RareEarth - 25-10-2015 at 19:11
There's a lot of different positive displacement pumps on the market. Even some new "silent" external gear pumps, that make next to no noise. I notice
a lot of vacuum pumps are rotary vane, but this is not a requirement. A lot of the new pumps on the market are gear pumps.
I've been eyeing these for a while, but I can only imagine how expensive they are.
https://www.youtube.com/watch?v=_FANj3xDA38
If building one from a motor + gear pump head, you could even use gear multipliers to get super-low vacuums, albiet at a slower vacuum pull rate.
I can imagine a number of different set ups. What all would be needed to add to such a positive displacement pump to make it suitable for pulling
vacuums for chemistry purposes? Bleed-tube regulators of some kind to avoid pulling too much of a vacuum?
macckone - 25-10-2015 at 19:29
The pumps in that video are multistage.
The first one has vacuum control.
The second is a low volume rotary vane pump.
The third is a high volume pump but I could not find the number of stages.
Rotary vane pumps are used because of low noise.
Piston and diaphragm pumps are noisier.
Gear pumps are similar to rotary vane pumps but for liquids.
Centrifugal pump are very high volume but low pressure differential.
Turbine pumps are centrifugal pumps in a multistage setup.
Diffusion pumps go from low pressure water venturi to high vacuum mercury diffusers.
Water venturi is fine until you need truly low pressure.
Most people go to either a diaphragm pump or rotary vane pump.
From there to ultra low pressure you need a diffusion pump.
And below that you have to go to gas scavengers.