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Old 09-20-2019, 12:03 PM   #1
MT BUICKNUT
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Default Vacuum pump ins" VS lbs.

On a vacuum pump my gauge reads lbs. then I read about inches of mercury. What's the difference, and what would be a suitable setting in pounds?
Thanks Rick
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Old 09-20-2019, 01:03 PM   #2
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Default Re: Vacuum pump ins" VS lbs.

1" Hg is about -.5 psi. If your gauge is reading -10 psi, you have about 20" Hg
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Old 09-20-2019, 07:42 PM   #3
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Default Re: Vacuum pump ins" VS lbs.

Hey Bill!!
Question I've been thinking about:
How does vacuum change as altitude increases? If I run 8 inches at sea level and I take my car to Santa Fe, elevation 7,000 msl, what does my vac gauge read? Is there a formula, does it go down 2%/1000 feet or ???? Lower than 6?
thx!!
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Old 09-21-2019, 03:09 PM   #4
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Default Re: Vacuum pump ins" VS lbs.

I'm not sure. I do know that It's harder to get good vacuum at high altitude
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Old 09-21-2019, 05:20 PM   #5
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Default Re: Vacuum pump ins" VS lbs.

https://www.engineeringtoolbox.com/a...ure-d_462.html

Look at the PSIA at different elevations. 14.7# PSIA is what would be considered normal for sea level, or 0# PSIG.
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Old 09-21-2019, 08:37 PM   #6
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Default Re: Vacuum pump ins" VS lbs.

Quote:
Originally Posted by NHRA686 View Post
I'm not sure. I do know that It's harder to get good vacuum at high altitude

LOL that's because the pressure you are evacuating is less--atmospheric pressure. Previous poster is right. It's about a 50% ratio "roughly" psi to inches Hg. Sea level is just under 15psi in rough figures, and just under 30" Hg. I refuse to think in "bars." And be careful, somethings are inches of WATER. We used to use that all the time in HVAC for gas/ LP pressure, and duct pressure
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