trapped Air in HVAC Systems

Symptom	Cause	Solution
Gurgling or bubbling noises in pipes	Air moving through water	Install air valves at high points
Reduced heat output from radiators	Air pocket blocks water flow	Vent air from radiators
Uneven cooling from fan coil units	Air in chilled water lines	Install air valves at system high points
Pump cavitation noise	Air entering pump suction	Vent air from pump suction line high points
Water hammer (banging pipes)	Trapped air compressing and releasing	Remove air from system
Difficulty filling system	Air lock preventing water flow	Vent air during filling process
Corrosion / black water	Oxygen in water causing rust	Remove air to reduce oxygen content

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