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.
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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.
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:
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.
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.
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.
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.
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.
There are three main designs to choose from:
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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 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.
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.
When modeling an air valve, it must conform to one of the four available types: (selected from the "Air Valve Type" attribute) Double Acting, Triple Acting, Vacuum Breaker and Slow Closing. Industry terminology is sometimes not consistent with HAMMER's definition of these types, so it is important to understand their behavior and assumptions. Below describes each air valve type and when it should be used.
Double Acting - This type of air valve has two actions:
The diameters of these orifices don't change during the transient simulation. This type of air valve should be used when air enters the valve through a specific size opening, and leaves the system through another specific size opening, without any transition. The opening that allows air outflow is typically smaller, in order to control air release. Here are some examples of when the Double Acting air valve type would be used:
Triple Acting - This type of air valve has three actions:
Air inflow passes through an opening with a fixed size. Air outflow first passes through a large-sized opening, which switches to a smaller sized opening just before all of the air has escaped. This cushions the air pocket collapse and subsequent collision of the water columns. This type of air valve should be used when the opening through which air is expelled changes based on some condition. The condition to trigger the reduction in size of the outflow orifice can either be based on a pressure differential or an air volume. Typically a float is used to decrease the opening size, but not always.
Here are some examples of when the Triple Acting air valve type would be used:
Vacuum Breaker - This type of air valve has only one operation: air inflow. During subatmospheric pressure, air enters through the air inflow orifice diameter. The outflow orifice diameter is assumed to be very small (effectively zero) so it doesn't let air out. When looking at the detailed report, you may notice the air volume change as the air pocket is compressed, but the mass of air in the pipe doesn't reduce. There are probably a limited number of applications for this type valve, but it may be used for a draining pipeline.
Slow Closing - This type of air valve has two actions:
Although similar to the other air valve types, the slow-closing air valve only has a single orifice involved; for the expulsion of air and liquid. An air inflow orifice is not required because HAMMER assumes that air will be freely allowed into the system (no throttling) when the head drops below the air valve elevation. The valve starts to close linearly with respect to area only when air begins to exit from the pipeline (after the head begins to rise).
It is possible for liquid to be discharged through this valve for a period after the air has been expelled, unlike the other air valve types, which closes when all the air has been evacuated from the pipeline. Typically you will want the valve to be fully closed after all air has been expelled, but before too much water has been expelled.
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