4 Mistakes To Avoid When Ventilating Dry Filter Spray Booths

Dry filter spray booths offer a simple and efficient solution for extracting fumes and overspray in industrial spray-painting environments.

Specially designed paper filters in the booth remove sticky paint droplets and chemical particles from the exhaust air, maintaining an even airflow and creating a safe and uncontaminated area for spraying.

In this post, we look at some of the ventilation mistakes to be avoided when installing this popular spray booth solution.

Mistake 1: The vent surface is smaller than the filter face

The extraction system in dry filter spray booths works in a cyclical way – drawing in air through the filter face and forcing the filtered air into the atmosphere through an external duct.

The air that is extracted is then replaced by air outside the booth to sustain a steady airflow through the booth.

Most factory floors, warehouses, or workshops that opt for a spray booth will typically have some form of ventilation (window/door/air conditioning) to keep the air flowing.

However, if you are installing your spray booth in an enclosed area, a general rule of thumb is to create a vent on the opposite side of the filters with a surface area that is at least the same as that of the filter face.  Speak to your spray booth supplier or see the UK government guidelines HSG258 for more details on ensuring a good ventilation design.  

Mistake 2: There is insufficient duct length for the exhaust

It must be ensured that all exhausted, filtered air is discharged to a safe place in the open air. As per Defra (Department of Environment, Food and Rural Affairs) stipulations on Industrial emissions, the exhaust pipe should be:

• At least 3 m above ground level
• At least 3 m from building openings, boundaries, sources of ignition; and
• Away from building eaves and other obstructions.

Mistake 3: Insufficient airflow speeds

The airflow velocity in a spray booth is the airspeed that is sufficient to pull polluted air away from the sprayer. This is typically measured at points around the article that is to be sprayed.

To ensure good extraction, the general recommendation is to maintain a minimum average air velocity of 0.7 m/s at the front of open-fronted booths and enclosures.

If the sprayer works inside a side-draught booth or enclosure, the minimum average air velocity where the sprayer stands should be at least 0.5 m/s with a minimum measured value of 0.4 m/s. In situations where a sprayer works inside a down-draught booth or enclosure, the recommended air velocity is an average of 0.4 m/s with a minimum measured value of 0.3 m/s.

It is advisable to leave the fan running for several minutes after spraying has finished removing vapours from the system effectively. This can be done with a time delay in the switching circuit of the fan motor.

However, remember never to leave wet items in a booth or enclosure when the ventilation is switched off, such as during lunch or tea breaks or at the end of the working day, as it can quickly create a flammable atmosphere.

Mistake 4: Failure to monitor filter health

Your spray booth is just as good as the condition of your filters.

Not only do soiled filters reduce the efficiency of extraction, but they can also be another fire hazard in the making.

If you are not doing it already, it is good practice to keep a logbook and do a manual check daily/weekly for paint build-up behind the filters. You can also use an airflow/air pressure differential switch or manometer – a simple inexpensive gadget that can provide a quick visual indication of when the filter needs changing.

The manometer is typically placed between the exhaust chamber and the painting area of the booth and measures the airflow resistance across the filters. Every time the booth filters clog up, the resistance measurement on the gauge will slowly increase, indicating it is time for the next filter change.

However, as the filters may carry toxic particles from the used paints, make sure you have full personal protection equipment, including goggles and air air-fed mask, if possible, when doing filter changes.

For more support and advice on spray booth installation, please feel free to contact our Masterflo spray booth team on 01753 59 59 55 or email us at sales@masterflo-uk.com.