What is Air Valve and Why Do We Use Them?

Choosing the right location for the installation of an air valve is very important. To obtain maximum efficiency, the air valves are placed at strategic locations on the pipeline’s run. For proper aeration and ventilation of water and wastewater systems, air valves are required at the following points:

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Maximum High Points

Air bubbles accumulate and form air pockets that get stuck at the highest points in the system. Placing air valves here helps ventilate the air pockets out to the atmosphere.
Valve Required: Air release valve / combination valve.
 

Temporary High Points

Local high points can also serve as an accumulation spot for air bubbles. An air valve here vents the bubbles out to the atmosphere.
Valve Required: Air release valve/combination valve.
 

Long Rising or Falling Pipe Sections

Dislodged air pockets can flow downstream and form larger air pockets at the top section of the pipe. Also, rapid flow in downward sloping pipe sections can form a vacuum.  As a rule of thumb, air release valves and air vacuum valves should be installed every 800m on long pipe runs to properly vent and draw air into the system.

Long Rising or Falling Pipe Sections

Dislodged air pockets can flow downstream and form larger air pockets at the top section of the pipe. Also, rapid flow in downward sloping pipe sections can form a vacuum.  As a rule of thumb, air release valves and air vacuum valves should be installed every 800m on long pipe runs to properly vent and draw air into the system.
 

After Fast Closing Valves

When valves are suddenly shut off, vacuums can form downstream from the valve due to the momentum of the flow. For proper functioning of the pipe, the negative pressure needs to be relieved by admitting air into the pipe.
 

After Flow Throttling / Boosting Devices

After flow throttling devices like turbines or control valves, the pressure and velocity differences can lead to the formation of a vacuum. Air vacuum valves are needed close to these devices to draw air into the system Flow boosting devices like pumps and reduced pipe sections also draw air bubbles into the flow. Air release valves need to be installed after these devices to vent these air pockets.

Finally, always install your air valves at accessible, well-ventilated locations. This ensures they always have enough air to draw into the systems, and the air expelled has a route out. Also, it makes it easier to reach the valves for maintenance.

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All water supply systems consist of pipes that transmit water from its source to its destination. In this process, pockets of trapped air can form in the pipelines. Pockets of air and wastewater gases are difficult to detect and will reduce the overall efficiency of the piping system. The air pockets may also cause water hammer problems, full stoppage of flow, pipe bursts, system noise and pipe corrosion. Air in the pipeline can also cause unstable operation of control valves, meters and equipment. To secure a safe and efficient operation it is therefore critical to continually remove air and wastewater gases from the water system.

Why air appears in pipelines

Dissolved air exists in all fluid transmission systems. The principal sources are:

• Incomplete filling of the line which leaves air pockets at pipeline peaks 
• Dissolved air released from the fluid when pressure drops and/or temperature rises
• Air sucked into the system through openings at e.g. joints, breaks/bursts and accessories

If the volume of the air and wastewater gas pocket reaches a certain size, which especially occurs at pipeline peaks where air pockets naturally collect, a restriction of the flow occurs that produces unnecessary headloss risking complete stop of the water flow.

Why vacuum occurs in pipelines

Vacuum can occur in pipes due to lack of air in the system causing severe irreversible issues. Negative pressures left unmanaged have been proven to cause: 

• Damages of the pipeline causing suction of contaminants, mud and dirt through faulty connections, cracks in pipes and accessories
• Reduced lifetime of the pipeline due to positive and negative pressures acting on the pipe wall. This can result in fatigue loading which will weaken and eventually cause failure of the pipe wall. This is especially important on ageing pipelines where material degradation is likely
• In extreme cases even pipe collapse

Three issues must coexist for contaminant ingress to take place within water distribution systems:

1) The existence of a contaminant source external to the distribution pipe (e.g. contaminated ground water)
2) A pathway providing a route into the system (failing pipe joints or leaks)
3) A driving force (negative pressure within the pipeline)

One solution to prevent contamination is thus to remove one of the three issues: the driving force. Air valves are the most efficient and cost-effective tool to achieve this and by installing and maintaining a system with air valves, negative pressure is managed and removed from the equation, allowing even an ageing network to remain protected from contamination from the soil.

Vacuum in a pressurized pipe system can thus be caused by inefficient air valves not reacting to hydraulic conditions, air valves having failed due to lack of maintenance, and air valves being absent from the pipeline altogether.

Air valves are often associated with the release of air from the system, and therefore commonly known as air release valves. However, this name is misleading as their function of introducing air into the system to avoid vacuum is equally important.

The function of air valves

Air valves are hydromechanical devices with an internal float mechanism designed to release trapped air and wastewater gases during filling and operation of a piping system.

They also ensure air intake during draining to maintain a positive pressure. This is important as negative pressure causes vacuum that may result in pipe collapse and introduction of contaminants to the system.

Therefore, air valves provide protection from transient pressures and entrapped air in pipelines, which are the main causes of bursting, collapsing, and fracturing of pipelines.

With correct use of air valves, you will achieve:

• Reduced energy consumption and operation costs
• Reduced pressure loss 
• Reduced delays when filling the pipe system
• Reduced risk of water hammer
• Reduced failure or inaccuracies in flow metering
• Reduced corrosion
• Reduced risk of contamination
• Reduced risk of pipe burst and collapse
• Reduced costs for replacement
• Reduced depreciation due to increased network lifespan
• reduced required pump capacity due to lower head loss

Three main types of air valves

There are three types of air valves installed in water systems: automatic air valves, air and vacuum valves and combination air valves. 

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• Automatic air valves continuously release relatively small volumes of air from a pressurized line. Automatic air valves are also known as small orifice air valves and pressure air valves.

• Air and vacuum valves discharge large volumes of air when filling a pipeline. Air and vacuum valves make it possible to admit large volumes of air when lines are drained or when the pressure suddenly drops below atmospheric pressure. Air and vacuum valves are also known as kinetic air valves, large orifice air valves, vacuum breakers, low pressure air valves, air relief valves and single acting air valves.