Shaft power of centrifugal pump

Effective power of the pump: Pe=γQH. The formula for calculating the shaft power of a pump is relatively complex, and it is approximately equal to the output power of the drive motor.

Effective power refers to the effective energy obtained by the liquid pumped out per unit of time from the pump. P=ρQgH, where P is the useful power, in W ； ρ is the liquid density, kg/m3 ； Q is the volumetric flow rate, in m3/s ； H is the head, in m ； g is the acceleration due to gravity, in m/s2. The shaft power of the pump is the useful power multiplied by the transmission coefficient.

What is the transmission coefficient, and what is its typical value?

Shaft power is equal to useful power divided by the pump’s efficiency.

The formula for calculating the shaft power of a pump is: N = pQH / (102 × n1 × n2). Where: N represents power, in Kw; p is the density, in kg/m3; Q is the flow rate, in m3/s; n1 is the efficiency of the pump, usually 0.85; n2 is the transmission efficiency, which is 1 for direct connection

Sorry, I missed one: H, head lift, in meters

The formula for calculating the shaft power of a pump is: N = pQH / (102 × n1 × n2). In this formula, N represents power in kW; p is the density in kg/m3; Q is the flow rate in m3/s; n1 is the efficiency of the pump, usually 0.85; and n2 is the transmission efficiency, which is 1 for direct coupling. In the formula, does the denominator 102 refer to 10 squared or 102? Thank you!

1. The efficiency generally does not reach 85%; 2. The denominator in the formula is 102.

The efficiency indicated by the manufacturer is 0.85, but in reality some pumps only achieve 60% efficiency.

Shaft power (input power) (P) – The power transmitted to the pump shaft from the prime mover is known as shaft power, denoted by P, with the unit being KW. On the pump’s nameplate, this value represents the shaft power, that is, the rated power. ================================ Effective power (output power) – the work done by the water pump on the liquid per unit of time, denoted as Pe. Pe=ρgQH (W) where ρ is the liquid density (kg/m3), g is the acceleration due to gravity (m/s2), Q is the volumetric flow rate (m3/s), and H is the pressure head (m). Additionally, γ represents the specific weight of the liquid pumped by the pump, with γ=ρg (N/m3). =============================== Efficiency is the ratio of the effective power output by the water pump to its shaft power, expressed as η. Output power (W) x 1000 / Shaft power (KW) x 100% Last edited by x850xtpe on 2008-2-3 19:37]

In fact, once the flow rate Q, the pump pressure P, and the efficiency η are known, it is possible to calculate the useful power and the shaft power; the useful power is P = Q * P, while the shaft power Pe is P / η

In the formulas mentioned above, what is calculated is the net power. When using a motor or other driving devices, it is necessary to take a coefficient into account, with different coefficients being required for different powers. Furthermore, in the aforementioned formula, the most important factor is the efficiency of the pump; the efficiency of pumps of different types and working with different media varies! Special attention.

Formula for calculating the shaft power of a water pump: (1) For centrifugal pumps, Shaft Power = Flow Rate × Head × 9.81 × Specific gravity of the fluid ÷ 3600 ÷ Pump efficiency. The unit of flow rate is cubic meters per hour, and the unit of head is meters. P = 2.73HQ/η, where H represents the head in meters, Q represents the flow rate in m3/h, and η represents the pump’s efficiency. P represents the shaft power in KW. In other words, the shaft power of a pump is given by P = ρgQH/1000η (in KW), where 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; this formula is used to calculate the power required by the pump. The shaft power can be obtained by dividing this value by the pump’s efficiency. Let Ne represent the shaft power, P represent the motor power, and K represent a coefficient (the reciprocal of the efficiency). Motor power P = Ne × K. The value of K varies depending on the value of Ne, as shown in the table below: If Ne ≤ 22, then K = 1.25

The shaft power should be the effective power divided by the efficiency, which is what you refer to as the transmission coefficient