View Full Version : Compressor start in vacum. What is happened?

11-01-2015, 12:29 PM
I have heart many theory that is not allowed to start compressor in vacum. Nobody knows it surely, anyway. I understand that compressor heat up quite shortly when suction gas flow is missing, but has it happened something before that?

monkey spanners
11-01-2015, 02:30 PM
The vacuum makes it easy for electric to jump gaps in insulation and short out the motor. It is the same reason not to megger test a compressor in a vacuum.

11-01-2015, 03:38 PM
In low absolute pressure and thin air/gasses, electrical strength is low and power socket on compressor with glass seal have uninsulated part in welding/press-connection to motor winding. If connected to power and Voltage transient coming on power cords (think stopped elevator in same house) in high vacuum state, transient can ignite plasma discharge without any current limit and destroy inside compressor very quickly.

Think fluorescent lights but without any current limiting.

Or rememberer old incandescent lamps without internal fuses, in 230 Volt world, they sometime pop with glass pieces flying around, but more often bulb starting to melt in some point and make hole and air rush in of 1/10 of second with loud pop depend of burning plasma ignite inside in same time glowing tread fell apart inside lamp

Absolute pressure of Argon is < 0.1 mBar in normal household light bulb, but same time plasma starts is make enough heat to melt glass and pressure enough to bulge out melting glass and make hole in bulb in time of around 0.1 second...

Break down Voltage and ignite plasma discharge in gas describes of a paschen's law http://en.wikipedia.org/wiki/Paschen%27s_law and highest risk for ignite is around 1-10 torr (1.3 -13 mBar absolute)

Fluorescent lights and neon-tube have around 10 torr (13 mBar absolute) as working pressure and if florescent light can burning steady over 40 cm length on only 110 Volt Voltage, think is only ~1 cm between connectors behind glass seal in compressor...

Is why is not recommend running any compressor with embedded electrical motor in stronger vacuum.