LuckyWinner
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Run Vacuum Pump with Relay Timer (On 2 Sec Off 60 Sec)?
I have a PTFE lab vacuum pump that makes a lot of noise.
I put it inside a wooden box with noise reducing foam.
noise is reduced a lot ..
but i also want to use a relay timer.
I noticed my vacuum gauge starts slightly moving after 60sec of vacuum.
would a relay timer , 5 sec on, 60 sec off , repeating,
work to successfully distill liquids with BP of 250C in 250ml flasks x 2
I tested it and my cheap gauge seems to stay steady at ~(-)1 BAR.
does it really need to run 24/7 to achieve a full, steady vacuum that is needed?
[Edited on 8-8-2020 by LuckyWinner]
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Dr.Bob
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For a real distillation the pressure needs to be constant, and trying to turn the motor on and off will make it a mess. Also, most motors strain on
powering on, and create a lot of heat and power surge, so that might fry the motor quickly. Putting it in a box will also heat it further. I think
you are not going to have much luck with cycling the pump. I have run PTFE pumps for days at a time without a problem, so unless it is real crap, it
should be fine. Get some ear plugs, they are cheaper than a new pump. :-)
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BromicAcid
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Quite hot to you might actually be a completely normal operational state for the pump. When you box it in though to kill the noise the insulation
might actually make it run abnormally warm. I would recommend that you start with reading the manual on the pump to see if its rated for continuous
duty. If so it might be best just to leave it running. The manual may also have temp specifications for the pump (less likely). I bought a cheap
relay timer from the home improvement store sometime back for 120V appliances. I needed it because the float on my sump pump had failed, was able to
turn on the pump for 30 seconds every 90 seconds which is similar to what you are going for so such things do exist though this wasn't a brand named
piece of equipment.
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monolithic
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How hot is "hot"? My diaphragm pump reaches 45-48 C around the heads and the motor housing. It's run fine like this for hours on end. Most vacuum
pumps are going to run around this temperature. I also have a belt driven rotary vane pump that gets around this temperature, also runs just fine for
hours on end.
If you're regularly distilling high boiling point compounds than maybe consider a belt driven rotary vane pump. Once it reaches vacuum the sound is
pretty quiet, much quieter than my diaphragm pump. Sometimes you can get lucky and find old Welch, Precision Scientific, Hyvac, etc. pumps for cheap.
Direct drive pumps also work but they're a bit louder since the pump head spins about 3x faster: 500-750 rpm belt driven pump vs 1700 rpm direct drive
pump.
[Edited on 8-8-2020 by monolithic]
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Heptylene
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I'm assuming if your pump is PTFE then it's good quality. PTFE is such an expensive material that I can't imagine it ever gets used in cheap pumps.
Anyway good quality vacuum pumps can run uninterrupted for days. I've run mine (KNF brand) for several days without any issues. It gets warm but
that's it.
To achieve a steady vacuum, run the pump continuously and have a controlled leak the control the vacuum level. I use a needle valve for this and the
vacuum stays constant as far as I can tell from my Bourdon gauge. It was reliable enough for vacuum distillation of nitric acid, and the distillation
head temperature was constant.
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Fyndium
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My pump heats up pretty quickly, but after that the temp just sits there. It's just a thing called operating temperature.
For noise, you might wanna make a plywood box with 30mm sound insulating panels and make noise insulated ducts of 1-2m length on both ends and a small
fan on the other end to circulate air through the box. This can make the pump very quiet.
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