DIY vacuum-pump? (for vacuum impregnating)

Search Ebay for something like an Edwards Vacuum pump. Though generally heavy little buggers.
Wayne...

Make sure you include "edwards" in the search or even better "edwards vacuum pump" some very strange things on eBay...
:-)
Steve

Have you any articles on the coil construction? I'm building a four stroke but abandonded spark ignition because I couldn't find any home brew in this space.
Steve

One rule-of-thumb way to think about it is to assume that the air remaining will compress to atmospheric pressure and leave holes (voids) in the filling material. Thus -0.85 bar will leave 15% voids.
You need about 5 mbar (0.5% voids) or so to do vacuum impregnation professionally, though reasonable results can be had at pressures up to about 50 mbar if a layered approach is used (impregnate only one or two layers at a time).
The "paint" normally bubbles in the vacuum, as dissolved gas is given off. This also allows any remaining air in voids to dissolve in the "paint" once the external pressure is raised, so leaving no voids at all (in theory ...).
Two fridge pumps used in series as a vacuum pump might give somewhere around 10 mbar, or even less, depending.
Probably available for free, but use an oil recuperator (the pump outlet goes straight up into the bottom of a container with holes in the top and perhaps filled with some - ???what do you call those things people sometimes use to clean dishes, they are made of plastic or metal ribbons about 1/10th inch wide and look like doughnuts without holes??? - when the motor is switched off the oil which has collected in the container drains back down into the pump).
Peter Fairbrother

Edwards are the classic vacuum pump manufacturer and turn up fairly frequently on Ebay. However they're over kill for a one off impregnation cycle.
For occasional use, provided you've got a zero leak setup, an old sealed unit refrigerator compressor run as a vacuum pump is good enough. It can also be further improved by using your injector pump as a backing pump on the refrigerator outlet.
Jim

When we did VPI on coils at GEC Machines, the P bit was significant as well... Vacuum Pressure Impregnation.
Vacuum to get rid of most of the air and 4-5bars to force the resin into the coils. Just atmospheric pressure can leave significant voids that will lead to partial discharge erosion of the insulation on HT windings. This applies to Nick's first impregnation phase.
Mark Rand RTFM

I have some sort of vacuum pump driven by a single phase motor that is not used. I haven't studied the thread properly as its too early. Will photograph it today. Bob

No articles. It's a bit complicated. The coil I have built (version 2) is quite small. OD 23mm, length 40mm. Sizes for just the coil. Some pictures:
The test setup with my first coil (OD 30mm):
The V2 coil compared to the V1 together with the housing:
And the finished coil:
Neat, isn't it? :-))
Problem is, without electronics, it will not work. The coil is charged with 20 A for 0,5 ms. It can't be loaded for a longer time, because of its low resistance of the primary winding. This coil has a energy of 50mJ, in cars you find 120mJ. To make the coil even smaller, I'll have to find out what the minimum energy in the spark is. Maximum voltage is about 8kV.
Electronics is more ore less a IGBT and a suppressor diode to limit the primary induction voltage. I had 400V induction voltage but now will switch to 500V. A IGBT is fast enough, no problem. Initially I thought it won't work. Can't scope the high side of the coil. No 10kV HV probe here and to expensive. Just bought a 2.5kV probe for the primary side.
The processor is a Propeller from Parallax. Software now is ***very*** primitive. This is next to be done, beside making better coils. Anyhow, it's running on a single 87ccm 4 stroke.
Here is the data for the coil: Core is a Micrometals P2448-240. primary winding is 100 windings of 0.95mm, secondary is 1500 of 0.2mm. The later being double isolated (IIRC 3.5kV). and isolation layer (Polyester sticky tape, 0.06mm, 4.5kV) between each layer of windings. I tried TEX-E wire for the 0.2mm wire but it makes you poor, is thicker and doesn't make things better. The isolation now should be on the save side, so the coil can be used "open" (no spark plug connected). If someone is verifying my data and finds some errors. Yes Amp-windings is high! Design isn't finished, because electronics and coil have to match and its a bit of try and error. Tweak this parameter, tune there ...
I'm expecting to get about 50000 sparks per minute. But I'll see...
Nick

On the European side of the channel you're more likely to come across Haereus vac pumps although I _believe_ they may all be the same company now.
Richard

That was my model too.
Good numbers thanks. Can't impregnate layer by layer or I'll get mad. I found an article describing vacuum impregnation. So I'll have to change my setup and feed the "paint" (what's the right word? Mine is PU) from the bottom through a valve.
I'll try a similar setup. Have a fridge pump (airbrush compressor) and will connect the injector to its back-end and see what I get.
Also thanks to the other repliers!
Nick

OK. That might be the "bumping" I found in an description. But they didn't give any numbers.
And I just wanted to build a new engine ...
Nick

No disfunction here. :-))
Nick

Hope I have read this correctly - Hemingways new IC engine booklet has some ideas and parts.

Old fashioned cam operated fuel pumps were very good for providing pressure and vacuum - if you can still find any!

Do you mean this stuff?
Childish.
Nick

Guess what !!! Mine is an Edwards high vacuum pump !!! Bob

Nick, the English term would be varnish rather than paint. Martin

Or was "bumping" the description of shaking/knocking the part to loosen/remove any bubbles that were sticking to it?
Mark Rand RTFM

That was bumping the vacuum. But on my first coil (layers not well wound) that moved the wires around under the final insulating layer. Some lessons to learn, but getting better ...
Nick