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Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
Does anyone have the HF 3 CFM, 2-stage vacuum pump? If so did you ever measure it to see how low it'll go?
It's advertised as being able to go to 25u, but mine seems to bottom out at 50u, and that's with a TC gauge right at the pump inlet with no other load attached. I'm going to go ahead and use it to encapsulate the coils I made, but the unexpectedly poor performance of the pump has me a little irritated.
Apparently it's hard to find an inexpensive yet half-decent vacuum pump these days.
Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
What's the vapour pressure of the encapsulating agent? If it's got styrene in it you won't get anywhere close to 25µ before it boils. The vapour pressure of styrene near room temperature is about 5 mm Hg. That will mess up the pump as well as not really helping the coils. Also, how good is the gauge? What did you check it against? Did you run the pump for a while to warm the oil and purge out water etc before checking the vacuum?
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
I'm not sure what the vapor pressure of the epoxy is, but it's intended for vacuum encapsulation, so I would hope that it doesn't have volatile stuff in it.
In any case, the TC gauge is a Varian (I forget the model) and it uses a Varian #531 tube.
I used to have a Dosivac DVR-95 pump (which was rated at 15u), and when I tested that pump, it buried the meter (when it wasn't leaking, that is).
I got frustrated with the Dosivac because the inlet fitting had a design flaw and it leaked around the built-in valve. I tried making a replacement inlet fitting, and it worked ok when it worked, but it would still leak sometimes, and there was nothing I could do to improve it because the inlet port did not have a tapered (pipe) thread, and there was just not enough room available around the intake port to install a robust o-ring-sealed fitting. So I ended up selling it on ebay, and I replaced it with the HF model.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
I have actually been thinking about making a thread about the same pump, the only pump i have is an air conditioner's compressor, which can get down to around 1 Torr (or so i heard). I don't even have any money right now, but if they can't even get to the rated vacuum, i won't be buying one anyhow.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
I ran it again. This time I let it run for about 10 minutes, and it got down to about 35u after 7 minutes, and didn't move after that.
That is probably good enough for what most people would need, but the Dosivac pump I used to have was much better.
Anyway, I then hooked it up to my vacuum chamber, and after about 10 minutes, it hit 200u, which is probably more than sufficient to de-air the epoxy. (I think I will try to do the epoxy encapsulation tomorrow).
In the future, though, I plan on doing some electron beam experiments, and for that application I would like a better pump. My problem is that I don't want to spend more than a few hundred dollars on one.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
50 to 100 um is fine for common electrical encapsulating. i think it will go to 25um if you really dry the oil for many hours, that 35uM after 7 mins is pretty good even if only a small volume was pulled to that low of a vacuum. Thats pretty good. When i get the time/money I was going to start a project thread on how to do this.
I think youll be fine, so start to practice your skills.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
If I never had the Dosivac pump, I probably wouldn't be complaining about the HF pump right now. The Dosivac took all of about 2 minutes to bury my TC gauge. Now that's performance.
Anyway, what I would like to do is to find the ideal vacuum pump for amateur experimenters such as us.
Here are the qualities it should have, IMHO:
(1) The pump should have at least a 3 CFM capacity; (2) It should be able to do 15u or better ultimate vacuum; (3) It should have a gas-ballast feature; (4) The intake port should be a standard pipe thread, e.g., 1/4" NPT; (5) It should have some open area around the intake port (e.g., don't need a cumbersome handle in the way), so that standard vacuum hardware can be used instead of the AC type inlet fitting; e.g, so that a standard 1/4" NPT to KF-25 adapter can be used if desired. (6) Spare parts and documentation (manuals, parts diagrams) should be available. (7) Cost should be reasonable, say less than $300.
In my opinion, the pump should not have: (1) Any kind of built in valve; (2) Any kind of built in vacuum gauge;
So far I unfortunately haven't been able to find all of these features anywhere...all in the same pump, that is.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
jpsmith123 wrote ...
If I never had the Dosivac pump, I probably wouldn't be complaining about the HF pump right now. The Dosivac took all of about 2 minutes to bury my TC gauge. Now that's performance.
Anyway, what I would like to do is to find the ideal vacuum pump for amateur experimenters such as us.
Here are the qualities it should have, IMHO:
(1) The pump should have at least a 3 CFM capacity; (2) It should be able to do 15u or better ultimate vacuum; (3) It should have a gas-ballast feature; (4) The intake port should be a standard pipe thread, e.g., 1/4" NPT; (5) It should have some open area around the intake port (e.g., don't need a cumbersome handle in the way), so that standard vacuum hardware can be used instead of the AC type inlet fitting; e.g, so that a standard 1/4" NPT to KF-25 adapter can be used if desired. (6) Spare parts and documentation (manuals, parts diagrams) should be available. (7) Cost should be reasonable, say less than $300.
In my opinion, the pump should not have: (1) Any kind of built in valve; (2) Any kind of built in vacuum gauge;
So far I unfortunately haven't been able to find all of these features anywhere...all in the same pump, that is.
I think your list is pretty good with one exception, that 15um ultimate vacuum, thats pretty low, most vacuum drying/potting electrical stuff doesnt need to be better than 100um and 50um is more than fine.
i asked these same questions in previous threads, and have found every peron and source says 50um offcially, but unofficailly 100um is almost always fine, and some told me for non-critical purposes 500um was fine for hobby stuff.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
Well if Dosivac can do it, I think others can do it too (in fact that pump did much better than its spec.).
But mainly I anticipate using it some day in electron beam experiments, so the lower the better, as far as I'm concerned.
One pump I'm looking at is this one:
It's a little on the expensive side, but if there's enough room around the intake port to adapt standard vacuum hardware (even if I have to remove the handle), I might be interested in it. I'm going to try to get more info on this pump.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
jpsmith123 wrote ...
Well if Dosivac can do it, I think others can do it too (in fact that pump did much better than its spec.).
But mainly I anticipate using it some day in electron beam experiments, so the lower the better, as far as I'm concerned.
One pump I'm looking at is this one:
It's a little on the expensive side, but if there's enough room around the intake port to adapt standard vacuum hardware (even if I have to remove the handle), I might be interested in it. I'm going to try to get more info on this pump.
yes, vacuum tubes have stringent vacuum requirements, but potting/ drying oil-- not so much.
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Harbor Freight Vacuum Pump Performance
