An automatic air release valve provides a critical role in pressurized piping systems. In this blog post, we will discuss the best industries and applications for air release valves, their key advantages, and even some disadvantages.
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WHY AIR RELEASE VALVES?
Air trapped in a pipeline will naturally rise and collect at high points within the system. This trapped air can cause pump failures, faulty instrumentation readings, corrosion, flow issues, and water hammer or pressure surges. Unnecessary air in the pipeline also makes the pump work harder, resulting in additional energy consumption.
Oftentimes, the air in the pipelines is not due to improper installation of the pipes or supplemental equipment, but instead, a failure to properly de-aerate the line.
Air in the pipeline comes from 3 primary sources:
- The pipeline itself - Before start-up, a pipeline isn&#;t technically empty, it&#;s filled with air. Until the pipeline is filled with fluid, the air must be evacuated.
- Fluid pumped - Water contains 2% air by volume. Other fluids like adhesives, or other thick fluids, can trap air in pockets. As fluid moves through the system, air separates from the fluid and accumulates at system high points.
- Mechanical equipment - Air can be drawn into the system through equipment like pumps, packing, valves, and pipe joints.
As air accumulates at high points in the system, a line restriction occurs. This line restriction increases head loss and increases pumping cycles, therefore increasing energy consumption.
As the fluid is forced through the restricted pipe, its velocity increases. As the velocity increases, it&#;s possible that all or part of the air pocket will break away and be carried downstream. This causes a high-pressure surge or water hammer.
Pressure surges and water hammer can cause serious damage to pumps, valves, and pipes. This is the biggest consequence of allowing air to accumulate in system high points.
If the pocket of air is not carried away by the velocity of the fluid, the pocket of air will continue to grow and cause the system to become completely air bound, resulting in flow stoppage.
The purpose of air release valves is to continually release excess air out of the system, resulting in smooth and efficient operation.
HOW DO THEY WORK?
Automatic air release valves are installed at the highest points in a pipeline where air naturally collects. Air bubbles enter the valve and displace the liquid inside, lowering the liquid level. When the level drops to where it no longer buoys the float, the float drops. This motion pulls the seat away from the orifice, triggering the valve to open and vent the accumulated air into the atmosphere.
As the air is vented, liquid re-enters the valve, once again buoying the float, lifting it until the seat presses against the orifice, closing the valve. This cycle automatically repeats as often as necessary to maintain an air-free system.
Proper installation is critical to the operation of air release valves. Because these valves are designed to release air from the piping system, they should be placed where the air is most likely to collect. Install them at system high points in the vertical position with the inlet down. Remember to add a shut-off valve below the valve in the event servicing is required.
BEST APPLICATIONS FOR AIR RELEASE VALVES
Water pipelines and sewer force mains are popular areas to find air release valves. If correctly installed, you should see them at the peaks and high points of the system. Sometimes they might be slightly downstream or paired with a combination air/vacuum valve. Air release valves are ideal for any type of closed-loop or pressurized piping that can entrap air.
Air release valves have small orifices when compared with other types of air valves. Therefore, they&#;re best for applications with smaller volumes of air to exhaust.
ADVANTAGES
Air release valves protect the pipeline system and maintain its efficiency. These valves are perfect for quickly venting large volumes of air during filling or startup. They also allow air back into the pipeline during emptying. This is important because some pipe materials can collapse under negative pressure.
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Once an air release valve is installed, it constantly operates automatically.
DISADVANTAGES
If a pipeline is filled or emptied too quickly, an air release valve does not always keep up with the air flow demands. You must size the valve correctly for your application.
IN CONCLUSION
When air is allowed to accumulate in pumping systems, the risk for damage to mechanical equipment is heightened and efficiency is sacrificed. If a pumping system is experiencing pressure surges and lowered efficiency, implementing air release valves might be a good place to start.
Do you have a pipeline that might need an air release valve? Make sure you get the right valve for the job by talking to an experienced engineer.
If you need help selecting the right pump for your application, ask us about it! We gladly provide technical assistance to businesses in Wisconsin, Minnesota, Iowa, and Upper Michigan.
Liquid piping applications are vulnerable to air entering the system through connections, pumps and incoming fluids, causing inefficiencies and operating issues. Air release valves are designed to combat this issue and release pockets of accumulated air to maintain a consistent and safe system. However, they must be installed at optimal locations to expel the maximum amount of air early and make the application as efficient as possible. When installed correctly and at the optimal locations, air release valves allow for greater fluid flow and help to protect systems from the chance of pressure surges.
At John Valves, we manufacture and supply air release valves in various sizes to support the efficiencies in industrial fluid applications for clients around Australia. In this article, we discuss where to install air release valves as best practices for fluid systems.
Where to install air release valves
Air release valves are installed to expel air or gases when they&#;ve accumulated inside liquid applications as well as assisting in the prevention of pressure surges. They&#;re essential in ensuring that the system is operating efficiently to maintain a high flow performance through the pipeline.
Air can enter pipelines in various ways and locations and can travel with the fluid until it becomes trapped and accumulates. It&#;s these areas of accumulation where valves must release air to maintain an efficient system. When possible, install the air release valves directly on top of the pipe in a vertical position to have the best effect. Below we look at various locations along the pipeline where air pockets are likely to accumulate to help you determine where to install air release valves:
Bends or elbows
Bends or elbows are typical locations for air to become trapped, as air usually has a different density to the fluid, so it can become &#;trapped&#; when the flow reaches a turning point. Therefore, we recommend installing air release valves as close to bends or elbows as possible to expel air or gases from the system. When this isn&#;t possible, you can install a tee at these locations, which will allow the air to accumulate in the tee and then move into the air valve.
Downstream of pumps
Pumps involve multiple piping connections and pressure changes of the fluid, which can result in the presence of air in an application. Installing an air release valve downstream from pumps means that any air that enters the system at the pump can be expelled once it accumulates and reaches the air release valve. After shutdown, pump casings can also fill with air, so when the pump is restarted, this large amount of air is discharged from the pump and needs to be released before it enters check valves within the application. A specific type of air valve, called an air/vacuum valve, installed downstream of pumps is suitable for expelling this air.
High points, long runs and slope changes
As air and gases are almost always lighter than liquid, high points within fluid systems are prone to hold and trap pockets of air as it rises into these positions. Changes in pipe slope can also hold air pockets due to pressure and velocity changes. Both of these locations are suitable spots to install air release valves that expel this trapped air and enhance the system&#;s efficiency.
Air travelling within long horizontal pipeline runs can remain in the system for a long time without reaching a significant point to be released, making the pipeline over this length less efficient. It&#;s therefore a good idea to install air valves along long runs to expel pockets of air that may travel slowly and would otherwise affect the system for an extended period.
Adjacent to other valves
As an external connection point, valves are susceptible to allowing undesired air into the system. Installing air release valves adjacent to or downstream from mainline valves enables air that enters through valves to be expelled soon after it enters, minimising the inefficiencies caused.
Summary
The locations along pipelines mentioned in this article commonly contain air within applications and cause inefficiencies. While installing air release valves in these locations is recommended, it&#;s also important to be mindful of other areas where piping connections may allow air to enter and require an air release valve to exhaust the air. John Valves has helped many facilities operate fluid applications with sufficient, custom-made air release valves to suit their needs. If you need help in selecting an appropriate valve, please get in touch with our team.
