The Problem with moisture intrusion After moisture or water vapor enters a sealed enclosure, it diffuses through the air inside, where it can later condense
Yes, but valves with a manual release button can also be opened manually to equalize pressure.
No, not unless you push the manual release button (only on those valves that have a manual release button). In automatic mode, they will equalize only to the level of the reseal pressure. That is, a TA333-05-05-R breather valve will only equalize to within 0.5 psid because below that the valve will be closed.
It depends. There are three common ways that liquid water can enter through a breather valve: submersion in water, directed streams of water (washdowns), and wind-driven rain.
For submersion, the valve will not open if the reseal pressure of the valve exceeds the hydrostatic pressure of the water plus any vacuum that has built up inside the container. For instance, at a water depth of one meter, the hydrostatic pressure is approximately 1.4 psi. Therefore, a valve with a reseal pressure of at least 1.5 psid will prevent water intrusion at a depth of one meter, subject to the following qualification. If the container has developed a vacuum due to a temperature change, or due to a pressure change from land or air transport, the valve could still inhale water. For example, a container with a vacuum of 0.5 psi that is submerged in water until its breather valve is one meter deep will need a valve with a reseal pressure of at least 2.0 psid, because it needs to withstand 0.5 psi vacuum plus 1.4 psi hydrostatic pressure.
Note that submerging a warm container in cold water will develop a vacuum inside the container. If your container is subject to this condition, contact an AGM engineer for assistance in calculating its effect on your container.
For a valve subjected to a washdown, the breather valve’s cover configuration and vacuum setting determines whether it is susceptible to water ingress. An AGM breather valve with a solid cover and a nominal cracking pressure in the vacuum direction (i.e., the inward flow direction) of at least 1.0 psid will repel water entry from a directed stream of water. AGM valves with a solid cover include the following: TA333-R, TA330, TA770-R, and TA225. On the other hand, valves without a solid cover, such as TA238-R, TA240-R, TA292-R, and TA294-R valves, as well as competitors’ valves with only a screen over the valve opening, could allow water from a directed stream of water to enter during a container washdown.
Finally, for the condition of wind-driven rain, an AGM breather valve with a solid cover will repel wind-driven rain even when the valve is inhaling. AGM’s unique cover design forces the airstream through two 180° turns, thereby causing most water droplets to fall out of the air stream. By contrast, a breather valve without a solid cover will repel wind-driven rain only when the valve is closed. This type of valve could allow rain to enter during the brief instances when the valve is inhaling.
Note that the passage of liquid water through a valve is only one of the two ways that moisture commonly enters a container. The more common way for moisture to enter a container is in the form of water vapor, which is entrained in the air that the valve inhales, and also permeates through a container’s seals. Contact an AGM engineer for assistance in determining how to protect your container’s contents against this type of water ingress.
No. AGM breather valves are small mechanical systems where a spring pushes a seal onto a seat. Due to the surface energy forces of the elastomeric seals, it will always require slightly more force to open the valve than to close it. Therefore, the opening pressure will be slightly higher than the reseal pressure. Also, the higher the setting of the valve, the greater the difference between the opening and closing pressures.
We have made valves with reseal pressures as high as 10 psid. However, these valves are difficult to work with and the settings may tend to shift after long periods of time and large temperature changes, but they will continue to perform their basic function.