BASICS ABOUT PRESSURE BALANCE ELEMENTS (PBEs)
When we refer to “Ventilation Plugs” or “Vent Glands” we should keep in mind that we are talking about “Pressure Balance Elements (PBEs)” because the main function of a PBE is to balance the pressure between inside and outside of an enclosure. In other words, a PBE is used to maintain a differential pressure of ΔP = 0 between inner and outer atmosphere of a housing.
It is important to notice that a PBE does not provide the following effects:
- Permanent air circulation into the enclosure
- Cooling the enclosure
- Dehydration of enclosed air
The maximum temperature of an enclosure depends on
a) The environmental conditions
b) The power dissipation of the (electronic) components inside
c) The design of the enclosure
d) The design of the heat sink
Consequently a PBE can only help to achieve a balance based on parameters a) to d) as quickly as possible. Reducing the maximum temperature of the system can only be done by improving the heat sinks or by forced cooling (active cooling systems like fans or Peltier elements).
Why to use a PBE?
First, it balances the pressure difference between inside and outside of an enclosure and eases the strain on enclosure seals and gaskets thus extending the lifetime of the complete system. Secondly, despite of being permeable for gases the protection rate will be IP 67. Thirdly, due to gas permeability a PBE prevents corrosion and water condensation inside the enclosure.
How to use a PBE?
There are two parameters, which define the performance of a PBE:
- Air Flow Rate (AFR)
- Water Intrusion Pressure (WIP)
Both parameters depend on each other and are functions of the used membrane as well as of the design of the PBE. A PBE should show a high AFR and the highest possible WIP. Generally, the AFR is determined at a differential pressure of ΔP=70 mbar (hPa). This is equal to ΔP=70 mbar=1 PSI (pounds per square inch; 1 Pa= 1 N/m2). Because most data are based on a differential pressure of ΔP=70 mbar it is possible to compare different PBEs.
An increase of the AFR means at the same time decreasing the WIP – when using the same PBE type. That is the Water Intrusion Pressure is lower for membranes showing higher Air Flow Rates. As a result, the Water Intrusion Pressure limits the IP rate of an enclosure when a PBE is used.
This fact is to be taken into account during the design of a system: the differential pressure ΔP should not exceed the WIP value – at least not during the cooling down process (after switching off the system) – as water could be sucked into the housing together with the air outside.
These general guidelines are important during the development of a system. Our PBE-Calculator is an excellent tool to find out which PBE and how many should be used for your application. Please contact our specialist for technical details at vent@. bimedteknik.de