Woo Vacuum Pump!
 

So I just aquired a vacuum pump from a friend... on loan :)

It's a rotary vane type pump that will pull 20"Hg or 25"Hg intermittently.

So, I don't want to fry this pump while vacuum bagging. Therefore, I need a vacuum limit switch. Having very little budget to do this, I'm posting this question to everyone. Any solutions?

Here's the one I came up with... And I do recognize the Rube Goldbergian properties of it. Hook up a syringe to the vacuum lines and on the plunger, hang a weight. Below the weight, place a micro switch. When there's vacuum, the weight hangs above the switch and the pump is off. If the system loses vacuum, the weight falls the switch is closed. This will cost me about $5 (10 cents for syringe and ~$4 for switch), $10 at the most including electrical components.

Diagram
http://www.instructables.com/files/d...P37.MEDIUM.jpg


Thoughts, suggestions, alternatives? Anything blatantly obvious I'm missing?

I applaud your art. :thumbup:

Should I frame it? :p

a spring, and a screw would do the same thing as a weight, and could easly be adjusted.

Don't fry the pump, that would suck. oh wait...

but seriously, you could obviously calibrate it by varying the weight. I'd be concerned about the friction of the syringe plunger. Maybe a lubricant would help as long as it doesn't attack the rubber seal.

I think it belongs on the fridge door.

vacuum pumps uk
 

If you want to find out more about finding a vacuum pumps uk there's some information at the bcas website, it's short for British Compressed Air Association.
Hope it helps.

great drawing, loks like something out of scrapheap challenge

thanks

It's very simple... and it might even work.

If you could design/build an electronic switch, a MAP sensor would also work, but you'd need an Arduino or something similar to read the signal and control the circuit.

Basically, set it up so that the MAP sensor's reading controls a switch. Under 16" of vacuum, turn on, over 18", turn off.

You take an old pill bottle, drill a hole in the top of it, insert the MAP sensor (which needs a 12V/ground as well as a sig output) then drill another hole for a nipple, to which you would attach your signal hose. Run the signal hose in a Tee with the bag hose, so they "see" the same vacuum both inside the bag and inside the pill bottle.

When the pill bottle's vacuum reaches 18", the Arduino kills the circuit (the pump's circuit - leave the MAP turned on) and when the bag falls below 16", the Arduino turns the pump circuit back on.

This way, there's nothing mechanical to align, nothing can slip, break, or otherwise fault, and you can build in redundancy that if the system drops below a certain vacuum level for X time, to turn off the circuit.

Say, for instance, a hose cracks. Pump starts pumping, because vacuum is below 16"... pump can't get anything higher than 10" after 30 seconds, Arduino shuts down pump to prevent damage.

The one I built, which has been in use for years, is based on a rubber diaphragm. I think that the friction in a syringe would cause wide swings between on and off. I used a small,strong tin can from yeast, and bound the rubber drum-head on with windings of rubber strip. The vacuum hose fits on a soldered-in tube. The microswitch is bare, mounted on a hinge, and gets pushed into the drumhead by an adjustment screw. You could probably use a jar, and glue the vacuum hose into the drumhead.