What Is a Micro Exhaust Valve
A micro exhaust valve, also described as an automatic air release valve, is a small automatic air venting device fitted at high points in a pressurised pipeline. It is typically installed in high-rise buildings, factory piping systems and small pumping stations to protect or improve the water delivery efficiency of the system while saving energy. Its purpose is different from that of a large air valve used to admit or expel bulk air during filling and draining: the micro exhaust valve works continuously while the line is in service, releasing the small quantities of air that come out of solution as water is pumped.
In a typical installation, roughly two percent of the volume handled by the system is dissolved air. This air is progressively released as the water is delivered and accumulates at the higher points of the pipeline, where it forms pockets that restrict the flow area, raise the pumping head required and reduce the delivered flow rate. Continuous venting keeps those pockets from forming and keeps the hydraulic performance of the line close to its design condition.
Why Dissolved Air Has to Be Removed
Air pockets reduce the effective flow area, so the pump has to work against a higher head for the same delivered flow, which increases energy consumption.
Trapped air in a pump suction or discharge line can cause noisy operation, vibration and, in severe cases, loss of prime.
Air pockets create local oxygen concentration cells in steel and iron pipework, which accelerates internal corrosion and shortens pipe life.
Air in heating and cooling circuits reduces heat transfer at emitters and coils, so the system performs below design output.
Air in metering and control sections causes unstable readings and erratic control valve behaviour.
Technical Parameters and Materials
| Parameter | Specification |
|---|---|
| Nominal pressure | 1.0 MPa to 1.6 MPa |
| Nominal diameter | DN10 to DN25 |
| Applicable media | Water, oil and mildly corrosive liquids |
| Applicable temperature | 0 °C to 100 °C |
| Test standard | GB/T 13927 and API 598 |
| Body and cover | Cast iron, ductile iron, cast steel or stainless steel |
| Internal trim | Stainless steel float, stem and orifice components |
| Seal | Elastomer seat, selected for the medium and temperature |
| Connection | Threaded or small flanged end, matched to the tapping in the pipe or vessel |
Pressure testing of the body follows GB/T 13927 for industrial valves, with API 598 accepted as the alternative inspection and test standard for export projects. Because the valve is small, a plain shell test at the specified test pressure and a seat tightness test are sufficient to confirm that the casting and the seat are sound.
Construction and Operating Principle
The valve body contains a float, a stem and an orifice arrangement linked to a small sealing seat at the outlet. When air accumulates in the body, the liquid level falls, the float drops with it, and the outlet is opened so that the collected air escapes to atmosphere. As the air is discharged and liquid rises in the body, the float lifts and the outlet re-closes, so the valve returns to a sealed state and no water is lost.
This automatic cycle repeats continuously without any operator intervention and without an external power supply, which is the main advantage of the design: it removes air whenever air is present and stays shut whenever it is not. The orifice is deliberately small, so the volume of air released is controlled precisely and the loss of liquid during venting is negligible.
Features and Advantages
High-efficiency venting. The small orifice discharges air at a controlled rate and closes as soon as liquid reaches the float, so the medium loss during venting is negligible and the pipeline returns quickly to normal operation.
Stable performance. Corrosion-resistant body and trim materials give stable operation over long periods, including in damp plant rooms and lightly aggressive media.
Automatic operation. No manual intervention is needed, which removes the need for routine venting by an operator and reduces labour and outage time.
Compact and light. The valve is small enough to fit on a pipe tapping or vessel top, and it can be maintained in place.
Installation Positions
At high points and local summits of the pipeline, where air naturally collects.
On the discharge side of pumps and after long horizontal runs with an upward slope.
At the top of risers in high-rise buildings, where a suction effect can draw air out of solution.
On the highest point of closed heating and cooling circuits, and at the top of coils and heat exchangers.
Downstream of control valves and at points where pressure reduction releases dissolved air.
The valve must be mounted with its outlet vertical and clear of any obstruction, so that discharged air is not trapped behind insulation or a lagging jacket. An isolation valve below the unit allows the valve to be serviced without draining the line.
Applications
HVAC and building services, removing excess air from heating, cooling and domestic water circuits.
High-rise buildings and small pumping stations, protecting and improving water delivery efficiency.
Oil and gas facilities, where the valve keeps flow stable and prevents gas pockets in transfer lines.
Chemical plants, where accumulated gas raises pressure and can damage downstream equipment.
Pharmaceutical production, where controlled venting supports hygiene and process safety.
Food and beverage plants, where venting prevents contamination and helps hold product quality.
Maintenance and Fault Finding
Check the unit at annual intervals: confirm that air still escapes freely and that the outlet seals fully when liquid reaches it.
Clean the orifice and the seal seat, since scale and fine debris are the main causes of a valve that weeps continuously.
Renew the elastomer seat and any gasket at the recommended interval, and immediately if the valve drips after closing.
Isolate the valve before dismantling, and refit the float and stem without bending the stem, which would upset the closing level.
If the valve fails to vent at all, check that the tapping is not blocked and that the float is not held by debris or scale.
FAQ
Q: What is the difference between a micro exhaust valve and a bulk air valve?
A micro exhaust valve releases small continuous quantities of air that come out of solution while the line is running, whereas a bulk air valve admits or expels large volumes of air when the line is filled or drained.
Q: How much air does it remove?
In a typical pressurised water system, around two percent of the handled volume is dissolved air, and the valve releases that air steadily as it is liberated along the pipeline.
Q: Which standards apply?
Body pressure testing follows GB/T 13927 for industrial valves, with API 598 accepted for export projects, and the end connection is matched to the pipe or vessel tapping standard.
Q: What pressures, sizes and temperatures are available?
The usual range is PN10 to PN16, DN10 to DN25, for media temperatures from 0 °C to 100 °C, with water, oil and mildly corrosive liquids all suitable.
Q: Where should the valve be installed?
At high points and local summits of the pipeline, at the top of risers, on the discharge side of pumps and at the highest point of closed circuits, with the outlet vertical and clear of obstructions.
Q: What if the valve keeps dripping after it closes?
A continuous drip indicates contamination or damage at the seat, a worn elastomer seal, or scale on the float stem. Cleaning the seat and renewing the sealing element normally restores tight closure.