## Liquid PumpsTechnical Equations and Information Tables

Efficiency Formulas for Rotary Positive Displacement Pumps    Rules of Thumb for Motors
Approximate rpm at Full Load for Medium Sized Motors
Atmospheric Pressure Conversion
Loss of Air Pressure Due to Friction
Loss of Air Pressure Due to Pipe Bends
Flow of Air through Orifice

Efficiency Formulas for Rotary Positive Displacement Pumps

 Liquid HP = GPM x psi1747

 Volumetricefficiency = Actual GPMTheoretical GPM

 Overall pumpefficiency = HP of fluid dischargeHP of driving motor

 Mechanicalefficiency = Overall pump efficiencyVolumetric efficiency

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Pipe Velocity

 Velocity(ft/sec) = GPM x 0.321     (pipe ID in inches)2

• It is best to allow 10 pipe diameter upstream and 5 pipe diameter downstream leading to the pump suction.
• Try to keep pipe velocities around 10 ft/sec for good practical results.
• Doubling the pipe diameter increases the capacity of the pipe four times.

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Rules of Thumb for Motors

At 3600 rpm: motor develops 1.5 ft/lb per hp

At 1800 rpm: motor develops 3.0 ft/lb per hp

At 1200 rpm: motor develops 4.5 ft/lb per hp

At 575 volts, a 3-phase motor draws 1.00 amps per hp

At 460 volts, a 3-phase motor draws 1.25 amps per hp

At 230 volts, a 3-phase motor draws 2.50 amps per hp

 hp = Torque ft/lb x rpm5252

 Torque (ft/lb) = hp x 5252rpm

 Torque (in/lb) = hp x 63,025rpm

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Approximate rpm at Full Load for Medium Sized Motors

 Poles rpm60 Hz Synchspeed rpm50 Hz Synchspeed 2 3500 3600 2850 3000 4 1750 1800 1450 1500 6 1150 1200 950 1000 8 850 900 700 750

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Atmospheric Pressure Conversion

 Altitudein feet Pressurein psia Altitudein feet Pressurein psia 0 14.7 5000 12.23 100 14.64 7000 11.34 300 14.54 10,000 10.11 500 14.43 15,000 8.29 700 14.33 20,000 6.76 1000 14.17 25,000 5.45 1500 13.92 30,000 4.36 2000 13.66 40,000 2.72 3000 13.17 50,000 1.68 4000 12.69 60,000 1.04

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Loss of Air Pressure Due to Friction
(Per 100 Feet of Pipe, 100 psi Initial Pressure)

 Free-aircapacity in cfm(at 14.7 psi) Equivalentcapacity in cfm(at 100 + 14.7 psi) Loss of pressure in psi per pipe ID 1/2" 3/4" 1" 1-1/4" 1-1/2" 2" 10 1.28 1.38 0.09 0.03 0.007 20 2.56 1.42 0.34 0.10 0.026 0.012 30 3.84 3.13 0.74 0.23 0.056 0.026 40 5.13 5.55 1.28 0.38 0.096 0.044 0.013 50 6.41 8.65 2.00 0.60 0.146 0.067 0.020 60 7.69 2.84 0.84 0.210 0.095 0.027 70 8.97 3.85 1.12 0.280 0.130 0.036 80 10.25 5.01 1.44 0.360 0.160 0.046 90 11.53 6.40 1.85 0.450 0.200 0.058 100 12.82 7.80 2.21 0.550 0.250 0.069 125 16.02 12.40 3.41 0.850 0.380 0.107 150 19.22 18.10 4.91 1.200 0.540 0.150 175 22.43 6.80 1.640 0.730 0.200 200 25.63 8.79 2.120 0.950 0.260 250 32.04 3.300 1.480 0.400 300 38.45 4.710 2.100 0.570 350 44.86 6.450 2.860 0.770 400 51.26 8.300 3.700 0.990 450 57.67 4.650 1.270 500 64.08 5.790 1.560 600 76.90 8.45 2.230 700 89.71 3.000 800 102.50 4.000 900 115.30 5.050 1000 128.20 6.200

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Loss of Air Pressure Due to Pipe Bends
(Per 100 Feet of Straight Pipe)

 Angle ofpipe bend Loss of pressure in psi per pipe ID 1/2" 3/4" 1" 1-1/4" 1-1/2" 2" 45° 0.73 0.92 1.18 1.55 1.85 2.35 90° 1.60 2.00 2.50 3.40 4.00 5.10

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Flow of Air through Orifice
(with Discharge of Orifice at 14.7 psia and 70°F)

 Supplypressure(psig) Flow of air in cfm per orifice size 1/32" 1/16" 3/32" 1/8" 5/32" 3/16" 7/32" 1/4" 9/32" 5/16" 65 1.15 4.49 10.10 17.90 27.90 40.30 55.20 71.80 89.90 111.70 70 1.21 4.77 10.80 19.10 29.70 42.80 58.80 76.40 95.70 118.80 75 1.30 5.06 11.40 20.20 31.50 45.40 62.30 81.00 105.50 126.00 80 1.37 5.35 12.10 21.10 33.30 48.00 65.80 85.60 107.40 133.10 85 1.44 5.64 12.70 22.50 35.10 50.60 69.40 90.30 113.20 140.30 90 1.52 5.92 13.40 23.70 36.90 53.20 72.90 94.80 119.00 147.50 95 1.59 6.21 14.00 24.80 38.70 55.70 76.50 99.40 124.90 154.60 100 1.66 6.50 14.70 26.00 40.50 58.30 80.00 104.60 130.70 161.80 125 2.03 7.94 17.90 31.70 49.50 71.40 97.78 127.10 159.80 197.50 150 2.40 9.28 21.20 37.50 58.40 84.40 115.40 150.40 189.00 233.30

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