Sizing and choice of pumps Part 1

1. Introduction

The pumps are essential elements in the industrial sector, they move the fluids

Whether they are hot or cold, clean or dirty. They carry out this operation in a

Extremely efficient and environmentally friendly.

In this chapter, we will calculate the various parameters needed, among others the

To select the appropriate pumps for our installation by referring to the

Supplier catalogs.

   II. General information about the pumps:

1. Definition:

Pumps are rotating machines that communicate to the fluid sufficient energy

In order to cause it to move in a piping network.

This part is detailed in Annex 3.

2. Choice of type of pumps:

In general, if the pressure of a fluid is to be increased,

Volumetric pumps, whereas if you want to increase the flow rate, you will rather use the pumps

Centrifugal.

The type of pumps suitable for our installation is centrifugal pumps, as

Data are: (See Figure 14)

Flow rate of 30 m3 / h

The pressure of 3.5 bar ..

3. The principle of operation:

The operation can be broken down into two steps: Suction: Liquid is sucked into the center of the rotor through an opening Distributor whose role is to conduct the fluid from the suction line to The inlet section of the rotor. The pump being primed, that is to say full of liquid, the Speed ​​of the fluid entering the wheel increases and hence the pressure in The hearing diminishes and thus generates suction and maintains the priming. Acceleration The rotor transforms the mechanical energy applied to the The machine in kinetic energy. At the outlet of the rotor, the fluid is projected into the The purpose of which is to collect the fluid and return it to the outlet section. The Section being given to the liquid being more and larger, its kinetic energy Transforms into pressure energy.

4. General characteristics of the pumps:

A) Flow

The flow rate qv supplied by a centrifugal pump is the volume displaced during the unit of time. It is expressed in cubic meters per second (m3 / s) or more in cubic meters Per hour (m 3 / h).

B) Gauge height:

The pump head H is the pump power supplied to the unit

Of the weight of the liquid passing through it.

C) Performance:

The efficiency of a pump is the ratio of the useful power P (hydraulic power)

Communicated to the liquid pumped to the absorbed power Pa.It is defined by:

With:
- qv: the volume flow of the fluid in m3 / h
- H: head
- Pa: Power absorbed by the fluid.
- e the density of the fluid.

D) Suction pressure limiting - NPSH - Cavitation

The "NPSH" "Net Positive Suction Head" is a characteristic given by the Manufacturer qualified as "NPSH required". In particular, it takes account of the The pressure which the fluid undergoes during its acceleration at the input of the wheel. For a pump to operate normally, the available (calculated) NPSH must be Greater than the required NPSH (as specified by the manufacturer). NPSH disponible > NPSH requis

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