organicchemist25 - 14-10-2017 at 17:06
I have a vacuum pump (Chemglass) that is overheating and cuts off. Then when it's cools back down it starts back up, then heats up and shuts back
down. It's a high dollar pump and has all ptfe internal components. Hate to just say it's trash. Has anyone else had similar issues with their pump
during reduced pressure distillation? I had a stir at going. Had a good pull too. About 10 torr. The pump was HOT when it shut off. Any ideas or help
would be appreciated!
Should I send it off to get rebuilt or worked over?
NEMO-Chemistry - 14-10-2017 at 18:00
Has it always behaved this wauy, or is this new behavior? I ask because if this is something new, then maybe the pump needs a service, some part of it
probably the motor bearings or maybe the brushes might need looking at.
Most vac pumps tend to get hot, also most have a max run time stamped on them somewhere or in the specs. I have a twin vane rotary type vac pump, it
pulls a very strong vac. i was a bit perturbed to discover it says on the plate to run for 10mins!! then leave for 30 mins.
I do use it for alot longer than ten mins, but i keep an eye on the temp. My complete guess would be maybe the motor brushes are getting worn, but its
just a guess. How long you running it for?
organicchemist25 - 14-10-2017 at 18:26
I have had it about a year. But, I don't really use it much. It was used more for vacuum filtrations. I never had a problem. I'd say I let it run
about an hour, but I think it had cut off once before. I had stepped out of the lab while I was waiting on it to reach max vacuum. I came back in and
was messing around (fume hood was on) and I didn't notice it was off. It's quiet. It just started back up. Then I noticed it. So, I let it keep
running. It got hot again and cut off. Sucks. Thing pulls good and is quiet.
I'll look tomorrow to see if I see a max run time. What am I supposed to do for a 3-5 hour reduced pressure distillation? I guess I could get an
aspirator or make a recirc one to save water, but I'd just want a vacuum.
Thank you for your help.
[Edited on 15-10-2017 by organicchemist25]
Reboot - 21-10-2017 at 16:49
It sounds like a classic thermal overload protection tripping problem. Sometimes it's just the thermostat (pretty much all larger motors have one),
but since you say it was quite hot I assume it's really overheating.
One way this can happen is if the pump is turned off (or loses power), then restarts against hard vacuum. The electric motor often can't quite get
rolling again against the resistance of the vacuum, so it stalls and overheats.
It could be as simple as an airflow problem (for instance, lint buildup in vents/motor.) Start there; look it over, maybe blow it out with compressed
air.
One silly problem you see now and then is somebody trying to run a 220v motor at 110, but I assume that's not the case here. :-)
Sometimes motors overheat because a mechanical failure is making them work much harder (like a bearing going out in the pump mechanism), but that
would normally produce some odd noises (rattling, squealing, etc.)
Perhaps you're just exceeding the duty cycle of the motor, but that seems unlikely; pumps like this are quite expensive and usually very heavily
built.
If you can't figure it out, I would just take it to an electric motor repair shop (one of those odd specialties that you don't think of, but any
medium sized or better city will have a shop or two around.) They should be able to figure it out and fix it for a reasonable price. Companies
rarely build their own motors; it's a very safe bet the motor is something off-the-shelf, probably even fairly generic. If needed, it shouldn't cost
a fortune to replace, Maybe $200-$500 depending on what it is.
Good luck!
organicchemist25 - 29-10-2017 at 12:46
It's at an electric motor rebuild company now. Dropped it off Friday. They said they will look it over and test the capacitor and see if there are any
amperage issues. Hopefully, they find something significant and and is able to be fixed. Thank you for the reply.
One thing I didn't mention is it has airflow out of the blow side, but when I hook up vacuum side the air stops blowing out. Idk. Never noticed if it
did that before, but I have 2 other vacuums (not as good, but decent) and they still exhaust air out of the blow side while vac is applied. So, that
may be something I look into if they do not find anything.
Reboot - 29-10-2017 at 13:19
For a pump to move air when there's little resistance but to stop once you connect something to it suggests that there's a problem with either the
check valves or the diaphragm(s). (I assume the motor keeps running normally when you block the inlet; if it's stalling, that would explain the
overheating as well.)
I would pop open the pump heads and take a look. They aren't too complicated; the bolts in the top hold together a stack of components, with the
valves just under that top metal plate (usually just a flap of teflon over a hole) and the diaphragms on the bottom of the stack (between the metal of
the case and the thick cylinder of the heads.) No need to be afraid of pulling them apart, although it can save trouble to take some photos as you
go to make sure it goes back together the right way. Once open, I'd look for damage to the valves (the surfaces will typically be smooth), material
fouling the mating surface that the valves close against, and look for cracks in the diaphragms.
Replacing the diaphragms is an almost inevitable part of long-term service for this type of pump; eventually they wear out, like tires on a car.
NEMO-Chemistry - 29-10-2017 at 20:32
I agree, it sounds alot like a valve issue which is good news. There is a high capacity air pump used for running fish houses, they are like your vac
pump but in reverse. The one I had ran for around 2 years no problem then stopped working, mine turned out to be a black tar like stuff that had stuck
one the valves shut.
The bad news on mine was the thermal cut out didnt work so I lost the pump, mine ran 24 hours a day every day though, its amazing how much gunk is in
normal air!! The other issue might be the capacitor (big possibility), but if your not getting airflow then it has to be more to do with a valve etc.
Considering you use it for filtering i think it likely you worn a diaphragm or valve out, shouldnt be expensive and next time it cuts out you will
know what to do straight away 
.
Good luck!
p.s
Also might be a good idea to make sure it always has a good airflow to keep it cool in future. Says he who has a oil vac pump with 3 year old oil in
it like syrup now . I will change it.....one day