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soma_seeker posted a topic in MycologyHi everyone, I just wanted to share my design for a low-cost, small laminar flow hood. This hood was designed to aid in simple grain to grain transfer and agar work. I built this unit only several weeks ago, but I can report that after numerous attempts at both of these types of work, I have a ZERO contamination rate Prior to building this hood I was using a glove-box which was highly cumbersome, impractically small for grain to grain transfer work and still resulted in regular contamination when working with agar. Firstly, much of the credit for this work must go to Endorfinder for first alerting me to the fact that a home-made flow hood could in fact be prepared for less than the usual $400-500 price range. For those of you unfamiliar with the common design of a simple home-made hood, there are three key pieces; a pre-filter, a HEPA filter, and a fan. Endorfinder alerted me to a particular fan, which lowers the cost of the unit considerably but still provides the necessary function. This fan is available on eBay for $75 delivered. Generally, the fan is the most expensive of the three items, followed by the HEPA filter. In my (albeit limited) research, the cheapest HEPA filter I could find was approximately $100. This filter was an inch thick and filtered all material of a diameter greater than 0.5 micron. After scouring the net I then found this filter for $46. The dimensions of this unit (which is what gives you your effective working area), are 36cm by 27.5cm. It is sold as a replacement for a specific household air purifier, it is about an inch thick and is said to filter all material of a diameter greater than 0.3 micron. It should be noted that it is best to use a HEPA filter which is as deep as possible, so as to allow for a constant and steady outflow of air across the filter's surface. Using a one inch thick filter is therefore not ideal, but the goal of this design is to balance function with affordability (and as I have said, it has functioned very well for me so far). Also, the dimensions of this filter give a fairly small effective working area. I have found it to be sufficient, but i would not attempt anything smaller. For my pre-filter I purchased the pre-filter of the same model of air purifier. It cost me $11. I had intended to use this filter as is, but in the end I realised that it was far more appropriate to cut it to a smaller size. That being said, you might be able to find something cheaper that will do the job, maybe even something lying around the house (but this filter does do the job very well). The remaining items you will have to purchase are; 25mm wood screws (approx. $5), a combination glue/sealant (approx. $10) [NOTE: do not buy a simple silicone, buy a quality combination material that acts as both a glue and a sealant like this. Silicone will not do nearly as good a job in this application], 12mm thick plywood for the box (approx. $30 from Bunnings). So, you will require; - Fan $75 - HEPA filter $46 - Pre-filter $11 - Timber $30 - Glue/silicon $10 - Wood screws $5 Once you have obtained these items it is simply a matter of cutting your timber to size and assembling the components. For this you will require a power drill and a jigsaw (in order to cut a circular hole for the fan). I made the mistake of cutting my timber to size before my HEPA filter actually arrived. I used the quoted dimensions of the filter, which actually turned out to be a few mm larger than quoted. This resulted in the filter being slightly squashed in the frame (evident from the wavy pattern on the filter's surface). Obviously there is no need for you to make the same mistake. The (correct) dimensions of the pieces required (when using 12mm thick plywood) are; 2 x 30.2cm * 45cm (top and bottom) 2 x 27.6cm * 45cm (vertical sides) 1 x 36cm * 27.6cm (middle divider) 1 x 30.2cm * 38.6cm (back) Once cut to size, drill or jigsaw a hole in one of the sides at the bottom back position. This hole is for the power cord of the fan to exit. Place the cord through this hole and then, after applying a line of the glue/sealant along the join, screw the sides to the base. At this point I checked to verify the middle divider had been adequately cut to size, by placing it in position as shown in the photo below. Once I was confident that it was all flush, I traced around the diameter of the fan on the divider and cut this portion out using the jigsaw. I positioned the fan such that the small protrusion from the cylinder sat flush against the bottom of the box. This helps to hold the fan in position later. The following photo shows the positioning of the filter, divider and fan. Note that each of these three items have not yet been permanently fixed in position. The order this is performed in is important in order to properly seal the hood. The fan, divider and filter were then removed from position and, after applying a large line of glue/sealant along each edge of the HEPA filter, it was returned to its position (5mm back from flush with the edge of the plywood). Glue/sealant was then applied to the top of the vertical sides of the box and the lid was then screwed into place (optionally, you can attach a handle to the lid before screwing it into position). At this point it is now important to thoroughly ensure that all edges of the box are airtight. This is performed by applying the glue/sealant to each of the edges on the inside of the box (the outside is done as well, however it is important to do the inside while you still have full access to it). Pay particular attention to the edges between the HEPA filter and the box, if any air is allowed to pass through this area then the entire unit is compromised. Once you are confident that these seams are airtight you can put the divider in place, 17cm back from the end of the box. If you have prepared the box well it will likely be a snug fit and you might have to use a rubber mallet (or something similar) to knock it into place. Once in place you can drop a couple of screws threw the side to secure it, then seal the seams with the glue/sealant (however from now on the seam work is not as vital as it was when working with the HEPA filter compartment). You can now put the fan in place, such that it will rest flush against the back of the box, and apply the glue/sealant between the fan and what is likely a somewhat rough hole cutout. The cylindrical shape of the fan itself isn't perfect, so don't expect to have prepared a perfect hole into which the fan will fit snugly. Simply use a generous amount of the glue/sealant and it will be securely held in place. Now you can attach the pre-filter to the back of the box. To do so cut the pre-filter down to the shape shown in the image below. Then use the jigsaw to cut a rectangular whole in the back piece of the box which is around 1 inch shorter in length and breadth than the pre-filter. Attache the pre-filter using the glue/sealant, then attach the back of the box using a line of glue/sealant and screwing it into place. Now that the hood is fully assembled it is a good idea to go over all the seams of the box in order to seal any air-leaks, whilst focusing on the front portion of the hood. Pay particular attention to the seam between the HEPA filter and the box. The filter was installed 5mm back from the edge of the box, this was to ensure adequate space for a generous portion of glue/sealant, so as to ensure that no air whatsoever can escape from this space. Now that you have finished, allow the glue/sealant to dry overnight before turning the unit on. The next morning setup the hood on a desk in a room with no drafts/airflow and turn it on. Test the outflow of air by holding a lighter about 2 inches in front of the surface of the filter. The flame should bend very noticeably. As you move the flame around the surface of the filter it should remain bent and hopefully not vary much in its position (indicating a sufficient and constant outflow of air from the entire filter's surface). This hood (like all hoods) will work best in a room that is as small as possible. Before starting your work ensure that all surfaces have been sterilized with 60-70% alcohol, you have cleaned the airspace with an aerosol disinfectant such as Glen20, and that you have had the room sealed with the hood running for at least an hour in order to 'scrub' the air. Final note: Please bear in mind that this design is far from a professional laminar flow hood. The design has several key limitations that you should consider; 1. The HEPA filter removes material of diameter greater than 0.3 micron, however the general standard for mycology is a filter that removes anything larger than 0.03 micron. 2. The HEPA filter is quite shallow, which results in a less even and constant outflow of air from the entire filter surface. 3. The HEPA filter is fairly small, providing quite a limited working area. These points aside, this design is a low-cost and functional alternative to larger and significantly more expensive options. From the results I have obtained so far I think it is a highly effective tool for the recreational home mycologist. Ok you're done, go and prep some agar plates or try a grain to grain transfer