Horizontal Distances – A Special Consideration

So far, we have only dealt with vertical distances, or columns of fluid and their pressures, but what about horizontal distances? The good news is that a simple application of our ∆P = ρgZ equation tells us a very important thing about pressure and horizontal distances for static fluids. We will look at this now.

Imagine a horizontal pipe full of a static fluid of density ρ, with two points of interest, 1 and 2, which are on the same horizontal level, such that the vertical distance Z1-2 between them is zero.

Figure: A horizontal pipe full of static fluid of density ρ

Figure: A horizontal pipe full of static fluid of density rho

We can apply our equation to determine what the pressure difference between points 1 and 2 might be: 

increment P subscript 1 minus 2 end subscript space equals space rho g Z subscript 1 minus 2 end subscript space equals space rho cross times g cross times 0

increment P subscript 1 minus 2 space end subscript equals space 0

We can easily see that if two points are on the same horizontal plane, and hence have no vertical distance between them, then there is no pressure difference between them, i.e. they have the same pressure. This is as appropriate within the pipeline situation shown, or for static fluid within a tank or in the atmosphere.

We have considered pressure in quite some detail and how to estimate, calculate, and manipulate pressures. Now would be a good time to look at how pressure can be measured within a brewery or a maltings.

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