My interest in Mycology and Tissue culture started long back which led me to collect few laboratory equipment like Petri dishes, test tubes, weighing equipment, measuring glasses and also chemicals like Hydrogen Peroxide, Agar-agar and Potassium Permanganate. One equipment I wanted most but beyond my reach was a Laminar Flow Hood.
A Laminar Flow Hood provides a small sterile work area, where you can carry out all your culture works without the risk of contamination, simply by flowing completely purified air at a specified rate. However, the cost of the simplest form of the equipment is very prohibitive... the one with the very lowest specifications costs more than one thousand US Dollars... large corporations, universities, and research institutions can afford this but individual hobbyists like me can not.
The alternative...? Construct your own equipment...
There are two main types of Laminar Flow Hoods : Horizontal Airflow and Vertical Airflow. In a horizontal type, the purified air is blown from the back and moves towards the front of the working area. In a vertical type, the air is blown from the top over the working area and moves out through the base
I have carried out extensive study and came out with a design for constructing a Horizontal type Laminar Flow Hood, making use of a vacuum cleaner for the blower and press board / Plexiglas for the hood body thus reducing the cost considerably.
This Instructable will provide you step-by-step instructions on how to build your own portable Laminar Flow Hood without any compromise on standard specifications.
Step 1: Vacuum Cleaner as Blower for a Flow Hood...?
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Are Vacuum Cleaners Suitable for Laminar Flow Hoods as blowers...?
I have used Euroclean Star model vacuum cleaner to be used as blower in the flow hood. Let us check out the facts for its suitability for quality and effectiveness for being used in a flow hood.
The model I used consists of unique five stage filtration process and the air coming out after filtration is pure and fresh...
The first stage involves the incoming air to pass through a special particle, anti-microbial, biocide treated paper filter which has been treated for protection against bacteria, fungus and yeast. This paper bag is replaceable and can be used for up to five times. However, for better results, we can use fresh bag whenever we use the laminar flow hood. This air then passes through a cloth bag, which filters out any particle which escapes through the paper bag. This bag can be removed, cleaned and then placed again in position. The next three stages involve the air to pass through specially designed built-in electric filters with carbon which blows out completely pure fresh air.
I have removed the outer-most filter and provided a cheaper version of High Efficiency Particulate Air (HEPA) filter between the air chamber and the work area. I have also added a pre-filter to remove any heavier particles before the air is sucked into the vacuum cleaner.
Work area provided by the blower
Laminar flow hoods are designed to provide an air-flow of about 0.5 meters per second in the working area. The blower efficiency of the model I have used is 20 liters per second, that is 0.020 cubic meters per second including all filters. I have removed the outer most filter from the outlet for connecting the outlet pipe, and used the HEPA filter instead.
With 0.020 cubic meter of air per second, let us see how much work area it can cover
Air flow provided by the blower = width of HEPA filter x height of HEPA filter x air speed required
Work area (width x height) = air flow / air speed
= 0.020 / 0.50
= 0.04 square meter
Now, if we provide HEPA filter area of 0.27 meter width x 0.15 meter height, the available work area will be 0.04 square meters, which is sufficient for the effective functioning of the flow hood. I have provided the filter dimensions of 0.29 meters width by 0.15 meters height, considering the size of HEPA filter I could lay my hands on.
Advantages of using a Vacuum Cleaner as blower
There are some advantages in using vacuum cleaners, which may not be provided in a Laminar Flow Hood
I think a suitable vacuum cleaner will serve the purpose of blower in a small Laminar Flow Hood for hobbyists, thus reducing the cost as well as the weight of the flow hood considerably.
Step 2: High Efficiency Particulate Air (HEPA) Filter
I could lay my hands on a slightly larger sized HEPA filter used in window air conditioners. I have removed it from the original frame, reduced it to 29 centimeters by 15 centimeters size and mounted the filter to frame work made of Plexiglas.
This frame work is further fixed to the center of another frame of size 40 centimeters by 25 centimeters by cutting out the center portion to the required size. This frame is also made from Plexiglas. You can see the entire assembly of the HEPA filter in the first picture.
