How Breathers Work and How You Benefit
Installing a breather valve or waterproof breather vent (immersion breather) into the wall of a sealed cabinet or enclosure prevents pressure and vacuum differentials from developing. However, as simple as breather function may seem, breather operations and benefits are often misunderstood. Some common questions our customers ask about breathers are:

  • Are breathers designed to only allow moisture to leave the cabinet and not enter?
  • Is dry air allowed to enter?
  • Is there pressure required inside the cabinet for the breathers to allow any airflow?
  • Is it possible to calculate the airflow based on temperature or pressure rise?

AGM TA240 Design Drawing


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To help answer these questions, we’ll look at the operation of two common breather types: Pressure or vacuum-based resealing breather valves and waterproof breather vents, also known as immersion breathers. First, however, it’s important to note that each option discussed below has a different implication for moisture control. Therefore, it helps to think of pressure and moisture control as a system, rather than individual components. As a system, we’ll discuss installing breather valves in conjunction with desiccants.
Option 1: Breather Valves and How they work
Breather valves require a pressure differential to open and are closed except when breathing, so moisture ingress is limited to the moisture that is held in the air when the valve “inhales.” However, once moisture gets into your enclosure, the breather valve blocks it from exiting again, and you’ll need to use desiccant to adsorb this trapped moisture. The desiccant needs to be replaced at intervals with fresh desiccant. Using a breather valve with desiccant produces the driest environment possible.

Breather Valve TA240-R
AGM TA240-R Breather Valve

Option 2: Immersion breathers and how they work
Unlike breather valves, immersion breathers do not require any pressure to operate but still equalize pressure differentials. An immersion breather, also know as a waterproof breather, has a membrane that prevents dust and liquids from passing through, – making them great for protecting cases that end up submerged in water – but gases like air and water vapor will enter. However, water vapor will also pass back out through an immersion breather. In the event of rapid temperature drops when there is insufficient time for water vapor to exit through the breather, moisture inside the enclosure can condense.
While an immersion breather will not yield  as dry an environment as a breather valve with desiccant, it is maintenance free. Therefore, immersion breathers are commonly used in applications where occasional condensation will not cause a problem and where replacing desiccant is either not possible or desired.

TA248-1 Immersion Proof Breather
AGM TA248-1 Immersion Valve

A note on flow rate and steady temperature
When deciding to install either of the two above discussed breathers, knowing the flow rate of air through the breather given specific criteria, is often important. To calculate flow rate of air through a breather, one must know temperature change, air volume inside an enclosure, and the time over which temperature change occurs around the enclosure. At a steady temperature state, there will be no air flow in or out of the container, unless a pressure differential from another source is applied.




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