Air Valves in Piping Systems

Air release valves are integral components in pipeline systems as they eliminate trapped air. While most individuals are familiar with their function, there exists a diverse array of air valves that serve specific purposes. These include unique designs tailored for wastewater applications and can accommodate sizes up to NPS 20. To protect piping systems from air-related issues, it is essential to understand how to properly select and install the appropriate air valves.

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Differentiating Types of Air Valves

According to the American Water Works Association (AWWA) Standard C512, three fundamental types of air valves are utilized within water and wastewater systems:

• Air-Release Valves
• Air/Vacuum Valves
• Combination Air Valves

AWWA air valves are manufactured using iron or stainless steel bodies with trims that resist corrosion, suitable for both water and wastewater services. It is crucial to note that these air valves serve distinct functions compared to pressure and vacuum relief valves. The latter are typically mounted on gas or steam pressure vessels and liquid storage tanks for overpressure protection. Such relief valves have specific preset thresholds and are not within the focus of this article. The air valves discussed here facilitate the automatic management of air or gas flows in liquid piping systems under various operational scenarios.

Air Release Valves

Understanding Air/Vacuum Valves

Air/vacuum valves are commonly applied for the discharge of air from vertical turbine pumps. Following a pump shutdown, air fills the piping between the pump and the check valve. Upon restart, the vertical turbine pump must evacuate this trapped air before water can flow into the check valve. An air/vacuum valve is ideal for this scenario, as it rapidly expels significant volumes of air and shuts when liquefied flow fills the valve.

An optional slow-closing device can be integrated into air/vacuum valves. This feature is particularly beneficial in pipeline situations prone to column separation. Its purpose is to close when exhaust rates are elevated and to govern the air valve's exhaust rate, preventing the water column from impacting the air valve forcefully, which could lead to water hammering or damage. The slow-closing device can be fixed to the inlet of potable water valves and the outlet of wastewater air valves during potential column separation or vacuum instabilities.

The combination air valve encompasses the functionalities of both air/vacuum and air release valves. It may be constructed in either a single-body design, integrating both functionalities in one unit, or a dual-body approach, where an air release valve is connected alongside an air/vacuum valve. Both configurations ultimately provide the same operational capacities, although the single-body design offers a cost advantage, whereas the dual-body layout allows for more flexibility in orifice sizing.

Strategic Locations for Air Valves Along Pipelines

Air valves are generally positioned within liquid piping systems to release air or gases while allowing for atmospheric air intake, thus preventing vacuum states and air-related surges. The AWWA Air Valve Manual advises placing air valves at various key locations, including high points, lengthy runs, adjacent to mainline valves, downstream from pumps, and where pipe inclines shift. Manufacturers often provide computer-based tools to assist in the accurate placement and sizing of air valves.

For optimal performance, installation methods for air valves hold significant importance. Typically, the best outcomes are achieved when air valves are mounted directly atop the pipe. However, when pipelines are situated beneath roadways, a separate vault may be necessary for the air valve. In these scenarios, it is critical that connecting pipes are appropriately sized to accommodate flow conditions and have an upward slope leading to the air valve. Moreover, extended air valve piping could exacerbate surge conditions, necessitating transient analysis for evaluation.

When conducting maintenance on air valves, it is advisable to include isolation valves underneath the valve installations. Additionally, to efficiently gather air traveling along a pipeline, a riser pipe that surpasses the air valve inlet size is recommended. Having a drain valve enables annual checks on air valve functionality. If air is released from the drain valve, maintenance or repairs may be required for the air release function. Otherwise, the air valve should be monitored during pump operations to confirm that it is exhausting air and securely closing without excessive leakage.

Special precautions are essential when inspecting or servicing an air valve, as they can release significant amounts of pressurized air or admit large volumes of air under vacuum conditions, posing potential risks. All maintenance endeavors necessitate the closure of the isolation valve beneath the air valve. However, even after closure, some pressurized air may still be contained within the valve. Caution should be exercised when venting the air through a drain valve or pipe plug prior to removing the air valve cover.

Conclusion on Air Valves in Piping Systems

Allowing air accumulation in pressurized pipelines can severely hinder efficiency and lead to detrimental damage to the system. By comprehending the different varieties of air valves available, system designers can make informed choices about selecting and installing air valves, thereby ensuring robust protection for liquid piping systems.

JOHN V. BALLUN, P.E. serves as the President and CEO of Val-Matic Valve & Mfg. Corp. (www.valmatic.com). He has contributed to the development of valve standards for the American Society of Safety Engineers, AWWA, and Manufacturers Standardization Society (MSS), and previously held the position of president at MSS.

Common Questions About Air Valves

• What are the benefits of using air release valves in piping systems?
  Air release valves help eliminate air pockets, thus maintaining optimal pressure within the pipeline, reducing energy costs, preventing water hammer, and minimizing system strain.
• How often should air valves in piping systems be maintained?
  Regular inspection is recommended at least once a year, with additional checks needed after significant system changes or repairs.
• Can air release valves be installed in any piping system?
  While air release valves are versatile, specific configurations and sizes should be matched to the unique characteristics and demands of each piping system.

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