XI Международная студенческая научная конференция Студенческий научный форум - 2019

The centrifugal pump is the most used pump type in the world. The principle is simple, well-described and thoroughly tested, and the pump is robust, effective and relatively inexpensive to produce. There is a wide range of variations based on the principle of the centrifugal pump and consisting of the same basic hydraulic parts. The majority of pumps produced by Grundfos are centrifugal pumps.

An increase in the fluid pressure from the pump inlet to its outlet is created when the pump is in operation. This pressure difference drives the fluid through the system or plant.

The centrifugal pump creates an increase in pressure by transferring mechanical energy from the motor to the fluid through the rotating impeller. The fluid flows from the inlet to the impeller centre and out along its blades. The centrifugal force hereby increases the fluid velocity and consequently also the kinetic energy is transformed to pressure.

The principles of the hydraulic components are common for most centrifugal pumps. The hydraulic components are the parts in contact with the fluid.

A leak flow will occur in the gap between the rotating impeller and stationary pump housing when the pump is operating. The rate of leak flow depends mainly on the design of the gap and the impeller pressure rise. The leak flow returns to the impeller eye through the gap. Thus, the impeller has to pump both the leak flow and the fluid through the pump from the inlet flange to the outlet flange. To minimise leak flow, an impeller seal is mounted.

The impeller seal comes in various designs and material combinations. The seal is typically turned directly in the pump housing or made as retrofitted rings. Impeller seals can also be made with floating seal rings. Furthermore, there are a range of sealings with rubber rings in particular well-suited for handling fluids with abrasive particles such as sand.

Achieving an optimal balance between leakage and friction is an essential goal when designing an impeller seal. A small gap limits the leak flow but increases the friction and risk of drag and noise. A small gap also increases requirements to machining precision and assembling resulting in higher production costs. To achieve optimal balance between leakage and friction, the pump type and size must be taken into consideration.

One approach to balance the axial forces is to make small holes in the hub plate. The leak flow through the holes influences the flow in the cavities above the impeller and thereby reduces the axial force but it results in leakage.

Another approach to reduce the axial thrust is to combine balancing holes with an impeller seal on the hub plate. This reduces the pressure in the cavity between the shaft and the impeller seal and a better balance can be achieved. The impeller seal causes extra friction but smaller leak flow through the balancing holes compared to the solution without the impeller seal.

References:

Cherkassky V. M. Pumps, fans, compressors: Textbook for heat and

power specialties of universities. 2-e Izd., pererab. I DOP. - Moscow:

Energoatomizdat, 1984. - 416 p.;

English - Russian terminology dictionary of heating, ventilation, air

conditioning and cooling. - Moscow: AVOK-PRESS, 2002. - 256 p;

Оnline resource grundfos;

Manual grundfos;

Оnline resource wikipedia..