Introduction to Manometers: Two Essential Rules

Dr. Faith Morrison shows how you can solve any manometer problem with just two rules: 1) pressure is equal at equal elevations in the same fluid and 2) pressure at the bottom of a column of fluid equals pressure at the top plus rho*g*h. For handout go to www.chem.mtu.edu/%7Efmorriso/cm4650/movies.html

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Education

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• manometers
• hydrostatics
• CM3215
• Michigan
• Tech

[DrMorrisonMTU]

If I understand your question correctly, you have the b-side open to air (and the pressure at the top is Patm) and the a-side open to some other pressure Pa. If you do it my way, you get rho*g*h+Patm=Pa. In this case Pa is the absolute pressure. If you do it your tutor's way and say the pressure at the top is zero (gauge pressure), then you get rho*g*h=Pa but now Pa is in gauge pressure. In typical gauges, they read zero when open to atmosphere.

[divinenuker]

Its a good basic explanation.. but if the manometer problem is really complicated.

Where you have multiple (Jump Across Points) P1 = P2

P3=P4 , P5=P6 , and the some "Jump Across Points" are on the top so the "column" is actually inverted.

In the end if you want the pressure difference between the entry and the exit.. how would you add them together using your method. I can't figure it out. It gets messy

[DrMorrisonMTU]

Hi, for the complex case you cite, you need to choose "jump across points" that are in the same fluid and not at the top, but at the bottom. Always remember that the pressure is the same in the same continuous fluid at the same elevation. I will try to post a video on this. Dr. Morrison

[c10seth]

my fluids professor could take a lesson from you b/c that 5 min video made more sense than most of my semester. Good job.

[strongwiller]

thanx. now i can get my chemical engineering degree. very helpful vid =)

[moviericky]

Oh my goodness...You're left handed!

[frahs993]

shouldn't it be volume, not height?

[Dinty51]

@c10seth two days before my first fluids test and those are my exact thoughts!!!!!!

[itsd4real]

Dr. Morrison can you please do a mor complicated manometer where there's more than 2 arms and more than 2 liquids with different density an with both ends of the manometer closed. Thank you

[MattSpon]

@MattSpon Haha! My bad... that was king crimson playing on my itunes! lol wow and I'm in the health sciences... look out.

[MattSpon]

good vid! the guitar was WAY too overbearing for my ears.

[jimmertzis]

so basically PA-PB=ρg*g*h1?

[NuclearDispute]

For those of us who are familiar with tranposition and the fact that rho is the density of the substance, i.e. water = 1000, I dont think it was clearly explained what rho meant in your video? Presumably a certain amount of this you are expecting your viewers to understand, for instance g - gravity - 9.81 m/s^2 ?