Home      Projects     Experiments     Circuits     Theory     BLOG     PIC Tutorials     Time for Science

 DIY Small Size Air Compressor on the Cheap AuthorGiorgos LazaridisAugust 17, 2012

PAGE 4 of 6 - Testing the performance of the air tank and the compressor

So, let's make a first test of the compressor. I really had absolutely no idea if the small air compressor would be enough to fill the container with air at 9 bars within a small time, because (as per specs) the pump can only work continuously 10 minutes MAX...

 This is the test setup. The pump is powered from a PC PSU, an ammeter will measure the current needed for the pump. A timer will keep track of the time The current started from 3.5 amperes and climbed fast at 5.8 amperes when the pressure reached 6 bars The time to reach 6 bars was only 2.5 minutes! That was better than i expected, but then a problem occurred This connector failed to properly seal the tube, so at 6 bars the hose leaked...
 I replaced the sealing collar with a pneumatic quick self sealing connector The second test began with a higher current, about 4.5 amperes This time, the pressure reached 7 bars at 2.5 minutes It took 2 minutes and 40 seconds to reach 8 bars! Excellent performance!

 The current at 8 bars climbed up to 6.6 amperes...

Better than expected!
Indeed, much better than expected. I takes less than 3 minutes to get a pressure of 8 bars, so the small compressor operates way bellow its limits. The 6.6 amperes current is a very reasonable current to handle with a simple PSU, probably switching.

Then, i made another final test to see how good the construction is sealed. Without removing the compressor, i measured how much pressure escapes form the tank:

It took some 25 minutes for the pressure to drop from 8 to 6 bars. This is a rather poor performance. I am thinking of using a one-way valve between the tank and the small compressor, because i think that 99% of the loses comes from the poorly sealed compressor...

Generally, i am very pleased with the results.

What about the air capacity? (October 17 2012)
In the first page of this project i did some calculations to see if the volume of the air in the tank is enough - but now things changed. The pressure range is now from 5 to 7 bars. To avoid doing the same calculations again, i made a dirty spreadsheet to do the calculations for me. Here it is:

Tweaking the calculator? (October 21 2012)
The idea is that i will use a 3-way (or 5-way converted to 3-way) pneumatic valve to actuate the piston. The purpose for the 3-way is that i want the compressed air in the cylinder to be exhausted upon release, so that there is no remaining pressure. But this means that in my calculations, i have to include also the hose air volume, since the air in the hose will also be exhausted. So i made another spreadsheet with the hose volume included: