OK, well having given it further thought, I only need a fairly small amount of suction, so I may as well run the cleaner at full power voltage with no air blockage and just cream-off a small amount of the airflow via a fabricated 'tee' piece inserted into the hose. Can't go wrong!
Go hunt up a discarded fridge or freezer compressor - make ideal vacuum pumps.
Vacuum cleaner motors rely totally upon a huge airflow over the motor for cooling. Without this they rapidly overheat.
Why not use the vacuum as is and bleed air in through a branch pipe to reduce the effective suction? Henry vacuum cleaners have a port on the handset to regulate the pull on the carpet. (Most folks tape them closed)
Well more likely to have issues with the variac than anything else, I'd suspect, however do remember that the airflow inside the cleanner cools the motor. If it overheated, then there is usually a thermal cut out in any case. Brian
That will almost certainly trip the thermal overload, probably in about 10 minutes or less. I have a Basch and what that seems to do if there is a blockage is throttle the motor right back and stay that way till it is cool enough. Brian
Yes he would be better of fitting a tube with two inlets, so the air coming in through one tube will be at the pressure desired then he can do away with the variac. Brian
Before we get bogged down in who invented the vacuum, let me say just this. When we used to use thermionic valves. Tubes to our American readers, getting the pure vacuum was eventually done by burning the last part of the oxygen and effectively locking it up in the resulting solid which coated the inside of the glass, a silvery black colour in a vacuum. Even in the ISS when they depressurise the air lock saving the air as much as possible they cannot get it to a vacuum, since its got nothing to suck against if the bits that are left are not near the pump intake. Suction in a vacuum is not much use!
Brian
That's Welsh, shirley.
You could do something similar to what a Henry vacumm does with a hole on its handle whose size is changed by a sliding cover.
The (3A) fuse in the variac did blow first time I tried the idea. I hadn't done any sums and hadn't twigged that 1800W would overload it! However, replacing it with a slow-blow type of the same rating enabled me to run it at 80V for an hour no problem. I just had to wind 'er up to 220V at the beginning to overcome the motor's inertia, then quickly backed off to 80V once it was running.
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