Thread: My 3hp Dust Extractor

You can make a manometer to measure differences.

It can be cheaply made with clear plastic pipe mounted on a board and filled to a point with coloured water (I use red food colouring). I use a 30 degree angle. Lower the angle and make it longer to increase sensitivity.

The basic idea is the plastic tubing is inserted in the path of the suction, or at the end of the blower before the bag (via a hole), which measures either the vacuum or pressure.

When you were a kid you probably blew across a straw that was in your drink and noticed the fluid rose in the straw. Same principle. it's just a matter of marking what your "normal" is and trying to improve on it as you fiddle. There is no ready means of knowing what the actual pressure is without a purchased gauge...

If the pipe is inserted after the Blower and before the bag, one can use it to determine when the bags need cleaning. An increase in pressure means it is clagged. I do this for the pleated filter. It works really well. When it reaches my "bad" mark, it's time to twizzle the cleaning paddles.

You can use this $2 scale to do real testing on your pipes, lengths and bends. You can see the drop in suction visually as you add cruft onto the system.

Hope this gives you some ideas

If you google manometers or search the forum you'll see what I mean. It's a very low tech solution and it does look pretty cool

Originally Posted by Colin62

This is the inlet, with the 160mm coupling on it. You can see the grate and reduction in diameter, which drops the area from a nominal 200 square cm down to 102 square cm. That will need an angle grinder to open it up to the full diameter. The outlet is 150mmx120mm, with an area of 180 square cm (and rectangular), so I suspect that will become the limiting factor once I open up the inlet.

The first thing I would do is remove the grate as this restricts the air flow substantially more than it reduces the cross sectional are

The couplings. The bends aren't ideal, basically being angled, and it took me a few hours to smooth over the joints on the inside, where they were very jagged and had large overlaps. They're all 160mm stormwater piping and what they lack in sophistication, they make up for by being the cheapest I could get. I may start to replace them if the sharpness of the corners is an issue, but I suspect with 160mm pipe all the way through, that the inlet on the extractor is the main limiting factor here.

You can use a manometer to check this effect. To test how significant the these bends I would measure the the dynamic pressure of a bate length of duct and then joint as many of these connections together as possible and add these onto the end of the pipe and remeasure the dynamic pressure.

The coupling I plan to use as a bell mouth to suck dust from the lathe.
IMG_1091.jpg

While it will be slightly better than the naked end of a pipe unless the end has a significantly rounded lip it is not a bell mouth hood. The radius of curvature of the rounded lip should be 1/2 the radius of the opening in which the lip is located.

I just wish I had access to instruments to test airflow so that I could quantify any improvements, without which, anything I do is for my own benefit only, and can't easily be shared with the community...

As Evanism says you can use a manometer to check for leaks and to get an idea of "is this netter or worse than this"

There is only only accurate measurement that can be made with a simple manometer and that is the static pressure of the system. This is a pressure (vacuum) test done with all blast gates closed and one end of the manometer connected to anywhere in the ducting. This will give you an idea of the Max flow rate using the graph shown in the sticky in this forum.

Dynamic pressure tests. pressure tests done with the air moving in a duct, are unreliable because of Bernoulli effects but if the pressure testing point is kept firmly fixed (in the same place and not moved around, the orientation of the tip must remain the same as well ) then a relative measurement is possible, i.e. "is this netter or worse than this". The becomes useful to test the bends/junctions you describe above, when opening up ports on machines and generally changing things around.

I wanted to reply to each point but doing multiple quotes is a pain on this little iPad.

The manometer is a good idea, I've used one before, for checking the pressure on my bagpipes. I'll have to try that sometime, but for now I've just been focussing my attention on getting it up and running.

Bob, I intend putting a bell on the mouth, I just need to work out how to form the lip in the PVC fitting.

I wasn't sure how to assemble the bit behind the lathe. The main pipe is dangling under a roof rafter, and the down pipe kept falling off. Even with it tied onto the cross piece, it was still too loose to be able to use properly. So instead of using a 45 degree coupling behind the lathe, I put a 135 degree junction, and a spare piece of pipe down to the floor with an end cap on. The spare bit of pipe holds it all up, and makes it quite stable. I can still swivel it to change the angle it suck depending on what I'm working on. I think I'll make a floor sweep on the bottom of the 'foot'. I'd post a pic if I could work out how on the iPad.

I spent a while wandering around trying to decide on the best way to route the ducting, and there doesn't seem to be a really good simple way to do it. I ended up taking it out the side of the garage, and around to the front. This way I can just swivel it around if I decide I need to bold an enclosure out the back. It's not the most efficient route, but it was the best I could come up with. I haven't glued any of the joints, I reckon I might well change the thing so this way I can just pull it apart if I need to try something out.

I tried running it all and sanded a small bowl I started a while back, and it was quite gratifying to see the dust snaking off up the pipe.

There is a definite, non-zero chance that now that it's up and running, I'll not fiddle with it for a while, because it's doing what I want.

Originally Posted by Colin62

Bob, I intend putting a bell on the mouth, I just need to work out how to form the lip in the PVC fitting.

How much swing does your lathe have? If it's big enough make up a 36 mm thick MDF sandwich from 2 sheets of 18 mm MDF and turn the opening in it to fit the ID of your PVC trumpet and also the lip into the MDF.
On the other side turn a rebate equal in Diameter to that of the OD of the PVC. This will enable the MDF to sit on the end of the PVC, attach with hot glue gun or any other method

I wasn't sure how to assemble the bit behind the lathe. The main pipe is dangling under a roof rafter, and the down pipe kept falling off.

To hold PVC pipe in that situation I just use small self tappers that just bite into the internal pipe..

I spent a while wandering around trying to decide on the best way to route the ducting, and there doesn't seem to be a really good simple way to do it. I ended up taking it out the side of the garage, and around to the front. This way I can just swivel it around if I decide I need to bold an enclosure out the back. It's not the most efficient route,

A sensible route often forgotten but can be quite useful - Parisienne Pompidou Centre Style I call that

but it was the best I could come up with. I haven't glued any of the joints, I reckon I might well change the thing so this way I can just pull it apart if I need to try something out.

I tried running it all and sanded a small bowl I started a while back, and it was quite gratifying to see the dust snaking off up the pipe.[/QUOTE]

There is a definite, non-zero chance that now that it's up and running, I'll not fiddle with it for a while, because it's doing what I want.

Those are famous last words