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DIY VACUUM MANIFOLD
An Erik Ersland creation
This has been updated. It turns out brass is corroded by miniprep reagents. Do not use brass, only use plastic (preferable the same plastic for everything).
Midipreps require a vacuum manifold and minipreps may use it if you so choose. It uses vacuum to draw fluid through a spin column. Our labs manifold was in poor shape, the hose was attached with a quarter inch mass of parafilm and the opposite end from the hose leaked. A new 24 tube vacuum manifold from QIAGEN costs $270, the following kit cost 15.21(even with a lot of leftovers) and holds 36 tubes.
Tools
something to cut PVC pipe, I used a hacksaw and the wood saw on my multitool.
Something to tighten the brass fitting, I used a crescent wrench
optional: Hot glue gun or teflon tape to seal brass fitting, probably not needed
Parts
3/4" PVC pipe, the size of manifold you want determines amount. I used a 10 foot segment and probably have 4 or so feet left over. I had to cut this in half to fit it on the subway, if you have to use a train, make sure you are the type that always carries a saw.
3X 90 degree elbows, same size as pipe
3X Tees, same size as pipe
plastic barb to male thread adapter, sized for vacuum hose (I used 3/8 tube to 1/2" thread since its all I could find), the qiagen model appears to use 1/4 inch tube
PVC female thread to pipe slip, should fit into a tee socket and the brass fitting.
PVC cement
PVC primer (if you think you need it, the cement I have is rated to 180 PSI, and even at full vacuum, this is less than 15 PSI, I woldn't be surprised if hammering the joints together with a rubber mallet was a good enough seal)
note: You will have enough primer and cement to make 400 of these. You could probably get away with 1/2" pipe.
I bought some extras, you probably wont need any.
Layout
I ended up making a mistake and turning the brass hose fitting 90 degrees, I think the bellow configuration is probably better for our particular setup.
Assembly
I measured the depth of the fittings at 3/4". I doubled this and added 1/4" to get the small pieces for connecting the elbows and tees together. The saw eats up some amount of the material when you cut, so I like to measure-cut-measure-cut... to make sure the pieces are as long as I want them Try to get the cut nice and straight. If your cut isn't perfect, measure from the part that sticks out the most, that is the part that will bottom out when you put this together, all the imperfections at the pipe ends will be inside the fittings, only max length discrepancies will be visible. Remember to clean up the dust this makes and get all the mess off the ends of the pipe. It helps a lot to have the pipe secured when you cut it. You may want to try pressing these together, don't do it. The fittings are tapered and require a mallet to get in all the way, and are nearly impossible to get back out once together. (don't worry about when you cement them together, they go right in with the cement).
I then cut the long segments, 20 inches left 1 inch extra for the way I drilled 36 holes.
Next comes gluing. This must be done in a very well ventilated area, I'd suggest going outside. I didn't use primer, you may want to. Follow the instructions on the cement for actual technique. Remember to keep the positions of pieces correct when putting this together, and don't get them rotated wrong. I'd suggest putting the short pipes into the corner fittings, then the corners on the outer long pipes, then the tees on the inner long pipe, then then add the outside long pipe assemblies to the middle (this requires doing 2 joints at once, so be quick), and finally add the bushing reducer.
The brass fitting screws into the plastic threaded bushing. Pipe threads are tapered, they should get tighter as you screw them in. If the fitting doesn't get tight, it probably doesn't seal. Mine got harder to turn when the hex part you grab with the wrench ran into the plastic, do not mistake this for it getting tight.
You should use teflon tape to wrap the threads to make it fit tight, but I just used hot glue to seal around the fitting, this should work for a vacuum system.
Drilling the holes is the hard part. I considered lathing a piece with the correct taper and a flat on the top (where the end is shaped like an upper case T, where the vertical part is what forms the hole and the horizontal part flattens the pipe around the hole), then heating the pipe to make it moldable with a heat gun and pressing it into an undersized pilot hole. This is more likely to work, especially if you use a drill press and clamp the pipe to make sure its really straight. I just drilled the holes with a 5/32's drill and tilted the drill and rotated it around (at about a 30 degree angle). The tilt and rotate is better than using a larger drill bit, it makes the holes conical so the top is bigger than the tube and the bottom is smaller. This angle means that you are guaranteed to get the right diameter even with imprecise holes and imprecise tubes. It also allows the tube to get wedged in tighter and seal better. Try to keep the holes circular instead of oblong, it will make them seal better. Use a piece of scrap pipe to practice and test with a spin column. Also test with a spin column regularly as you drill the final piece. Remember that you do not have a magical drill that can redrill a hole smaller, so when in doubt, drill a hole small first then re-drill bigger. Also, the spin columns wear out when you put them into and take them out of holes, so a spin column you use a lot will fit tightly in a hole that's too small for a new spin column.
I leave how to plug the extra holes as an exercise to the readers. I'd suggest tape(electrical feels like it would work the best to me), you could probably find non porous plugs as well.
Differences from Qiagen
This manifold has 36 holes. This manifold drains fluid into the vacuum tube, the Qiagen manifold stores fluid in the manifold and you can drain it out a capped hole on one end (the cap that leaks on ours). This means that you must have the manifold hooked up to a waste flask that is designated for QIAGEN waste (remember that mini and midiprep waste makes chlorine gas when combined with bleach). This also uses a 3/8" inner diameter hose, I think the Qiagen manifold uses something like 1/4" ID, you can probably stretch sufficiently stretchy hose, I managed to force our Qiagen hose onto this and it seals well. When adding tubes or plugs, don't force the them in. The vacuum will pull things in as far as they need to be once all holes are occupied. Forcing things into the holes may stretch them out and make the fit looser. | 
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