Pressure Equalisation Solutions

Pressure balance elements and pressure balance cable glands to prevent the formation of condensation in electronic and electrotechnical components.

Pressure Balance Elements (PBE) & Drain Plugs (DP)

Portfolio PBE + DP / Diversity

Condensation forms in enclosures due to temperature and pressure fluctuations caused by the environment, climate and the actual operation of the system. Excess air humidity condenses in the coldest places in the housing as condensation. pressure balance elements (PBE) and drain plugs reliably prevent the formation or accumulation of condensation water. Maintenance and repair costs for electronic and electrotechnical components are significantly reduced in this way. In addition to an extensive range of pressure balance elements made of plastic and stainless steel, combined with important approvals - including those relating to UV resistance or the possibility of use in potentially explosive areas - RST offers a wide range of application-specific solutions.

From..

a) mini versions in M8x1.0 or M6x0.75, which play an increasingly important role in times of smaller and smaller getting electronic and electrotechnical components,

b) via cable glands with an integrated pressure compensation function, which combine the properties of conventional cable glands with those of a pressure balance element in one product,

c) up to our new safety pressure balance elements, which primarily ensure pressure equalisation, but also act as a pressure relief valve in an emergency (mainly used in the field of Li-ion battery technology),

... we have the right solution for almost every challenge. And if the formation of condensation water cannot actually be avoided, a wide variety of drain plugs provide a remedy.

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:

1. Permanent air circulation into the enclosure

2. Cooling the enclosure

3. 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 use a DAE?

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 as high as IP 67. Thirdly, due to gas permeability a PBE prevents corrosion and water condensation inside the enclosure – in most cases.  

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 as this is responsible for the IP grade. 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.

With the same membrane type and the same active surface, an increase of AFR means a decrease of the WIP, which in turn influences the IP protection class. 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.

How does a PBE avoid water condensation?

PBEs use air permeable membranes which allow air (gases) to penetrate but block water, other fluids and dirt/dust. This way high protection classes like IP 64, IP 65, IP 67 and IP 69 can be realized even the system can breathe. When using a PBE it doesn’t make sense to go for IP 68 – as it won’t be possible for the system to breathe under water (either a snorkel is used).

As environmental air contains water vapour this gas can also penetrate through the membrane – on both directions as the membranes are bi-directional! In the case condense water already gathered inside the housing during cooling down or production process this condense water will be pumped out of it. Therefore several cycles of switch on/off will be necessary. At the end of the day the system will be in balance with the outside climate: humidity inside and outside will be identical. This process is depending on the temperature difference inside/outside: the higher this difference the faster the equilibrium is achieved. Assuming that the inside temperature will be always above (in worst case identical) the outside temperature no water condensation inside the housing will take place.

These general guidelines are important during the design of a system. A vent plug should be mounted on the upper side of an enclosure to prevent blockage of the membrane – whereas our vent glands can be used and considered as standard glands mountable wherever a cable has to be inserted. Additionally our vent-Calculator www.ventcalculator.com/de.htmlr is an excellent tool to find out which and how many PBE should be used for your application.

Diagram of pressure curve

When to use drain plugs?

As already mentioned in most cases a PBE can avoid water condensation inside a housing. But there are some situations where a drain plug is needed. This is depending on the mounting situation, operation conditions as well as of the environmental conditions.

Vapour condenses primarily at so called cold-traps – at the coldest sites of a system. This is because at that site the dew point is exceeded. Let’s consider a realistic situation: at an air temperature of 30°C the saturated water density is 30 g/m3 (= 30 mg/ltr. i.e. one litre air contains 30 mg water); a relative humidity of 70% means 21 mg/ltr; now we are looking for an air temperature, where 21 mg/ltr equals the saturated water density of 100%; at this temperature condensation will take place. In our calculation we will end up at about 19°C! At a relative humidity of 40% (12 mg/ltr) the dew point would be at about 11°C. To summarize:

30°C and 70% humidity: water will condense at 19°C; ΔT=11°C

30°C and 40% humidity: water will condense at 11°C; ΔT=19°C

This means cooling down a system from 30°C to 19°C respectively 11°C will cause water condensation! The higher the relative humidity the lower the temperature difference when condensation will occur. In other words: in high humidity and fast changing operation (temperature) conditions a drain plug will be the right choice.

Drain plugs are mounted at the lowest/deepest position of an enclosure/housing to allow water to escape by gravity.

Summary

In most cases PBEs avoid water condensation and therefore corrosion inside a housing. For some critical situations a drain plug will be the right choice. Sometimes we are asked whether a combination of PBE and drain plug can be used. As most our drain plugs are specified for IPx5 this could be an alternative – depending on the application.

In some specific cases neither PBE nor drain plug could solve the problem. Just keep in mind that both products are passive products; their functionality is depending on the environmental and operational situation. This means some applications need active air conditioning inside the housing; this cannot be realized by passive PBEs or drain plugs.