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LOHAN: Reader vacuum pump plans really suck

Top quality amateur boffinry from El Reg spaceplane fans

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We at El Reg's Special Projects Bureau are, as ever, grateful to all those readers who offered suggestions for the low-cost, garden-shed vacuum pump rig we need for our Rocketry Experimental High Altitude Barosimulator (REHAB) experiment.

Click here for a bigger version of the LOHAN graphicOur bold plan is to stick the proposed power plant for our Low Orbit Helium Assisted Navigator (LOHAN) spaceplane – an AeroTech RC 32/60-100NS rocket motor – into a homemade hypobaric test chamber.

Below is the final concept graphic as to just how that will work, amended from previous versions to take into account your design concerns.

There's more on how the whole thing works here, but for those of you already up to speed on the plan, the only significant change is that the igniter and temperature sensor wires now pass through the top plate rubber seal. This means we don't need to bother with cable feedthroughs screwed into the wall of the inner tube.

Our revised REHAB hypobaric test rig

Note that as as we draw a vacuum, the top plate will be pulled firmly down onto the seal and the wires, and the whole lid should be airtight enough for the short duration of the test.

So, that's all under control, but how are we going to create a vacuum of 15mmHg?

Well, we threw that problem over to you lot, and you can see some of the splendid and ingenious ideas right here.

Your cunning plans ranged from using condensing steam to bloody enormous columns of water, via Magdeburg hemispheres and vehicle air con pumps.

There were plenty of votes for water-powered aspirator pumps, but a quick shufti online revealed that to get a decent vacuum we'd have to shell out a wad of cash – something we're trying to avoid here.

Which is why, of course, we don't buy buy a proper vacuum pump and be done with it.

This leads us to by far the most popular and cost-effective suggestion: the second-hand fridge compressor, which can be bodged to suck and, according to some of you, will deliver the required vacuum.

We shall see, because said compressor is going to be our first line of attack. Rather handily, my local fridge-fixing chaps have promised a couple of units for free, having immediately grasped just what the mad Englishman intended to do with them, and agreeing with Reg readers that the idea has legs.

So, it's a case of suck it and see. If it doesn't work, we'll have a rethink and come up with a fall-back solution, so some of your more esoteric concepts may yet see the light of day. ®

Bootnote

I'd like to offer a very big ta very much to those readers who offered kit they happened to have lying around in the shed for our REHAB experiment. The problem is, you're all in the UK and the US, and I'm in Spain, so it'd end up costing us more to get the stuff here than bodge something locally.

Nonetheless, it's much appreciated.

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