Method for calculating pump shaft power

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What is pump efficiency? What is the formula? Answer: It refers to the ratio of the pump’s useful power to its shaft power. η=Pe/P The power of a pump generally refers to the input power, that is, the power transmitted from the prime mover to the pump shaft; hence it is also known as shaft power, denoted by P. 　　Effective power is equal to the product of the pump’s head, mass flow rate, and gravitational acceleration. 　　Pe=ρg QH W or Pe=γQH/1000 (KW) 　　ρ: Density of the liquid pumped by the pump (kg/m3) 　　γ: Specific weight of the liquid pumped by the pump; γ=ρg (N/m3) 　　g: Acceleration due to gravity (m/s) 　　Mass flow rate Qm=ρQ t/h or kg/s 　　I. Formula for calculating the shaft power of a centrifugal pump: 　　Flow rate × Head × 9.81 × Specific gravity of the fluid ÷ 3600 ÷ Pump efficiency 　　Unit of flow rate: cubic meters per hour 　　Unit of head: meters 　　P=2.73HQ/η, where H is the head in meters, Q is the flow rate in m3/h, and η is the pump efficiency. P represents the shaft power in KW. In other words, the shaft power of the pump is P=ρgQH/1000η (kW), with ρ=1000 Kg/m3 and g=9.8. 　　The unit of specific gravity is Kg/m3, the unit of flow rate is m3/h, and the unit of head is meters. 1 Kg equals 9.8 Newtons. 　　Therefore, P=Specific gravity * Flow rate * Head * 9.8 Newtons/Kg 　　= Kg/m3 * m3/h * m * 9.8 Newtons/Kg 　　= 9.8 Newtons * m / 3600 seconds 　　= Newtons * m / 367 seconds 　　= Watts / 367 　　The above explanation clarifies the origins of the units. The formula above is used to calculate the power required for water; the shaft power is then obtained by dividing this value by the efficiency. 　　Let Ne be the shaft power, P be the motor power, and K be a coefficient (the reciprocal of efficiency). 　　Motor power P=Ne*K (K takes different values depending on Ne; see the table below) 　　Ne≤22: K=1.25 　　22 < Ne ≤ 55: … 　　II. Formula for calculating the shaft power of a slurry pump: 　　Flow rate Q: m3/h 　　Head H: meters of water 　　Efficiency n: % 　　Density of the slurry A: Kg/m3 　　Shaft power N: KW 　　N=H*Q*A*g/(n*3600) 　　The motor power also needs to take into account the transmission efficiency and safety factors. Generally, 1 is used for direct connection, 0.96 for belt drive, with a safety factor of 1.2. III. Pump efficiency and its calculation formula: It refers to the ratio of the pump’s effective power to its shaft power. η=Pe/P The power of a pump generally refers to the input power, that is, the power transmitted from the prime mover to the pump shaft; hence it is also known as shaft power, denoted by P. 　　Effective power is equal to the product of the pump’s head, mass flow rate, and gravitational acceleration. 　　Pe=ρg QH (W) or Pe=γQH/1000 (KW). ρ: the density of the liquid pumped by the pump (kg/m3); γ: the specific weight of the liquid pumped by the pump, γ=ρg (N/m3); g: the acceleration due to gravity (m/s). Mass flow rate: Qm=ρQ (t/h or kg/s). IV. Estimating the power of household pumps using empirical methods: For household use, the minimum power is 370W, while the maximum generally does not exceed 5.5 KW. One can use a flashlight or a chandelier to determine the size of the pump, and then estimate its power level. V. To estimate the power of a well pump, an approximate calculation can be made using electrical measurements. Power can be determined by measuring the current with a clamp meter; power is then calculated by multiplying the current by the voltage and by the power factor (WeChat official account: Pump Butler). A power factor of 0.8 can be assumed to obtain the actual operating power. If water is being pumped up, a load capacity of 70% can be considered, and dividing this value by 0.8 gives the rated power of the motor. It is also possible to turn off the water valve or similar, and let the motor drive the pump at no load. In this case, the current is likely to be no more than 40% of the rated current. By measuring the current, the power can be calculated; then dividing this value by 0.4 gives the motor’s power. By comparing this figure with the previous one, it is possible to determine whether there is any error in the calculated motor power. The distance between the pump and the ground can be measured; by knowing the height to which water is pumped, the head pressure can be determined. Next, use a bucket to see how much water is pumped up in 1 minute, measure the volume of that water, and calculate the flow rate accordingly. With both the head pressure and the flow rate, it is also possible to calculate the power. Head * flow rate ÷ 367.02 ÷ 1.2; taking into account the pump’s efficiency of 0.7 and dividing by 0.7 gives an approximate value for the motor power. Pumps and motors that operate in humid environments for extended periods of time may experience leakage issues; there can be variations in current flow, and the bearings and pipelines might have problems as well. The power output can also vary significantly. The methods mentioned above can only serve as a reference – it is actually better to go down into the pit to carry out repairs, as equipment needs to be inspected regularly.