Both users and manufacturers expect અક્ષીય વિભાજીત કેસ પંપ to always operate at the best efficiency point (BEP). Unfortunately, due to many reasons, most pumps deviate from the BEP (or operate at partial load), but the deviation varies. For this reason, it is necessary to understand the flow phenomena under partial load.

Partial load operation

Partial load operation refers to the operating state of the pump not reaching full load (usually the design point or the best efficiency point).

Apparent phenomena of the pump under partial load

જ્યારે અક્ષીય વિભાજીત કેસ પંપ is operated at partial load, it usually occurs: internal reflow, pressure fluctuations (i.e., the so-called exciting force), increased radial force, increased vibration, and increased noise. In severe cases, performance degradation and cavitation may also occur.

Exciting force and source

Under partial load conditions, flow separation and recirculation occur in the impeller and diffuser or volute. As a result, pressure fluctuations are generated around the impeller, which generates the so-called exciting force acting on the pump rotor. In high-speed pumps, these unstable hydraulic forces usually far exceed the mechanical unbalance forces and are therefore usually the main source of vibration excitation.

The recirculation of the flow from the diffuser or volute back to the impeller and from the impeller back to the suction port causes a strong interaction between these components. This has a great influence on the stability of the head-flow curve and the excitation forces.

The fluid recirculated from the diffuser or volute also interacts with the fluid between the impeller sidewall and the casing. Therefore, it has an impact on the axial thrust and the fluid flowing through the gap, which in turn has a great influence on the dynamic performance of the pump rotor. Therefore, in order to understand the vibration of the pump rotor, the flow phenomena under partial load should be understood.

Fluid flow phenomena under partial load

As the difference between the operating condition point and the design point (usually the best efficiency point) gradually increases (shifting towards the direction of small flow), unstable fluid motion will be formed on the impeller or diffuser blades due to the unfavorable approach flow, which will lead to flow separation (de-flow) and mechanical vibration, accompanied by increased noise and cavitation. When operating at part load (i.e. low flow rates), the blade profiles show very unstable flow phenomena - the fluid cannot follow the contour of the suction side of the blades, which leads to a separation of the relative flow. The separation of the fluid boundary layer is an unstable flow process and greatly interferes with the deflection and turning of the fluid at the blade profiles, which is necessary for the head. It leads to pressure pulsations of the processed fluid in the pump flow path or components connected to the pump, vibrations and noise. In addition to the separation of the fluid boundary layer, the persistently unfavorable part load operation characteristics of the વિભાજિત કેસ pump are also affected by the instability of the external part load recirculation at the impeller inlet (inlet return flow) and the internal part load recirculation at the impeller outlet (outlet return flow). The external recirculation at the impeller inlet occurs if there is a large difference between the flow rate (underflow) and the design point. In part load conditions, the flow direction of the inlet recirculation is opposite to the main flow direction in the suction pipe - it can be detected at a distance corresponding to several suction pipe diameters in the opposite direction of the main flow. The expansion of the axial flow of the recirculation is restricted by, for example, partitions, elbows and changes in the pipe cross section. If an axial split કેસ પંપ with high head and high motor power is operated at partial load, minimum limit, or even at dead point, the high output power of the driver will be transferred to the fluid being handled, causing its temperature to rise rapidly. This in turn will lead to vaporization of the pumped medium, which will damage the pump (due to gap jamming) or even cause the pump to burst (increase in vapor pressure).

Minimum continuous stable flow rate

For the same pump, is its minimum continuous stable flow rate (or percentage of the best efficiency point flow rate) the same when it is running at fixed speed and variable speed?

The answer is yes. Because the minimum continuous stable flow rate of the axial split case pump is related to the suction specific speed, once the pump type structure size (flow-passing components) is determined, its suction specific speed is determined, and the range in which the pump can operate stably is determined (the larger the suction specific speed, the smaller the pump stable operation range), that is, the minimum continuous stable flow rate of the pump is determined. Therefore, for a pump with a certain structure size, whether it is running at fixed speed or variable speed, its minimum continuous stable flow rate (or percentage of the best efficiency point flow rate) is the same.