Plexiglas comes with protective covering on both sides to prevent any scratches.Do not remove these protecting covering while working with Plexiglas. I have used Gorilla Superglue for fixing and sealing the HEPA filter with the Plexiglas frame work.
Step 3: Materials Required
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The following materials are required other than the HEPA filter I have mentioned above for the construction
Step 4: Tools Required
Step 5: Constructing The Body With Press Board
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Constructing the main chamber with press board
I like to work in the open portico at my home. This place gives me enough space to work. It is also very easy to clean up the mess you create working with wood and other material
The assembling of the body with press board is complete. However, this is not airtight (will be done latter on). We will use Plexiglas for the top and front cover, which will give us a clear view while working in the flow hood.
Step 6: Plexiglas Body
As the main body is completed with press board, we can easily measure the top and front cover portions of the flow chamber. Cut the Plexiglas to the required sizes. Here, I have cut the top cover in to two pieces, one covering the air chamber and another for the work area. Do not fix them to the body... we will do it latter
Plexiglas comes with protective paper covering on both sides to prevent scratching the surface. Remove this covering only when you are satisfied that your work will not cause any damage to the Plexiglas surface.
Step 7: Fix Air Pipe and Finish the Body
The air inlet pipe needs to be fixed to the body of the chamber at the back. Cut a piece of air pipe being used in the vacuum cleaner. The top of the extension air pipe is slightly larger than the rest of the pipe as this will help in inserting the hose from the vacuum cleaner into the air pipe securely without any leakage. Make sure you use this portion of the air pipe for the air inlet.
As all our cutting and drilling works are completed on Plexiglas, we can safely remove the protective covering. Now our chamber can be taken inside the house for final assembly
Step 8: Fixing and Sealing HEPA Filter and Air Inlet Chamber
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Our complete assembly is inside home. See that the hose pipe from the vacuum cleaner snugly fits in to the air inlet pipe. Firstly, we will fix the HEPA filter assembly and the top back cover over the air chamber and check for any leakage.
Step 9: Test for Leakage and Airflow with Candle Flame
Allow the joints of the air chamber to cure for 24 hours before testing for the airflow and leakage
Step 10: Fixing and Sealing Top Front Cover
Now our Flow hood is ready. You can close the air inlet pipe with a lid when vacuum cleaner is not connected to the unit, thus keeping out dust from entering through the air inlet.
Step 11: Wiring
Not much wiring work is involved in our system. Vacuum cleaner has got its own electrical fittings and connections. We need to wire here for lighting with LED and UVC lamp through a two way toggle switch, which will allow any one of these to burn at any time.
Step 12: LED Lighting For The Work Chamber
Step 13: Add the UV Lamp
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A foreword on UV lamp before adding steps on installation
Ultraviolet lamp comes in different wavelengths. The lamp we use here has a very short wavelength of 280 - 100 nanometres (shortly called as nm) that uses ultraviolet light to kill microorganisms. This Ultraviolet rays are called as UVC (A and B have longer and medium wavelengths). This is known as Ultraviolet germicidal irradiation (UVGI). Using a UVGI device in a Laminar Flow Hood creates a deadly effect on micro-organisms and kills them all making a very sterile environment to work with. In a Laminar Flow Hood, redundancy in exposing micro-organisms to UV is achieved by circulating the air repeatedly which ensures multiple passes and will irradiate resistant micro-organisms more than once to break them down. Exposure to this rays are very dangerous, so take care while working with them.
Step 14: How To Use Your Laminar Flow Hood...?
How to use the finished Laminar Flow Hood...?
You need a clean room to place and work with the Laminar Flow Hood. Remove all unnecessary items and completely clean the room. Also take care that there is no open windows, doors or any free-flowing air in the room.
Step 15: Safety
Step 16: Conclusion
The total cost of the DIY Laminar flow hood worked out to 12000 Indian Rupees, (that is about 200 US Dollars) including the cost of Vacuum cleaner. If you already won a good quality vacuum cleaner, then you will have to spend about 4000 Rupees only for the other materials.
Please offer your comments and suggestions for any improvement in the above design.