Machinery's Handbook, 31st Edition
2798 HEAD For water at 70°F (20°C), head and pressure equivalents can be found in Table 30 and Table 31. Table 30. Pressure in Pounds per Square Inch for Different Heads of Water Head, ft 0 1 2 3 4 5 6 7 8 9 0 … 0.43 0.87 1.30 1.73 2.16 2.60 3.03 3.46 3.90 10 4.33 4.76 5.20 5.63 6.06 6.49 6.93 7.36 7.79 8.23 20 8.66 9.09 9.53 9.96 10.39 10.82 11.26 11.69 12.12 12.56 30 12.99 13.42 13.86 14.29 14.72 15.15 15.59 16.02 16.45 16.89 40 17.32 17.75 18.19 18.62 19.05 19.48 19.92 20.35 20.78 21.22 50 21.65 22.08 22.52 22.95 23.38 23.81 24.25 24.68 25.11 25.55 60 25.98 26.41 26.85 27.28 27.71 28.14 28.58 29.01 29.44 29.88 70 30.31 30.74 31.18 31.61 32.04 32.47 32.91 33.34 33.77 34.21 80 34.64 35.07 35.51 35.94 36.37 36.80 37.24 37.67 38.10 38.54 90 38.97 39.40 39.84 40.27 40.70 41.13 41.57 42.00 42.43 42.87 Table 31. Heads of Water in Feet Corresponding to Certain Pressures in Pounds per Square Inch Pressure, lb/in 2 0 1 2 3 4 5 6 7 8 9 0 … 2.3 4.6 6.9 9.2 11.5 13.9 16.2 18.5 20.8 10 23.1 25.4 27.7 30.0 32.3 34.6 36.9 39.3 41.6 43.9 20 46.2 48.5 50.8 53.1 55.4 57.7 60.0 62.4 64.7 67.0 30 69.3 71.6 73.9 76.2 78.5 80.8 83.1 85.4 87.8 90.1 40 92.4 94.7 97.0 99.3 101.6 103.9 106.2 108.5 110.8 113.2 50 115.5 117.8 120.1 122.4 124.7 127.0 129.3 131.6 133.9 136.3 60 138.6 140.9 143.2 145.5 147.8 150.1 152.4 154.7 157.0 159.3 70 161.7 164.0 166.3 168.6 170.9 173.2 175.5 177.8 180.1 182.4 80 184.8 187.1 189.4 191.7 194.0 196.3 198.6 200.9 203.2 205.5 90 207.9 210.2 212.5 214.8 217.1 219.4 221.7 224.0 226.3 228.6 Bernoulli’s equation is commonly used in the design of hydraulic systems. In terms of head, it takes the following form. This equation assumes steady flow, so additional terms are used in cases of pulsating flow as with reciprocating pumps. h 1 h 2 h L = + or z 1 v 1 2 z 2 v 2 2 p 2 γ --- h L = + + + where h L is minor loss of head due to viscous and turbulent shear stresses and other fac- tors. The terms of this equation are explored further in this section. Elevation Head: This is the vertical distance between the point of concern and the free surface of the fluid. This head is considered positive if the free surface is above the point of concern, and negative if the point of concern is above the free surface. No equation is required. When applied to a suction line, when the pump is above the fluid free surface (negative head) this is often referred to as “suction lift.” Elevation head is often repre - sented by the letter z or as h z . Pressure Head: The equivalent head imparted by the pressure applied to the fluid at its free surface. This is calculated using the following equation: h p p γ = -- where p is applied absolute pressure and g is specific weight. 2 g --- p 1 γ --- + + 2 g ---
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