Dynamic elaboration on the Art & Science of Hazardous Area Protection
Condensation is a natural process by which the physical state of the matter is changed from GASEOUS STATE into LIQUID STATE. This process is opposite to that of VAPORIZATION.
In this article the CONDENSATION OF WATER inside the enclosure of light-fixtures,having protection of Increased Safety (Ex e) type is being analysed.
We will consider a Fluorescent Light Fixture , installed outdoors in the open . A definite volume of air is trapped inside the enclosure once it is installed and is ready for operation.
It is a natural phenomenon that condensation, in form of water vapors or small droplets, is deposited on the outside of the fixture, thus wetting the fixture and its seals .
During the operation of the light fixture, temperature rises, resulting in the expansion of the inside-air. The air expands and a small portion, forces its way out .
When the fixture is switched-off, it cools and causes an under pressure inside the enclosure, thus forcing the out-side air to enter inside.
The air from outside which enters have a relatively high moisture content and by virtue of CAPILLARY-LIKE natural actions the air & moisture is thus drawn in.
With any reduction of temperature the water vapors start forming small droplets of water ( Saturated air) , which are deposited on the components inside the enclosure.
The next operation of the light fixture (switching-on) will cause some air, from inside, to leak out. BUT this air has a LOWER moisture content than the air which was previously drawn in, because the deposited condensed water is left behind, in the component cavities.
Thus, with each heating & cooling cycle the quantity of deposited water increases.
DETAILS of the process
A small device , specially designed with built-in cavities and labyrinths , to let the enclosure BREATH, so that the pressure inside the enclosure is always equal to the pressure outside of the enclosure thus these is no condensation of water inside the enclosure and at the same time the integrity of the IP rating of the Ex e enclosure is not disturbed .
The most convenient way to install a breather is to design it as a gland and install it in any spare cable-entry opening.
Thus we have the BREATHER GLAND
If it is installed at the bottom of the enclosure (the lowest point in the enclosure , for that matter), the collected water can drain away without any hindrance.
The constructional of the Breather & Drain Gland (For Ex e Enclosures):
Material : Polyamide.
Working: The ventilating & draining properties are achieved through a combination of cavities & labyrinths.
(Ref: R.Stahl 8162 )
The use of the Breather & Drain Gland is recommended in the following cases:
1. Extreme ambient conditions of high humidity
2. Large fluctuations of daily temperature
3. High steam contents in the air
4. Frequent or intermittent operation