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The application of Appropriate Technology

Consider Worked Example 3 and Figure 16, except that in this case the control valve has been shut.

Taking the equation from Section 8 iii, we have:

P_2-P_1=\rho.g.h_1-\rho.g.h_2

We can rewrite P2 – P1 as the maximum static pressure at the valve (Pmax) and divide by ρ.g to convert this equation from pressure (Pa) to head (m) to give the maximum static head Hmax:

H_{max}=h_1-h_2

(35)

In any system the maximum static head is generally given by the difference in height from the source to the lowest point of the system.

Numerical Example

Taking the previous numerical Worked Example 3, what is the maximum static head if the tap is closed ?

Answer

Knowing h1 – h2 is 5m we can substitute this into Equation (35) to give us:

H_{max}=5

The maximum static head in the system is at the point of greatest difference in height between the source and any other point. In this case that other point is at the tap and is 5m.