Effect of high pump inlet pressure on shaft power
Thread Content
The effect of high pump inlet pressure on shaft power. An 800-cubic-meter storage tank filled with water, equipped with 3 pumps of 60 m³/h capacity, a head of 75 meters, 22 KW power rating, and 2950 rpm speed. The tank’s height is 13 meters, and its rated current is 40 A. During operation, the system often shuts down due to excessive current; the on-site technicians believe this is caused by high inlet pressure. He said to optimize the impeller without affecting flow rate and head. However, once the impeller is formed, its performance is fixed; according to the cutting law, the head and flow rate will definitely change. Let’s mainly discuss: 1. The impact of high pump inlet pressure on pump power. 2. Impact on pump head. (The impact on axial force and sealing is not discussed.)
Ignoring the axial force has no effect on power. Head is determined by the rotational speed and the impeller diameter; if these parameters remain unchanged, then the head also remains unchanged.
During performance tests in their factory, the pumps worked normally, but they kept shutting down once they were installed on site. Add reducer fittings to the pump inlet pipeline to introduce one additional size, and add another size at the outlet for concentricity. The pump is directly connected to the motor, is horizontal in design, and features a mechanical seal. There are no leaks during operation; the motor temperature is normal, and the bearings are in good condition. How much impact does axial force have on power?
I encountered the same problem as well: once the pump started running, the outlet valve would trip
Dalian Sulzer ZE150-3250: flow rate of 363 m3/h, head of 67 m, speed of 2970 r/min. The flow rate at the outlet is low while the pressure is high; the machine shuts down when the outlet valve is opened wider. What could be the reason?
In this case, there are more electrical factors at play, including the set value of the rated current, electrical wiring, and insufficient motor output. Another issue is that the efficiency rating of the pump is inflated, requiring a higher shaft power. If there are no strict requirements regarding flow rate, just turn the impeller.
High inlet pressure can affect the axial force and thus the shaft power, but it does not affect the head. Check whether the excessive axial force is the cause of the high shaft power, which leads to the motor stopping； It is still the competition for flow rate among the three pumps that results in excessive shaft power for one of the pumps. It was still the case that the margin of motor power chosen during the initial selection was too small, preventing it from operating at high flow rates. Or both
If the efficiency is 72%, the motor power is 110 KW. Please provide detailed parameters such as efficiency, motor power, medium density, and actual operating conditions; it would be best to have the manufacturer’s selection chart as well
If axial force is not considered, there is no impact; axial force will cause the frictional work to increase
Please send the manufacturer’s label along with the possible reasons. 1. The inlet pressure has changed by 1.3 BAR; the frictional loss should not change that much. The most likely explanation is that the actual efficiency differs significantly from the efficiency indicated on the expected curve. This is closely related to the manufacturer’s manufacturing standards