Explanation diffuser pump advantages over volute pumps

The working principle of a centrifugal pump is based on the use of a rotating impeller to add energy to the working medium. In addition to increasing the static pressure, this process also increases the velocity of the fluid. By appropriately slowing down the fluid velocity, the energy increased in the form of velocity (or dynamic pressure) can be partially converted into static pressure. This is usually done by using a volute, which is a spiral shell surrounding the impeller that collects and directs the fluid to the discharge pipe while gradually reducing its speed.

The volute pump casing combines two functions: providing a hydraulic flow path for fluid and a pressure casing. In the diffusion pump, these functions are divided into two independent parts. The shell (or collector) is used to create the pressure boundary, and the speed-pressure conversion is done by using a diffuser, which is a ring with multiple diverging channels placed around the impeller. This provides more guidance for slowing down the flow, which is beneficial from multiple perspectives.

Especially for pumps operating at relatively low flow rates, the efficiency of diffusion pumps is better than that of volute pumps. In addition to the higher maximum efficiency, the efficiency will not drop rapidly when operating under partial load conditions

In addition, most of the diffusion pumps have higher head rise to off (HRTSO) and greater head curve steepness and stability, which is especially necessary for pumps operating in the API market and parallel operation

From an efficiency point of view, the diffusion pump not only has advantages. The multi-channel diffuser geometry shows more axisymmetrical properties than the asymmetric volute shape. Since this axial symmetry also exists in the pressure distribution of the flow field, most of the radial load is canceled

In addition, due to a series of diffuser blades instead of a single volute tongue, pulsation and other unstable flow phenomena from passing impeller blades are greatly reduced. Lower unstable behavior means lower vibration and noise levels, which is especially noticeable under off-design operating conditions. Reduced load and vibration in turn lead to longer average maintenance intervals, average intervals and lower minimum continuous safe flow. Although diffusion pumps are generally more expensive than volute pumps, the longer life cycle of the pump, lower spare parts costs, and a significant reduction in downtime of the entire process can easily recoup the higher investment.

Another advantage stems from the fact that the diffuser is a separate component from the pump (pressure) housing. A lot of design flexibility is introduced because a single housing can fit various diffuser geometries. Since the diffuser channels are machined, they are not limited by the casting process, as is the case with the volute casing. This also provides the opportunity to make custom diffusers for each order, which can be done very quickly. Doing this for volutes is an almost impossible task, because designing volutes is more complicated and casting models must be made and stored for each volute. This means that volute pumps are mostly a compromise: due to the limited number of volute pumps in a range, the customer's operating point will deviate from the best efficiency point of the pump. Using a diffuser can avoid this problem. By adjusting the impeller diameter and creating a customized diffuser geometry, the desired pump performance can be achieved where the best efficiency point is exactly where the customer needs it. This even provides the possibility of retrofitting existing diffusion pumps with new impellers and/or diffusers to completely change the pump's operating point and further extend the pump's life cycle.

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