This past winter while sucking on a piece of rubber tubing, and trying to keep the other end on the baro sensor to test a altimeter, i knew there had to be a better way. And then it hit me, a small portable vacuum chamber, would be just the ticket. Only problem was i had never seen one for sale, or the plans for one. No problem, i would just design and build one. Of course it never turns out to be as easy as one thinks, but overall it was not too bad.
The first thing i did was to look around the shop and start gathering things up that i would need. A small piece of plywood for the base, a 12 volt tire inflator, on which i would reverse the fittings and turn into a vacuum pump, a small lead acid battery for power, a piece of pvc pipe for the chamber, a piece of lexan for the top, a couple of valves, some brass tubing and hose, a couple of terminal strips and wire, and a small case to put it all in.
This was going to be easy, i had everything that i needed, and did not spend a dime. Sure. First thing i did was to tackle the pump. Long story short, the tire inflator did not work. Not a problem, i had another 12 volt tire inflator that i would use. After another hour or two, i now had two tire inflators that would never inflate another tire, but still no vacuum pump. Well i was sure that i could find what i needed on ebay. Turns out that i did, a used, small 12 volt vacuum pump for only $4.95, but wait, shipping was $15.00. After looking on ebay every day for a week, and finding nothing else, i went and ordered the pump. If it did what i wanted, i was ok spending $20 on it. Turns out it works great. Next i built the vacuum chamber. I cut a 7 inch long, piece of 2 inch pvc tubing length wise a little above center, added a couple of end caps and a top of lexan, drilled a hole in each end cap for fittings, addded a rubber seal on top, and drilled six holes for the connection wires. It looked good and seemed to work fine.
At this point i hooked the pump up, put a altimeter into the chamber and turned it on. It did not work. Turns out that the pump does not pull a vacuum smoothly and evenly, it sort of work in jerks and drove the altimeter insane. So, a storage chamber for the vacuum would be needed. I had some 4 inch pvc and a couple of end caps, so i cut a piece that would fit in my case, drilled and tapped one end cap for fittings and cemented it together. Another quick test showed that this was the answer.
At this point i was ready to assemble it. I cut the plywood to fit my case and stained it. Painted the storage chamber blue, with some left over spray paint and mounted it, Built a hold down for the battery, and installed a on-off switch on the pump and installed them. Added some hold downs for the vacuum chamber, installed the terminal blocks, and hooked them to the wires coming from the chamber. Connected the pump, storage tank and vacuum chamber together with brass tubing and hose, installing the valves where needed. Added some labels to the terminal strips and i was done.
It works great. In the end, the only out of pocket cost was $20 for the pump. If one were to purchase all the parts new, i think it could be built for $80-$100. I added a few pictures and a short video of it in use. All comments and ideas on how to make it better are welcome. If someone decides to build one, please feel free to pm me for any information or help you might need.