Understand the technical characteristics and power calculation methods of pump motors in one article

The height of the center of the horizontal pump shaft and the motor shaft is unequal, and the scale deposition in the vertical pump body or the sinking of the rotating shaft will cause the motor to overcurrent operation. Troubleshooting can be done from the following aspects. The pump absorbs impurities such as sediment and rust particles to increase the resistance of the medium, resulting in the load being detachable to remove the impurities in the pump, and at the same time, attention should be paid to the cleaning of the water inlet filter, the pump runs for a long time or due to poor assembly, the gap between the impeller and the pump casing is too small, and friction occurs during operation; or the packing is pressed too tightly, and no water enters the stuffing box; In addition, the gap between the pump coupling and the motor coupling is too small, and the two shafts are on top of each other during operation, which increases the consumption of shaft power.

First, it can be disassembled and inspected to repair each part with the size; Second, the packing gland should be relaxed, and the cleaning water seal pipe should be checked; Third, adjust the clearance between couplings, and it is generally believed that the clearance should be around Smm. If the water flow rate of the pump is too large and the motor is overloaded, the small valve opening can be closed to reduce the flow.

The formula for calculating the power of the pump motor is as follows, with an explanation of the meaning contained in each part of the formula.

N=KP=KPe/η=KρgQH/1000η (KW)

The symbols in the formula are as follows:

P: The shaft power of the pump (KW), also known as the input power, that is, the power transmitted by the motor to the pump shaft;

Pe: effective power of the pump (KW). It is also called output power, that is, the effective energy obtained from the pump by the output medium per unit time;

ρ: the density of the medium conveyed by the pump (Kg/m³). Generally, the density of water is 1000Kg/^m3 (specific gravity is 1), and the density of acid is 1250Kg/^m3 (specific gravity is 1.25);

Q: Flow rate of the pump (^m3/s). When the flow unit is m³/h, it should be converted to m³/s;

H: head of the pump (m);

g: acceleration due to gravity (m/s²), which is 9.8 m/s²;

K: The safety factor of the motor, generally 1.1~1.3;

η: the efficiency of the pump. The attached table shows the efficiency values of the four main operating points of the UHB series pump (some of which may coincide), and the flow rate --- efficiency curve can be estimated according to the data of these four points. When calculating, the efficiency is roughly taken in the curve according to the flow rate.

For example, a user needs to use 50UHB-ZK-25-35 pump, Q=^25m3/h, H=35m, medium density ρ=1250Kg/^m3, speed n=2900r/min, please choose a motor.

Solution: According to the data provided in the attached table, the efficiency of the 50UHB-ZK-25-35 pump at 25m³/h is 52%, and the data are substituted into the formula:

N=KρgQH/1000η=1.2×1250×9.8×25×35/(1000×0.52×3600)=6.9KW