Tear-Down: Edwards RV-8 Dual Stage Vacuum Pump

[PedroDaGr8]

I tore this down a long time ago and published an instructable about it. Decided that I would throw some of the pictures up here as well. For me it was interesting fun, I had torn a few down before but not to this level; usually just to replace a gasket. Other than being messy as bloody hell and quite time consuming, it is quite easy to repair. This device is a dual stage oil pump which means that it has a larger rough pump which gets rid of most of the air and a second finer stage pump which makes an even higher vacuum.



A bit of background on WHY I had to do this:
I was pulling trace solvent out of a metal fatty acid powder and at some point over night it decided to travel up the hose, through my Schlenk line, through the solvent trap and into the pump. Gunking up EVERYTHING. The pump had begun making a loud chuffing and stuttering, which had me worried it had seized or was going to seize at any point. In fact, once I let it cool, it DID seize on me.

So I open it up and it looks like this:


Underneath that cap is the vent hole:


Removing the front cover we see the oil pump:


Here you can see the mess I had to deal with:


Now we see one of the stages of the pump:


The main stage of the pump:


Here yo ucan see the mess I had to deal with:


An example of a rotary vane. You can see how the two vanes slide as the rotor moves:


More example of the sludge that had built up:


All clean:

[SeanB]

Now I know how mine looks inside. I have cleaned some larger ones that are both oil less and run in oil, the oil less ones use graphite vanes while the oil baths use polypropylene blades.

[PedroDaGr8]

Now I know how mine looks inside. I have cleaned some larger ones that are both oil less and run in oil, the oil less ones use graphite vanes while the oil baths use polypropylene blades.

Interesting, I have only used the oil type. I dunno if its because of cost or what. If you don't mind me asking what do you do that necessitates vacuum pumps like these.

I was actually surprised at how well thought out and simple these were to take apart. One single 3/16" allen wrench takes apart the ENTIRE thing. Most things are held together via compression/friction.

[SeanB]

Oil less pumps are used for applications where the vacuum air is returned to the room so you do not have to deal with removing an oil mist. All you need is a 0.3 micron filter block on the outlet side to remove the fine dust it makes as the vanes wear. The oil filled units use the oil for a seal on the sides of the core and the housing ends, and use it for lubricating the bushes and the walls as part of that. That is why they cannotr deliver pressure above ambient, and also need to run partly restricted at all times so that the suction can pull the oil through the feed lines. They have a separator to reduce the oil mist, but will all eventually dump the oil as vapour in the outlet air. The one pump that runs a lot will go through about 2l of oil in a 3 month period, so I simply added a pipe to allow it to vent to the outside so the oil mist was not a problem. The oil less ones can provide a pressurised feed of air as well, though the flow and pressure is very much a result of the inlet conditions, it will do a pretty good flow at low pressure with the inlet open, but less the higher the vacuum you pull. You can recirulate the same air in a nearly sealed system with one.