Author Topic: manometer problem  (Read 707 times)

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zero_nrg

  • Guest
manometer problem
« on: September 13, 2003, 11:37:00 PM »
I have a recently acquired mercury manometer which, I have read, is commonly referred to as a "stick" manometer.  It is a Pyrex model 6952 and has an glass inner tube (gets filled with Hg) that fits into an outer (partially filled) graduated (mm) glass tube.    I followed the filling instructions to a tee: attatch rubber tube to inner tube, pour in Hg, tap to get Hg into inner tube, heat inner tube gently to remove air (with filling tube still attatched) etc.  I don't have any instructions for the use of this manometer, but according to Zubrick the level of the outer tube is subtracted from the level of the inner tube.  The problem I have is that when I take a vacuum reading with it the level in the inner tube goes below the level in the outer tube (just slightly- maybe 1mm).  Zubrick says there must be air in the inner tube.  So I repeat the filling procedure but pretty much get the same reading.  Am I not heating the inner glass tube enough to remove any trapped air?  I tried to heat it just enough so as not to start to melt the silicone rubber filling tube attatched to the end.  Any ideas anyone has are appreciated.  -Zero

terbium

  • Guest
Filling a stick manometer.
« Reply #1 on: September 14, 2003, 05:59:00 AM »
As I remember: After filling it as best as possible via the rubber tube you then remove the rubber tube and place the stick, opening down, extending a short distance into a pool of mercury then you heat the rest of the stick with a gas flame.


calcium

  • Guest
pour out some Hg
« Reply #2 on: September 14, 2003, 03:25:00 PM »
You just put a little too much mercury in the outer tube.

terbium

  • Guest
Absolute pressure.
« Reply #3 on: September 14, 2003, 11:28:00 PM »
You just put a little too much mercury in the outer tube.
No, this is not the problem. It does not matter how much mercury is in the outer tube. This device is measuring an absolute pressure as indicated by the height of the inner mercury column above the outer mercury reservoir.