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In simple words, can you explain to me the Working mechanism and Basic principle of a U tube Manometer?
Is a U Tube manometer used to measure fluid pressure?

Hello Rose,

The U tube Manometer measures the difference in pressure at the 2 ends of a tube bent into the letter U. It will be more clear if you bring up a web site with an illustration of a U tube Manometer. I looked at many web sites that discussed the U-tube manometer and I was surprised how many I had to look at before finding one that I thought would work well for a simple discussion. So I am not surprised that you needed my help understanding. Use this link:

Scroll down to the section titled "U-tube manometer" with the 2 diagrams. Even this web site seems to have an error. But it is easily fixed. It seems that they got their 2 diagrams reversed in position. When it says "The diagram opposite shows a basic U-tube manometer.", they go on to say "Both ends of the tube are open". That comment refers to the 2nd diagram, which is below.

So, looking at the 2nd diagram, that is a U tube Manometer in its neutral condition. No pressure difference has been applied yet. Read the 2nd paragraph in the U tube Manometer section of the web page, remembering that it is talking about the 2nd diagram.

Now look at the 1st diagram to see how the U tube Manometer reacts when a higher pressure is applied to the left hand end of the bent tube. Note: the higher pressure is applied by connecting the top left hand end of the tube, via a hose perhaps, to an area with an unknown pressure. That is not shown to keep the diagram simple. Read the 3rd paragraph in the U tube Manometer section. As that paragraph says, the difference in the pressures at the ends of the U tube, also called Pressure differential or delta Pressure, is given by the formula
Pdif = Punk - Patm = rho*g*h
(I am spelling the Greek letter rho because of my lack of computer skills.)
Rho is the density of the liquid in the tube,
g is the acceleration due to gravity, 9.8 m/s^2,
and h, as shown in the 1st diagram, is the elevation difference between the left and right surfaces of the liquid.

Notice at the top of the 2nd page that it rearranges the formula so that if you know Patm, you can solve for the value of Punk.

I hope this helps,


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Steve Johnson


I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.


I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University

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