Pressure Relief Valve for Cyclone Dust Extractor (Parametric)

prusaprinters

Paired with a cheap ebay cyclone dust extractor and a 30 litre bucket, my little Kaercher WD2 vacuum handles the sawdust and chips from my power tools handily. But I found that when I was using it for cleaning up, if I was careless about letting the nozzle get blocked, the suction would instantly crush the bucket. The solution is this little three-piece pressure relief valve.Drill a hole through the lid of the bucket using a hole saw (the STLs are sized for a 32mm hole saw, but the scad file is parametric so you can resize it to fit your hole saw). Clean the edge up with a sharp knife, then push the part pressurerelief_outer.stl through the hole - should be a nice loose fit. Mark the screwholes (on the flanges either side) on the bucket, then remove the part, drill the holes (I used a 4mm bit). Now assemble pressurerelief_outer.stl (outside of bucket lid) and pressurerelief_inner.stl (inside of bucket lid) and bolt together. I used short M4 bolts, but you can resize using the scad file if you want to use something bigger. I slathered pressurerelief_inner.stl with silicone sealant but this probably isn't necessary. Next, I glued a disc of 3mm neoprene to the top surface of pressurerelief_closer.stl. It may work just fine without this, but I wanted a nice seal with minimal whistling. I drilled through the neoprene to clear the central hole. Now, run a hex-bolt head M4x40 machine screw (or edit the scad file to use a larger size) up through the bottom of pressurerelief_closer.stl, so that the hex head is capture in the socket on the underside of pressurerelief_closer.stl. This part will be inside the bucket. Next, run the end of the bolt vertically up through the centre parts pressurerelief_inner.stl and pressurerelief_outer.stl. On the outside, drop an M4 washer over the bolt, then a spring, then another washer, and then screw a nut on. A 5.5x17mm compression spring I had on hand worked fine, but almost any small spring might do - say the kind you get with a Parker ballpoint refill? By tightening down the nut on the spring, you increase the pressure required before the valve will open; loosening means it opens sooner. Adjust to suit your vacuum and bucket.I ground the threads off the bolt where it passes through the plastic parts to help it move more freely. This may not be necessary - there's a bit of clearance in the shaft. If it's ‘sticking’, either grind the threads or maybe paint them smooth with nail varnish.Printing is straightfoward in the orientation of the STLs - no supports required. Infill shouldn't be too big a deal, but you probably want 3-5 shells/walls for it to work well and last. I printed in PLA and it works fine.Here's a wee video of the thing in action: