Choosing the right breather valve to protect your project is no simple task. When it comes to pressure differentials and their interaction with sealed spaces during flight, aerospace engineers must take into account several aspects of pressure and environment to ensure the safety and reliability of their aircraft, spacecraft, and equipment.
What are pressure differentials?
Pressure differentials are an inherent challenge in the aerospace industry. As an aircraft or spacecraft ascends to higher altitudes, the air pressure outside the vehicle decreases while the pressure inside remains constant. This is also the case for externally mounted equipment, such as aerial optics systems or electronics housings.
The difference in pressures is known as a pressure differential, and it can lead to problems such as leaks, material failure, and even structural damage, if not managed properly.
However, aerospace engineers need to understand both the rate of change and magnitude of pressure differentials that occur during flight to properly protect craft and equipment.
Breather Valves and the Rate of Change of Pressure Differentials
As an aircraft or spacecraft ascends, a pressure differential can develop quickly. If pressure is not equalized to safe levels fast enough, a differential in excess of a vehicle or enclosure’s pressure rating may develop. As a result, such excessive pressures can cause catastrophic failure of the vehicle or equipment.
As a point of emphasis, the rate of change is of special concern in comparison to the magnitude when specifying breather valves. This is because a breather valve, to be effective, will have to flow enough air at a fast enough rate to avoid the development of a magnitude greater than the given enclosure’s pressure rating.
Therefore, when reviewing breather valves, it’s very important to know the rate of change in pressure differential that the enclosure in question will experience.
Breather Valves and the Magnitude of Pressure Differentials
Nevertheless, the magnitude of a differential is important in determining an appropriate breather valve for a given situation.
First and foremost, it’s important to review the pressure/vacuum rating of a given enclosure, as this will provide the maximum differential allowable.
Once the maximum pressure differential has been determined, the flow capability of a given breather valve is evaluated at that maximum pressure. Doing so provides a determination as to whether the flow through the breather valve is sufficient to protect the enclosure.
Breather Valves: Managing Pressure Differentials During Flight, Altitude Change, or Temperature Cycling
Breather valves prevent damage through the equalization of pressures to safe operating levels.
To do so, a breather valve must sufficiently relieve pressures within a time interval that would otherwise see the development of a pressure differential greater than an enclosure’s pressure rating. For example, during a decompression event, a breather valve must be able to open quickly enough and to provide enough flow as to prevent damage, such as ruptured seals or deforming enclosure walls.
Rockets, planes, and spacecraft all ascend and descend very quickly. During their flight, the ascent and descent speeds may be great enough to generate differentials both in significant magnitude and rate that can easily cause damage to an enclosure and see a breather valve struggle to keep up if not appropriately planned.
For this reason, it’s very important to have a firm understanding of cracking and reseal pressures, how pressure differential rate and magnitude factor into a breather valve’s performance, and the difference between spring and magnet breather valves.
For more information about these and other aspects of breather valves, see AGM’s Knowledge Hub.
Types of Breather Valves
AGM carries mainly two types of breather valves used in aerospace applications: spring-actuated and magnetically-actuated valves. Both types of valves perform the same function of regulating pressure differentials, but they do so using different mechanisms. These variations in their functioning make each type of breather valve better suited to different situations.
Spring Breather Valves
Spring-actuated breather valves use a spring to regulate the valve opening.
A spring breather valve consists of a:
- Valve body,
- Spring; and,
- Disc or poppet that seals the valve.
As pressure increases above the set point of the valve, the spring compresses, causing the poppet to lift off its seal. This pressure level is known as cracking pressure and is the point where the valve opens to allow air to pass through.
As pressure further increases, the valve gradually opens with it, eventually reaching a maximum and allowing its greatest possible air flow to equalize the differential.
As the pressure differential is reduced to a safe level, the spring decompresses, causing the disc or poppet to return to its original position and the valve reseals.
Spring breather valves are simple, reliable, and low cost, but the gradual increase in air flow from cracking to full flow makes them less suited for situations in which a great deal of air must flow in a short period of time.
Magnet Breather Valves
Magnetically-actuated breather valves use the attractive force between two magnets to control the valve opening.
A magnet breather valve consists of a:
- Valve body,
- Retention spring; and,
- Magnet pair.
As pressure increases above the set point of the valve, one of the magnets is pushed back. Once the distance between the two magnets has increased beyond a certain point, the attractive force is not strong enough to hold them and the valve flies fully open to allow full-flow pressure relief almost instantaneously.
As the pressure differential is reduced to a safe level, the retention spring provides just enough force to push the magnet back into a distance with the other magnet wherein their attractive forces hold them closed.
Magnet valves provide greater air flow faster in comparison to most spring valves and can regulate a wider range of pressure differentials.
Choosing Breather Valves
When selecting between spring-actuated and magnetically-actuated valves, aerospace engineers must account for many performance factors, including:
- Pressure range
- Response time
…and much more! These factors can vary depending on the specific application and operating environment.
This process requires careful consideration and is often best done in collaboration with experienced professionals.
For more information about breather valves, see AGM’s Breather Valve Knowledge Hub.
For technical assistance in selecting a breather valve for your application, contact AGM.
Breather Valves for Aerospace vs Other Industries
It is worth noting that while the core technology and function of the breather valves discussed above are the same as those common to other industries – such as chemical storage – certain aspects may differ in important ways.
In the aerospace industry, breather valves are used to manage pressure and prevent damage to sensitive electronic components, ensure proper fuel flow, and control internal pressures, such as in the cabin of an aircraft. Frequently, they are also used on transport containers, cases and device enclosures shipped via truck, aircraft, or ocean vessel. These breather valves are designed to withstand the extreme temperatures, pressures, and environmental conditions that are frequently encountered during flight and shipping.
Conversely, breather valves used in an industry such as chemical storage, are primarily used to regulate pressure and prevent the buildup of hazardous gases in tanks. These valves help to maintain a safe environment for workers and prevent explosions or other accidents that can result from the buildup of pressure or flammable gases. Such breather valves are typically designed to withstand exposure to harsh chemicals, corrosive substances, and other hazardous materials.
Need a Breather Valve? Contact AGM
For help specifying an appropriate breather valve, contact AGM Engineering today at 520.881.2130, or email us here.