Reasons for low efficiency of centrifugal pump

Centrifugal pump is one of the main equipment for liquid transportation, which is widely used in various industries of industrial and agricultural production and people's daily lives. Its electricity consumption accounts for more than 30% of the total electricity consumption of enterprises. According to on-site investigation, the actual operating efficiency of centrifugal pumps is currently low and energy consumption is excessive, causing undue losses to the enterprise.

1. The operating conditions of the centrifugal pump deviate from the design conditions, resulting in low efficiency

The working parameters of a centrifugal pump include speed n, field range H, flow rate qv, and efficiency. When the head of the centrifugal pump changes, other parameters also change accordingly. The centrifugal pump has the highest operating efficiency under design conditions. When using a centrifugal pump with a high head or a large flow rate, deviating the operating conditions from the design conditions can result in low efficiency.

2. Various losses inside the centrifugal pump cause a decrease in the operating efficiency of the centrifugal pump

The losses caused by liquid flowing through the impeller include mechanical losses, flow losses, and leakage losses. Correspondingly, the efficiency of centrifugal pumps is divided into mechanical efficiency, hydraulic efficiency, and volumetric efficiency. Mechanical losses include wheel resistance losses caused by friction between the impeller cover and the outer side of the disc with the liquid, as well as friction losses in the bearings and packing box; Leakage losses include leakage losses at the impeller sealing ring, between stages, and at the axial force balancing mechanism; Flow losses are caused by frictional losses along the flow path of liquid through impellers, volutes, and diffusers, as well as local resistance losses that flow through the aforementioned locations, including impact losses generated when fluid flows into the blade channel and energy conversion device. The majority of these losses are converted into heat absorbed by the fluid.

It can be seen that in order to improve the efficiency of centrifugal pumps, mechanical losses, volume losses, and hydraulic losses should be reduced from various aspects.

3. Low pipeline efficiency

When the flow rate or head of the conveyed liquid changes, a common method is to adjust the valve. Although this method is convenient, it causes significant resistance loss in the pipeline, resulting in the centrifugal pump operating at low efficiency.

4. Low efficiency of centrifugal pump itself

To ensure high operating efficiency of centrifugal pumps, high-efficiency centrifugal pumps should be selected first. For example, segmented multi-stage centrifugal pumps have higher efficiency, while IS type single-stage single suction centrifugal pumps have lower efficiency. However, due to the poor quality of maintenance and installation, mechanical losses, hydraulic losses, and volume losses have increased, resulting in the high-efficiency centrifugal pump not playing its due role, causing the high-efficiency pump to operate in a low efficiency state. In addition, when choosing a centrifugal pump, it is often based on the maximum flow rate and head while considering a certain margin, resulting in the phenomenon of a large horse pulling a small car, which cannot achieve the goal of minimizing energy consumption as much as possible.

The actual operating efficiency of a centrifugal pump is the main indicator for determining whether the operation of the centrifugal pump is economical. Reasonable selection of centrifugal pumps to ensure efficient operation is of great significance.