Magpie
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vacuum pump noise level
The noise that a vacuum pump makes is an important characteristic to some members. This can depend greatly, I think, on whether the pump is moving a
lot of air (or gas) as in a Buchner filtration, or whether it is "deadheaded" as in a vacuum distillation. In this last mode it is moving very little
air (or gas) and is mostly just making up for the minor leakage at the joints.
I have a single-stage, oiled, Harbor Freight (HF) vacuum pump which I use for vacuum distillations (I use an aspirator for the Buchner). Because a
member asked me if it was noisy I made a YouTube movie to demonstrate the noise level when deadheaded (suction valve closed). In this mode it is
moving no or very little air. The oil circulation, fan, and fins provide all the cooling that is necessary for this pump to run for hours at a "warm"
condition with no danger of overheating. I do not find this noise level offensive.
I invite others to post such videos, at deadhead, of other style vacuum pumps for comparison.
https://www.youtube.com/edit?o=U&video_id=1SNNARV5z3M
The single most important condition for a successful synthesis is good mixing - Nicodem
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morganbw
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I get no video with your link?
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Magpie
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Sorry. Try it now.
Edit: Now the #%* sound is off. I'll fix that too. 
Edit 2:
OK - someone please tell me how to activate the sound.
[Edited on 5-4-2015 by Magpie]
[Edited on 5-4-2015 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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smaerd
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I'll see if I can get my diaphragm pump up this week unless someone beats me too it. Doesn't pull a high-vac but it's pretty quiet (why I selected it)
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Zombie
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I don't have a Vac. pump yet but sound level is the single most important factor (for me).
As long as the pump does what I need it to do, it has to be silent. I plan to mount mine either under the floor joists (Crawl space under the house)
or in a built on container/housing on the outside wall near the flow hood outlet.
I'm a finicky sort, and don't like noises. Vibrations are worse for me.
I did the same thing when I raised fish... all the pumps were mounted in the basement.
They tried to have me "put to sleep" so I came back to return the favor.
Zom.
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Magpie
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My pump is sitting on my wood bench made of 2x8 planks. This is probably amplifying the noise somewhat. But that is where it sits when I'm using it.
I don't think I've ever had it running for over an hour. So it doesn't bother me. Now if my neighbors had yapping dogs...well... some kind of
action would have to be taken. 
The single most important condition for a successful synthesis is good mixing - Nicodem
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Zombie
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Quote: Originally posted by Magpie  | | My pump is sitting on my wood bench made of 2x8 planks. This is probably amplifying the noise somewhat. But that is where it sits when I'm using it.
I don't think I've ever had it running for over an hour. So it doesn't bother me. Now if my neighbors had yapping dogs...well... some kind of
action would have to be taken. |
No offense... I have seven mean ass dogs... I feed my neighbors to my dogs.
Not really but none of them have attempted to complain. (we also have Gators, and Bears that are within 100 yards of home so the dogs are welcome)
They tried to have me "put to sleep" so I came back to return the favor.
Zom.
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Fractionator
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Here is a working link to your video Magpie:
https://www.youtube.com/watch?v=1SNNARV5z3M
I went out and purchased the same vacuum (except mine is labelled Pittsburgh Automotive?) and I'd say your video sounds similar. The only difference
is that when mine is pulled deadhead, when it reaches max vac it has the "zapping" sound. Yours doesn't seem to be "zapping"... Are you sure there was
no bleed in the system? And I don't mean zapping like electricity, it's just the best way I can think of describing the sound.
Mine sounds a lot more like this: https://www.youtube.com/watch?v=C--7tiiODIY
Perhaps there is a difference between the General and the Pittsburgh models.
I made a ghetto-manometer by filling 4mm PVC hose with vacuum oil and sealing one end with a clamp. It pulls it below level, which is a
head-scratcher, but gives me a good feeling. I hope to throw together an Anschütz/Bennert manometer w/murcury when I get a chance and repeat the
experiment.
My last pump was quieter in the sense that it didn't do the "zapping", but the last one didn't pull as hard, so I'm thinking perhaps the sound only
happens at extreme low pressures.
Your posts urged me towards this vacuum, and I'm glad of it; I certainly do not need a double stage unless the physics bug bites me. This brings me to
wondering.... now I have 2 single stage vacuums: if rigged in series, what sort of bad stuff would happen? 
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Magpie
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If there was a bleed into my system it would be making more noise, not less.
That pump sounds like it's cavitating a little. This could be caused by gases being sucked out of the air conditioning system. I wouldn't expect to
hear that from a deadheaded pump.
I don't know what the "zapping" noise could be - maybe just a characteristic of the Pittsburgh brand.
If you put the two pumps in series you should have a 2-stage system and should get a deeper vacuum. But if you are already down to 1mmHg with one
pump it may be hard to tell the difference without a very sensitive vacuum guage. Like you say, for most all vacuum distillations, it doesn't
matter. I've never tried that - maybe someone else has?
[Edited on 9-4-2015 by Magpie]
[Edited on 9-4-2015 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Fractionator
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Ok, I just fired it up deadheaded right at the valve, and now it sounds very much like your video (perhaps a bit louder, but no "zapping"), just
normal electronic motor hum with an occasional blurp. I'm pretty sure that the Pittsburgh brand is the exact same machine as the General brand, I
think it's just a different badge, but I could be wrong. They look exactly alike in every other way.
I am glad you brought up cavitation, because that is what it sounds like, and I've come up with a hypothesis why it may be happening in my case. When
I put together my ghetto manometer, I made it about 2 meters long (way longer than necessary). I pulled the vacuum until the fluid was level on each
side (15mm below closed end), then I lifted the closed end as high as I could to see what would happen; that's when I started hearing the sound.
Perhaps I caused the system to drop below the vapor pressure of the vacuum oil.
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Zombie
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When a piston vacuum pump starts "zapping" it is usually caused from play in the connecting rod, flywheel/crankshaft.
What happens is the vacuum stroke is strong enough to pull the bearing or fitting parts to one a side skew. As the vacuum stroke ends the force is
exactly opposite, and you will get a mechanical clicking from the parts.
Cheaper pumps are mass produced, and the tolerances will vary.
Adding 2 different pumps either in series or parallel is NOT a good idea. One will always be stronger, and have a negative effect on the weaker pump.
You can pull down large volumes quicker but as soon as vacuum appears to slow down, remove one pump from the system.
I would recommend parallel for this type operation.
I use vacuum pumps, and silicone bags for carbon fiber fabrication... Been there done that.
They tried to have me "put to sleep" so I came back to return the favor.
Zom.
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Magpie
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I agree that for pulling down large volumes 2 pumps in parallel would be quicker. But for chemical bench work, like Buchner filtration, it seems like
the 2.5 CFM from a single pump would be plenty.
To get the deepest vacuum from a system that is already evacuated, as in vacuum distillation, I would think two pumps in series would be better. This
would be akin to using a booster pump in a water pumping system.
But this is theory. I'm not speaking from experience here.
Would these small vacuum pumps use pistons? I would think that they would be vane pumps or gear pumps. But the sloppy tolerance theory might still
apply.
[Edited on 9-4-2015 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Zombie
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Looking up the parts list I see they are rotary vane pumps.
http://manuals.harborfreight.com/manuals/98000-98999/98076.p...
As you said Magpie. I believe the reason(s) for the noise remains as I stated. Tolerances...
They tried to have me "put to sleep" so I came back to return the favor.
Zom.
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