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Helpful information about waterproof membrane vents!

What is the function of a membrane vent?
Venting is essential to enable the proper functioning of high end technical electronic devices as well as basic every day products.  Vents allow pressure to escape, they protect electronics from contaminants entering the product, they aid cooling, help prevent condensation, all of these features helps the correct functioning of your device, maintaining its lifespan.

Typically your product is fully sealed, the gaskets all working and when closed nothing gets in or out.  This is where the vent is required.  Placing a hole in your product then placing one of our adhesive vent patches over that hole keeps the product waterproof and prevents dust and any other contaminants entering.  The size of the hole and the number of vents depends on a number of issues.  We can assist you to select the best membrane vent material for your device/application.

The membrane vent’s main function is to allow pressure to pass through.  In a sealed device, as sunlight hits the device or as the temperature rises, so does the pressure inside the box.  This pressure has to escape otherwise constant stress is placed on your product’s seals/gaskets. Conversely as the temperature reduces, so does the pressure, without a vent, the sealed box/device will attempt to suck the outside world into your device.  Through time this will damage the product’s seals and potentially create a point of failure for ingress to occur.

Any moisture that builds up within the sealed device as a result of condensation, could affect your product’s electronics.  A vent allows that moisture to escape, preventing condensation from forming.  This is why is is rare to see condensation in a vehicle headlamp these days unlike the past - as they are all now vented.  The moisture can now escape.

Devices with batteries require vents to deal with gassing, to maintain a safe performance of the device.


Automotive applications
Vents are used all over a vehicle, most obviously in the vehicle’s lights.  Without a vent pressure builds up and eventually its seals will fail.  Condensation is created due to the constant change in temperature – a vented light unit allows that condensation to escape.  Vents are used in areas such as the engine ECU, battery compartments, advanced electronics, on numerous sensors, car seats, actuator vents, fluid system caps, the list is long.

Without a quality vent your headlamp would very soon mist up – due to condensation, a vented headlamp or signal lamp will not.  Typically vents used in Automotive application use a silicon adhesive as it can be used in much higher temperature environments than vents using acrylic adhesive.


Protection of outdoor electronics
Weather creates a number of issues for a sealed device. Engineers will develop a robust box to withstand what the world throws at it, sunlight hitting the unit and massively increasing the pressure within, rain & sand blasting the device, if the product is vented, the pressure is equalised and your device will not attempt to suck in the rain/dust sitting on the outer walls.  As a device is moved from one environment to another, temperatures can change, for example, moving a truck from a refrigerated cold store, back out to the outside world – this creates a rapid change in temperature and all the associated problems that go with that.


Acoustic vents
Our range of acoustic vents allow for high quality sound to be achieved on a sealed product.  Whether it is a simple beeping/buzzer on your device used in a dirty environment, or the need for voice communications – maybe a handheld radio, or recording device.  At Selectronix Onboard Ltd our acoustic vents prevent dirt/dust/water from entering your product, yet achieving a high quality audio sound with minimal dB loss.  Our vents come in standard sizes, typically round patches, but often for acoustic applications a custom shape vent is needed.  No problem - just speak to us.


Information about installing and positioning a vent
An adhesive patch vent’s function is to allow airflow, to allow pressure to equalise with the outside world. It can also deal with condensation build up. The vent should be installed in areas where condensation is known to be a problem, or specifically closer to a heat source.  The vent should be positioned where water or debris will not sit on the membrane itself, creating a ‘pool’ or 'well' effect. Instead the vent should be placed where any water droplets can drain away immediately. So the underside of a product or a vertical wall is best.  The surface area where the vent will be installed should be smooth, even slight ridges or uneven paint finishes can create valleys where the adhesive may not fully adhere to the surface. For small volume applications and vent can be installed by hand.  The surface should be treated with alcohol to ensure any contaminants or grease is cleaned away.  The vent once position should be pressed down evenly with a gloved hand on only the adhesive area, trying to avoid the central breathing area. A finger should press here two to three times around.  Once positioned the vent should be left for 24 hours for the adhesive to fully cure before subjecting it to tests.  Don’t be tempted to pick at the vent to see if it has stuck to the surface!
It is also at this point worth noting that vents have a shelf life.  They can only retain their adhesive strength for a given period.  The vents will last longer if they are stored correctly.  That is; keeping them out of direct sunlight, keeping them in a sealed container at an ambient room temperature. Check with us for more detail about the particular vent that interests you.

In some instances it might be wise to make a small recess on your device wall to aid the installation of the vent, however, for smaller volume users this might restrict the exact size of vent you can use.  If your recess for example is 9mm and you normally use an 8mm OD vent, if there is no stock of the 8mm vent you won’t be able to use any larger sized vents if you had a sudden surge in demand.


How many vents do I need?
This is a very common question and there is no simple answer. Selectronix Onboard Ltd will help talk you through this process, discussing the purpose of the vent, the environment it will be used in.  The cubic volume and temperature change are the main focus point.  We need to allow for sufficient airflow over a given period of time for the vent to equalise the pressure. For example, if the vent was being used on a fighter jet going up into the sky, the change in pressure will be rather rapid!  It may be that a number of vents are required on a product, with varying levels of waterproof protection. We will talk to you about how to ensure the membrane vent is protected.  We can help with calculations of cubic area and temperature change in your device, look at the surface area through which you will be venting and thus what size of vent you require as we know the airflow rate of that material. The team at Selectronix Onboard are here to assist you - use us!


Which adhesive should I use?
There are basically two main types of adhesive used on vents – Acrylic or Silicon based.
Acrylic is more common, used for general applications. A vent only requires a very small surface area of adhesive to adhere to your device.  Even acrylic adhesive are incredibly strong. Silicon adhesives tend to be used in high temperature environments (100Deg +), or if a high peel strength is required, if the surface area where the vent will be installed is not flat but instead has a slight curve, then a higher strength adhesive might be required to ensure a strong bond is achieved.  Silicon adhesive is often the default type for automotive applications. If the area is not completely smooth, there are things we can do to ensure a reliable bond is made, like enlarging the adhesive area or manufacturing a custom extra thick adhesive layer.  Talk to us! +44 (0) 118 9817387


M12 and M6 Plastic or Metal Vents
In some instances a greater level of protection is required and you may decide to install a screw in M12 vent, or perhaps a 'push-fit' vent.  It maybe you prefer to make this item serviceable, so it can be swapped out over a given period of time due to the extreme environment of your application.  In these instance and many other, a plastic screw in vent is common.  They are available with varying membrane types - with differing airflow rates.  Speak to the team at Selectronix Onboard Ltd about the choices of external vent you have.

Created July 2019 by Selectronix Onboard Ltd
+44 (0) 118 9817387