Choosing the Right Size of Air Valve

Choosing the right size of air valve is important and there are some important factors to be aware of. In fact, choosing the wrong size valve can defeat the purpose of the air valve entirely.

What are Air Valves

Air valves are mechanical hydraulic valves designed to automatically release. Or allow air in during the filling or draining of a piping system. Air is released from the solution in a pipeline due to areas of low pressure created by partially open valves. The differences in flow velocity, and changes in the elevation of the piping system. The air pockets that collect at high points in the system will reduce the flow of water in the pipeline by reducing the flow area and in severe cases, completely occlude the pipeline and stop the flow of water. Air pockets in pipelines are difficult to detect and will reduce the overall efficiency of the piping system due to the additional pressure loss and increased energy consumption required to pump the water.

Reasons for Gas or Air in Piping Systems

Air valves are designed to draw gas and remove it (de-air) from fluid management systems, such as sewage, drinking water, and irrigation pipes.

This protects the pipes and the entire system from damage caused by high pressures or vacuums created by accumulated air pockets. Gas can be introduced into the system in several ways:

• Naturally dissolved from water and wastewater
• During routine maintenance
• Left from initial installation
• Pulled into the system through other equipment (e.g., disturbances from pumps and other components)

If left unmanaged, the flow rate of fluid through the pipes becomes unreliable – structural damage and reduced flow rate lead to increased operating costs due to additional maintenance needs and operational inefficiencies.

When to Carefully Size Your Air Valve

Sizing your air valves correctly is an important factor to consider when installing a new system or repairing an old one. Doing a little background research into your operation and following some simple equations can help alleviate future headaches and potential disasters that can result from using the wrong size or type of air/vacuum valves.

What is the function of an air valve

Air/vacuum valves, also known as large orifice valves, are automatically float-operated valves that have two overall functions. The float-operated valve controls the release of air during piping system filling and will simply close when all air is exhausted. The valve will also open fully during draining or in the event of negative pressure. When sizing this valve, consider both filling and draining the piping system separately. As explained in more detail in this article.

Read more about: Air Valves Function

One important consideration in sizing a valve is that this type of valve will not release accumulated air from the piping system while the system is running and under pressure. An air/vacuum valve is typically equipped with a simple, double-way, float-operated valve seat that is normally open during vacuum piping conditions and fully closed during pressurized system operating conditions.

Sizing Factors for Choosing the Right Air Valve

The first step in sizing is to determine your maximum flow rate in gallons per minute (gpm) in the pipeline.

This may be a known constant for your particular system, or if it is gravity based. You may need to calculate it using the diameter and slope of the pipe. Once this is understood, it can be used to determine the rate at which air will be released in cubic feet per minute (cfm) when the piping system is filled. Using the gallons per minute flow rate, divide this value by 7.48 gallons per cubic foot to give you the cfm of air released.

Importance of Air Release Valves

The air release valve is the workhorse of air and vacuum valves, allowing air to automatically escape from the high points of the system at all times under pressure while the system is running. Clean water can typically contain about 2% air, while wastewater contains about 6%. Air is compressible in a piping system while water is not, and as a result of pressure changes in the system, it will come out of solution.

Air builds up at the high point of a piping system, causing a higher flow restriction, which increases operating costs. Also, if air is not properly vented from the piping system, you may have water hammer, higher pipe wear and maintenance costs.

Air relief valves are also referred to as small orifice valves due to the smaller orifice size compared to air/vacuum valves. They are usually connected with a hinged float mechanism as opposed to a simple float seat operation in air/vacuum valves. This is how pressure relief valves get their hydraulic-mechanical advantage of opening/closing and venting air under pressurized system operation.

Sizing an air relief valve can be a difficult task without a little basic knowledge and experience. That’s what CareWater experts are here to provide to their clients just contact us.

Selecting an Air Valve

There are three main designs to choose from:

• Single-function small orifice air valve (single-function/air release valve) – releases gas that builds up during operation.
• Single-function large orifice air valve (double-function/air release valve) – releases and admits gas during both the system drain and fluid compression (charging) phases.
• Double-port air valve (three-way air valve/combination valve) – has a small and large orifice for different gas inlet and outlet rates.

The size and material of the air valve is also important, to ensure that it can inlet/outlet a large enough volume to maintain the desired flow rate and withstand prolonged exposure to certain fluids (such as corrosives).

Read more about: Main Types of Air Valves

Combination Air/Vacuum Valves

Combination air/vacuum valves are simply an economical and practical combination of air/vacuum valves and an air release valve in a single body configuration. Typically, these combination air valves are available in smaller sizes, from 1/2 to 3 inches. In larger sizes, the larger air/vacuum valve may be equipped with a smaller air release valve on the side of the larger air/vacuum valve body. Sizing these combination valves generally follows the same steps as described above.

Important Precautions to Know

• A combination air valve, regardless of type, should be installed as close to the pipe as possible with an isolation valve.
• Isolation valves should be fully vented and connected to the top of the pipeline for ease of maintenance.

A good preventive maintenance schedule is also very important for all air and vacuum valves. As they are often located throughout the piping system in difficult to reach locations. This is often overlooked and misunderstood even after the valves have failed in service. You will find that when air and vacuum valves are properly sized and maintained. They will make your piping system more efficient with less maintenance.

When it comes time to install or replace air pressure relief valves and air and vacuum valves. Be sure to consider these factors and, when in doubt, call a valve professional. Experience and expertise go a long way in getting the right size valve for your specific application.