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Pumping plants ( statii de pompare)

A pump is used to bring an amount of water from a given level. The pump evolved from thepiston pumps (with a low efficiency) to centrifugal pumps (with a high efficiency).

A pumping station is the whole assemble of pumps and pipes heightening he water level. The

figure presents a general scheme of a pumping station.

It can be seen that a pumping station has two distinctive parts:

1º absorption part; 2ºdispatching part ( partea de refulare)The absorption part creates an under pressure less than atmospheric pressure using the rotating

blades ( palete) and brings the water up into the pump. The dispatching pushes the water up from

the pump to the required level (usually into a tank).

The hydraulic performances of a pumping station are:Q p – the pumping flow (debit de pompare)

H m=ha+hr,a+href +hr,ref

H m is the manometric the height of actual (real) pumping height including the head losses(through hr,a and hr,ref )

m

p

i H Q A

P

102

'

where Pi – installed capacity (debit de pompare);

A’ – a coefficient depending on the nature of pumped liquid;

η – efficiency (randamentul)

The civil engineering is interested in the economical design of a pumping station refer to both,the investment and maintenance costs. Regarding the investment cost I it is made up of the pipe

cost ( I c) and pump cost ( I p). It the plane I-D ( D= the pipe diameter) the two costs I c and I p can be

graphically represented as follows:

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The upper curve I=I c+I p has a minimum, which correspond to the economical diameter Dec, using

the above expressions we get:

peciecm QP H ,,,,

Usually the values of these performance parameters cannot be ensured by one pump only. Several

pumps are needed, then the problem of linking then. There are several situations:

1. If a pump insures Q p /n (m2 /h) then we need n pumps that have to be linked in parallel

connections.

2. If a pump ensures H m /K meters, we need K pumps linked in series connection.

3. A combination of the two cases.

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WATER SUPPLY ( alimentare cu apa)

The problem of water supply involves two aspects that have to be taken care of, and fulfilled byevery water resource:

- the quantity of water

-

the quality of water

Water quality

We are referring to the properties of the drinking water. The properties of the drinking water maybe:

- physical properties

- chemical properties

- bacteriological properties

There are governmental (national and local) agencies that are responsible with the control of the

water quality and with issuing licenses for exploiting water recourses. This is not business of thecivil engineer.

Water quantity

When counting the necessary quantity of water several needs have to be considered:- domestic consumption (nevoi gospodaresti)

- industrial consumption (consum industial)

- public consumption (schools, hospitals etc.)

- streets (and other public places) cleaning- fire protection

- other needs

From the civil engineer point of view, these needs take the form of necessary flow (debit

necesar )for the entire town and which is divided per capita. The necessary flow can also be

expressed in several forms called specific flows:- annual flow Qan;

- daily average flow Q zi,med =Qan /365. It is used rather as an indicator to compare the water

consumption in several places;- daily maximum flow Q zi,max=K ziQ zi,med . This flow is used as a computation flow Qc for the

entire water supplying system except supplying networks (for collecting wells, tanks,

pump stations, etc.). The relation Q zi, max versus Q zi,med can be seen in the figure:

hourly average flow (debit orar mediu)

Qorar,mediu=Q zi,max / 24

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hourly maximum flow (debit orar maxim)

Qorar,max=K 0Qorar,mediu

The variation of Qorar is a mirror of the activity in that area: a bigger variation reflects a lack of acontinuous industrial activity, while smaller differences reflect a rich industrial activity. The two

different situations described above can be also expressed in terms of K 0:K 0>1,2 and respectively

K 0<1,2.

Water supply system (wss)A wws is made of all construction works and installations aiming at binging the water from its

places to the user.

The figure below shows a wws.

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Where: 1. water intake (water catching) (captarea de apa)

2. pump station of the first step (statie de pompare de treapta I )

3. water treatment station (statie de tratare a apei)4. water tank

5. pump station of the second step

6. balancing reservoir (reservoir de compensare)

7. water supply network 8. aqueduct (aductiune).

Depending on a local conditions, some of the above mentioned components may not be

necessary: fo instance 2 and 4 if a gravitational flow is possible by the natural relief; 3 if thequality of water is very good, etc.

We have studied so far the components 2, 5 and 7. We go now further and study the water

catching, water treatment station and water tanks.

1. Water catching

The water catching may be achieved from aquifer layers (using wheels or drains, see last lecture),

from water streams (rivers etc.) and from natural or artificial lakes. From the civil engineer pointof view the water catching does not bring special problems.

2. Water treatment station

In figure below, a water treatment station scheme is given:

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Where: 1. sand cleaning basin (deznisipator )

2. water coagulation station (statie de coagulare a apei)

3. settling tank (decantor )4. filter plant (state de filtrare)

5. decontamination plant (statie de dezinfectie)

All these components have the objective of reducing certain quantities of substances and particles

contained the water.

3.1. Sand cleaning basin

It retains particles down to 0,2 cm in diameter. Usually a sand cleaning basin retains about 25%-30% of all solid particles. The water cleaning is based on the water settling velocity ( viteza de

decantare a apei).

The size (length) of the basin is given by the magnitude of the resultant velocity R.

vs is the settling velocity of the solid particles

vs is the water velocity in the basin.

There are two types of the sand clearing basins:- horizontal basins

- vertical basins

(see the figure bellow)

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The type of the basin depends on the area that is at the disposal of the designer: a vertical basin

needs a smaller area. In the case of vertical basins the sand settling requires that va<vs.

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