[brokenrinker]

Could this toy design be modified so that it might actually move some air?
I'd like to keep a helical vane. This pump is intended primarily for show. The end pieces are not shown for clarity.

[keebler303]

If it is designed like the real thing, it will work like the real thing. With a tiny model, the tolerances become quite important as the leakage will represent a substantial part of the total flow. This is less important on a bigger model.

So what is your question? Of course it's possible to make it.

[brokenrinker]

The point is - I don't know what the "real thing" looks like. I just made this thing based on images on the net w/o any real knowledge of the principle. My primary purpose was to make something interesting but not too complex on a 4 axis machine. Once I got into it I thought it would be cool if the device could actually pump a little.
It seems like the interior of the housing has to be designed in such a way as to seal the vanes at the proper time. I'm having a hard time visualizing how that should work. The whole principal is changing displacement as the vanes rotate - isn't it?

[Al_The_Man]

There have been several ways over the years to seal the vanes, one method I came across many many decades ago was the pump lobes had grooves machined in to take a graphite strip or slat, this allowed centrifugal force to keep the strip in contact with the cylinder walls.
Many large industrial compressors are now vane type, not sure what the current method is, but I know they run at extremely high RPM.
Al.

[dmalicky]

That's usually called a Roots blower or Roots supercharger. It's used by ~all dragsters and a few cars. As pumps go, its niche is to generate fairly high pressure and moderate flow rates. Air is pumped around the outside, while the space between the rotors is just for sealing.

The shape of the vanes is important to prevent leakage between them -- the traditional design is cycloidal:
Roots-type supercharger - Wikipedia, the free encyclopedia
The outer housing is simpler, to follow the circular arcs of the lobes.

A substantial helix angle smooths the flow, as zero or small helix makes loud pressure pulses. But that won't matter as much for a model that doesn't generate high pressure. It could be fun to have it inflate a balloon.

The lobes rotate in opposite directions by gears. Traditionally, the lobes can't drive each other because each lobe fits inside the other -- see the wiki drawing (technically, the pressure angle is 90 deg). But with the right geometry, I think the lobes might be able to drive each other for a toy model--use a high helix angle and length, and probably go to 4 lobe rotors, so there is a lot of "overlap" between the ends. For example, whenever one end disengages, the other end has good engagement. I'm not sure how much overlap is needed for smooth motion, though, and a stop-start condition is still likely. Gears are cool for a model, so I'd probably use them anyway.

Here are some tiny Roots blowers:
Basic Design, Superchargers

[skippy]

Don't know what size you're after but check out Dzuari's excellent thread here:
http://www.cnczone.com/forums/i_c_en...ercharger.html
You'll notice that prior to making the real thing he made some beautiful 1/2 and 1/4 scale blowers (which you can order at what I reckon is a cheap price) using a high quality (professional) 3D printer. I can't post the pictures because for some reason when I went to the thread now I'm only seeing the icon for the photos instead of the photos themselves. Anyone know why? Where's the problem? my computer? cnczone website?

[brokenrinker]

Good suggestions - Thanks!
dmalicky - the link to the tiny roots blowers is especially helpful. Those guys are making some really impressive stuff. I like the idea of inflating a balloon with it.