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Air Compressor Testing 2001 - Results
Standard air compressor
The first tests were done on the standard air compressor which is here used as a benchmark. The X-axis shows the relative time with 50 pressure readings taken at 0.1 sec intervals. In the graphs, it is important to look at the sustained pressure and not just at the maximum.

Note how the inclusion of the tire pressure gauge degrades the performance of the compressor being tested.


With tire gauge included


Direct to pressure sensor

Mini Compressor

This is the Tiny Lego Compressor by Michael Powell. This pump does not seem to do too well especially with the tire pressure gauge included. 

With tire gauge included
Direct to pressure sensor

Double acting air compressor
This was first tested on the original Ralph Hempels' double-pump compressor. The original design did not give as good performance as the pumps did not achieve full compression due to the geometry.


With tire gauge included


Direct to pressure sensor
Improved Double acting air compressor
Ralph's design has since been improved by mounting two wedge wheels one on top of each driven gear. The small pumps now execute the full stroke with marked improvement in performance.


With tire gauge included


Direct to pressure sensor

The sudden drop in pressure sensor values was due to the pneumatic tubing popping off the T-connector of the compressor - the pressure generated was that great!

Improved double-acting compressor Improved double-acting compressor with slip gear
Improved Double acting air compressor with Slip Gear
To try to prevent the over pressure effect, I tested again after replacing the 24T gear on the motor shaft with the white 24T slip gear with the following results.


With tire gauge included


Direct to pressure sensor
Quad-Acting Compressor
Here are the results on  Doug Carlson's Quad-Acting Compressor which adds another two more pumps to the improved Ralph Hempel's design. Despite the additional pumps, it is not better than the latter design. There is an initial overshoot but the sustained pressure is less than that for the improved double-acting compressor. And it did not cause the tubing to pop off.


With tire gauge included


Direct to pressure sensor
Conclusions
In this round of tests, Ralph Hempels' improved double-acting pump has emerged as the overall winner. It was the only compressor tested that generated sufficient pressure to cause the tubing to pop off.  

Despite having double the number of pumps,  the performance of the 4-pump compressor is inferior to that of the improved double-acting design. I suppose this is due to the Law of Conservation of Energy - the motor can only deliver so much energy which is dissipated to overcome the frictional forces among the 4 pumps. 

The inclusion of the tire pressure gauge distorts the measurements as it is itself drawing a heavy load. It would henceforth be restricted to testing of motor-car tires, which is what it was meant for anyway.  

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