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2 questions regarding vacuum pump

2 questions regarding vacuum pump

2 questions regarding vacuum pump

(OP)
First im having an issue with my manometer. I have a controlled leak valve on my rotary vacuum pump setup to controll how much vacuum it pulls. By logic as i close the valve my manometer should read lower torr, but instead it goes up. My manometer has a positive and negative pressure connection like the one in this picture http://cfnewsads.thomasnet.com/images/large/583/58... . But the manual that came with mine did not say which was positive and which was negative so i tried to get readings with both sides but each side had the same issue, and the vacuum increased the torr increased which shouldnt happen.

The second question is a quick one, can i leave clean vacuum oil in the pump?

RE: 2 questions regarding vacuum pump

Your manometer is reading gage pressure not absolute pressure. Gage pressure is the difference from atmospheric reference pressure. If you lessen the air leak into the vacuum you will get a lower absolute pressure but the gage pressure reading will go up. Take the time to understand how your instrument works.

RE: 2 questions regarding vacuum pump

(OP)
Ive tried can seem to find any manuals online for one like mine.If its reading gage pressure could i not just subtract the reading from atmospheric to get the absolute pressure?

RE: 2 questions regarding vacuum pump

Yes, you could. But, you can't know the actual atmospheric pressure without a barometer, which is itself an absolute pressure gage. Closed-end mercury manometers used to be the most common instrument for reading vacuum. With one end closed and filled completely with mercury, it created a zero absolute pressure reference.

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