Water Pump Systems and Energy Saving

The difference between centrifugal pumps and positive displacement pumps:

Centrifugal pumps are a kind of pumps to add energy continuously; volumetric pumps are pumps that periodically add energy to a certain amount of water. The market share of centrifugal pumps is about 70%.

Flow: The amount of fluid conveyed by the pump in a unit of time is called flow. Flow rate with the symbol Q, the unit commonly used m3 / h, m3 / min and m3 / s.

Lift: the pump conveys a unit weight of fluid from the inlet to the outlet of the energy head value-added known as the head. Lift with the symbol H, its unit is m, customarily known as meters of liquid column height.

Rotation speed: The number of revolutions per minute of the pump rotor is called the rotation speed, indicated by n, the unit is r/min.

Power:

Input power: also known as shaft power, is the prime mover transferred to the pump shaft power, expressed in P, the unit is kW.

Output power: also known as effective power or water power, is the power obtained from the fluid being pumped.

Efficiency:

The input power of the pump can not all be transferred to the fluid being conveyed, which must be part of the energy loss. The actual power of the fluid being conveyed and the ratio of the input power of the pump is called the efficiency of the pump, expressed as the symbol η.

Cavitation margin: pump cavitation margin refers to the unit weight of the liquid from the pump suction mouth to the impeller inlet pressure of the lowest inlet pressure reduction, known as the net positive suction head (NPSH).

NPSHA: Effective margin of vaporization (NPSHA): Effective margin of vaporization (NPSHA) refers to the pump suction inlet of a unit weight of liquid with more than saturated vapour pressure of the rich energy, it is a function of the system and flow.

Necessary vapor corrosion margin (NPSHR): necessary vapor corrosion margin (NPSHR) is a unit weight of liquid from the pump suction inlet flow to the impeller blade inlet pressure at the lowest pressure drop, it is a function of the pump and flow.

Effective cavitation allowance (NPSHA) is greater than the necessary cavitation allowance (NPSHR), the pump will not appear cavitation phenomenon.

Volumetric pump applications: high pressure / low flow application conditions; highly viscous fluid media application conditions; precise control of flow application conditions.

Centrifugal pump classification: vane shape (runoff, mixed, axial); vane sidewalls (fully open, half-open, closed); suction type (single or double suction); number of stages (single-pole or multi-pole); collector (volute or diffuser shape); orientation (vertical or horizontal).

Piping configuration optimization principle:

A uniform flow field distribution is established upstream of the pump, and a straight pipe section should be taken at the inlet of the pump.

It is recommended that the inlet flow rate does not exceed 1.5m/s, minimizing the loss of pressure head on the inlet side of the pump to reduce the risk of cavitation.