Fusor Forums

Was finally able to do some foreline testing with my thermocouple gauge and 2 stage pump today, had some leaks at first but eventually worked it out and was able to get the vacuum down to what appears to be 15-30 microns (Rough Estimate). Hoping to get the rest of my chamber parts next week and I'll be able to test the Turbo Pump.

Thermocouple gauge

Your gauge head does not read microns! Obviously, units of torr (that is, millimeters of Hg!) That gauge can tell you that "The pump is running" but is useless for working with a fusor (However, very useful for sputtering systems or as a fore-line gauge. If either of those applications are its purpose then that gauge head is excellent.)

So how are you determining that you reached 30 microns? I seriously doubt the scale is accurate much below 100 microns and even that reading is likely +/- 20 microns or worse unless the unit is new or was recently calibrated - in which case the mfg instructions will provided the reading accuracy.)

My two stage surplus pumps both get me down to a few microns at worse (and after drying the oil using the air vent valve for an hour or so, under a micron) and those readings should be typical for that type of pump (the former, not necessarily the later.) Your pump might very well be reaching under 2-3 microns and you'd still read 30 microns or so using that gauge head/read-out unit. You need a proper micron scale gauge if you ever want to get useful readings with a two stage vacuum pump.

Dennis has a point, but your gauge does probably indicate you are, indeed, in the range of good demo fusor work, assuming it is in some sort of decent calibration. For proper fusion work you might want to acquire a normal and typical technical vacuum type foreline gauge that reads in microns. The investment is worth it.

Richard Hull

Thanks for the insight, I understand the inaccuracy of my current gauge head and I'll keep an eye out for a better gauge readout.