Page 2 of 3

Re: Update on experiment

Posted: Sat Mar 14, 2020 3:20 am
by Rich Feldman
You can look up the conversion from pascals to whatever unit is indicated by your gauge.

One strong lesson from the first page of vacuum FAQs here:
The pressure "rating" of a rotary vacuum pump, even brand new, is generally very very optimistic. See FAQ for the reasons.

What happens when you connect gauge directly to pump with nothing else?
You must have tried that before bringing chamber into the picture!

Re: Update on experiment

Posted: Sat Mar 14, 2020 6:03 am
by steventw
Actually haven’t Tryed that... guess could give it a go
Will try gauge to pump in a little while

Well the fancy gauge was a recent addition
When relised the gauge that came with it couldn’t go past -30hg

Re: Update on experiment

Posted: Sat Mar 14, 2020 11:00 am
by steventw
Ok got to about 0.2500 mbar

Re: Update on experiment

Posted: Sat Mar 14, 2020 5:11 pm
by Mark Rowley
We normally use mTorr or Microns for scientific vacuum work and I believe your electronic meter can toggle to those measurement units. If not, using an online conversion tool would be a good idea.

So that's around 188 mTorr which is still not good......better, but not good, especially if the measurement is taken at the pump. You should be able to attain at least 15 mTorr (0.020mBar). If your connection point to the gauge is sound, then you definitely have some pump issues.

Mark Rowley

Re: Update on experiment

Posted: Sat Mar 14, 2020 6:24 pm
by Richard Hull
Mark is correct, but even with a perfect pump, the connections and the chamber are usually the killers where all of the real leaks are to be found. The general rule is that with 10 microns at the pump entrance, (the head), You will never get that in any chamber unless it is tiny and connected directly to the pump. Anything in the chamber like insulated wire, plastics of any type, etc., will forever ruin the vacuum especially if there is any form of discharge taking place.

Richard Hull

Re: Update on experiment

Posted: Fri Mar 20, 2020 7:44 am
by steventw
Ok thanks for advice guys

I have a bit of cash saved in joint account with mum
I’m thinking if I can talk her into letting me spend some would this pump be worth it

https://hvacdirect.com.au/vector-rd-160 ... cuum-pump/

Any advice or suggestions would be welcome

Re: Update on experiment

Posted: Fri Mar 20, 2020 9:13 am
by ian_krase
I am honestly a bit skeptical of that pump -- not that its a bad pump, but that there are probably better ones for a lower price.

Re: Update on experiment

Posted: Fri Mar 20, 2020 4:30 pm
by Rich Feldman
Not so fast, Steven.

Today you get 4.9 mbar in the chamber, and 0.25 mbar with gauge on pump with nothing else. (Even in the second case you might be suffering from a connector leak or old vacuum pump oil.)

So as Richard said a couple posts up,
the vast majority of your unwanted pressure in chamber comes from leaks, in combination with vacuum hose too long and too narrow.
If you put God's own vacuum pump in place of yours, the reduction in chamber pressure would be inconsequential.

You and your mum's money would be much better spent dealing with the leaks, and getting a fatter hose for the pump you got.
Plenty of hints have been given in this very thread, not to mention all the FAQ's.
Call back when you can demonstrate chamber pressure less than 0.5 mbar.

Re: Update on experiment

Posted: Fri Mar 27, 2020 2:35 am
by steventw
Did best I can to sort any leaks
Left pump running for 2 and half hours and made it down to 661 - 665 micron
Seems to be hovering between
It is a relatively cheap pump that came with chamber.
Did some looking and is rated to 25 micron apparently.
But I doubt that’s taking into account the 15 gallon chamber I’m using could be part of issue having to move so much volume.

Re: Update on experiment

Posted: Tue Mar 31, 2020 10:50 am
by Dennis P Brown
Glad your still working towards your goal. That shows commitment; however, with vacuum systems and leaks, one must also accept that there is a reason people use professional chambers, connections and vacuum pumps - saves vast amounts of time and efforts while finally allowing one to reach their desired vacuum conditions.

I have obtained very professional equipment via ebay and secondary sellers - these can very inexpensive if one waits and watches what is available - I obtained two multi-thousand dollar pumps for a few bucks - shipping was the real expense ($30 each.) Ditto on good (i.e. working) micron gauges and vacuum piping/connectors. I obtained a large vacuum shell that needed a 8 inch window - I simply bought a telescope glass blank, inexpensive glass drills and made a high voltage feed thru that was vacuum tight. Work arounds exist and can be done cheaply if one is clever.

Hope you succeed and obtain your end goals but creating micron grade vacuum systems is not easy to do without proper equipment - just no easy work-arounds.