Breather Valves (also known as Pressure Relief Valves)

How Do Breather Valves Work?

Breather valves automatically adjust the internal pressure of a sealed space with respect to the ambient pressure. This stops excessive differentials from damaging containers, housing, or enclosures.

Spring-actuated breather valves are common in most pressure mitigation systems. This type of breather valve is factory set at a specific cracking pressure (also known as an opening pressure) and will open once pressures reach that threshold. Spring breather valves operate via a poppet and spring method, whereby a spring at tension maintains the poppet in a closed position. Once the pressure reaches the cracking point, the spring tension is overcome, the poppet is pushed in, and the air is allowed to flow through the valve to relieve either pressure or vacuum.

Magnetically-actuated breather valves are most effective in circumstances involving pressure differentials of great magnitude with high rates of change, such as decompression events or when the rate of pressure change is too great for a spring breather valve to safely handle. Magnet breather valves function very similar to spring breather valves except that magnets are used in place of springs. The magnets enable these valves to fully open near instantaneously and provide a greater amount of air flow faster.

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. Under most conditions, pressure differentials are generated slowly and may be relieved with common spring breather valves. However, under some conditions, such as rapid ascent, descent, or rapid decompression, spring breather valves may not be enough. In such cases, ultra high flow breather valves, or magnet valves, can provide a great deal more air flow faster.

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.

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.

Breather Valves for Aero and Others

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.

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 Valves (Ultra-High Flow 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,
• Diaphragm,
• 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.

How to Choose the Right Breather Valve

Before making a definitive choice, you’ll need to know:

• How much pressure or vacuum your enclosure or container can withstand
• The internal air volume of your container or enclosure
• The expected rate of change of pressure
• The tolerance of the contents for moisture and particulate

To choose an appropriate breather valve, it’s important to understand that, fundamentally, a breather valve must perform two functions: Protect a container from excessive pressure or vacuum differentials, while limiting the amount of moisture that enters the container. Therefore, an ideal valve should remain sealed except during altitude change or under extreme temperature changes, but when open should provide sufficient flow to relieve air pressure as fast as it builds up.

It should be noted that breather valves set as low as +0.5 (pressure) and -0.5 (vacuum) psid will protect against excessive moisture intrusion for years.

Use our Breather Valve Selection Chart below for the flow rates of the various breather valves we carry.

When choosing between spring-actuated and magnetically-actuated valves, aerospace engineers must account for many performance factors, including:

• Pressure range
• Response time
• Accuracy
• Reliability

…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 technical assistance in selecting a breather valve for your application, contact AGM.

Specifications & Requirements

AGM breather valves are rigorously tested to ensure that they meet or exceed appropriate industry and government standards.

SAE Specification AS27166, entitled “Valve: Pressure Equalizing, Gaseous Products,” details environmental requirements and the procedures for vibration, temperature, salt, fog, sand and dust, rough handling, etc., as well as settings and flow. (Note: Many design activities have found it impractical to use the settings designated in this specification and have called out other settings more suitable for their particular container design.)

IMPORTANT: AGM Breather Valve Series TA238, TA240-R, TA330, TA333-R and TA770-R will meet all requirements of this specification (see Environmental Protection, above). AS27166 is also referenced in Department of Defense MIL-STD-648C.

Additionally, every AGM breather valve is individually tested and certified for compliance with performance requirements.

If you require identification of an AGM breather valve with a part number other than one shown on this website, please contact us for part number verification. Let us know if you also plan to put one of AGM’s catalog numbers on a document requiring MIL-STD-130 identification.

Mounting and Installation

Unless otherwise specified, all AGM breather valves are supplied with a nut, washer and gasket for

Unless otherwise specified, all AGM breather valves are supplied with a nut, washer and gasket for mounting through a hole on a flat, smooth surface. Valve gaskets may not provide a proper seal if the mounting surface is curved or rough. AGM breather valves can also be installed in a mounting flange or a threaded boss when a suitable counter bore has been provided for thread relief.

Additional Features

Some breather valves may come with or have the option to include:

• Manual release buttons: Push to release internal pressure or vacuum. This is especially desirable for containers with large lids or robust seals.
• Weather shielding: Weather shields help to prevent liquid water and debris from entering an enclosure when the breather valve inhales.
• Built-in humidity indication: Option for a humidity indicator card on the face of the valve. This enables quick visual inspection of the humidity level inside of an enclosure.