Water lifting devices (2022)

3.1 PRINCIPLES FOR LIFTING AND MOVING WATER

Water may be moved by the application of any one (or any combination) of six differentmechanical principles, which are largely independent, i.e. by:

  1. direct lift
    this involves physically lifting water in a container
  2. displacement
    this involvesutilizing the fact that water is (effectively)incompressible and can therefore be "pushed" or displaced
  3. creating a velocity head
    when water ispropelled to a high speed, the momentum can be used either to create a flow orto create a pressure
  4. using the buoyancy of a gas
    air (or othergas) bubbled through water will lift a proportion of the water
  5. gravity
    water flows downwardunder the influence of gravity

3.2 TAXONOMY OF WATER LIFTS AND PUMPS

Familiesof pumps and lifting/propelling devices may be classified according to which ofthe above principles they depend on. Table 5 is an attempt to classify pumps under the categories given above. It willbe seen that most categoriessub-divide into the further classifications "reciprocating/cyclic"and "rotary". The first of these relates to devices that are cycled through a water-liftingoperation (for example a bucket on a rope is lowered into the water, dipped to make it fill, lifted, emptied and then the cycle is repeated); in suchcases the water output is usually intermittent, or at best pulsating rather than continuous. Rotary devices weregenerally developed to allow agreater throughput of water, and they also are easier to couple to engines or other types of mechanical drive. Therefore, bydefinition, a rotary pump willgenerally operate without any reversal or cessation of flow, although in some cases the output mayappear in spurts or pulsations.

Before considering the differences between thediverse options available for liftingwater, it is worth briefly noting the factors they all have in common. Virtually all water liftingdevices can best be characterized for practical purposes by measuring their output at different heads and speeds. Normally the performance of a pump ispresented on a graph of head versus flow (an H-Q graph, as in Fig. 16) and in most cases curves can be defined for the relationship between H and Q atdifferent speeds of operation. Invariably there is a certain head, flow and speed of operation that represents theoptimum efficiency of the device,i.e. where the output is maximized in relation to the power input. Some devices andpumps are more sensitive to variations in these factors than others; i.e. someonly function well close to a certain design condition of speed, flow and head,while others can tolerate a wide range of operating conditions with little lossof efficiency. For example, the centrifugalpump characteristic given in Fig. 16 shows an optimum efficiency exceeding 80%is only possible for speeds of about 2000 rpm.

Water lifting devices (4)

Fig. 16Typical curves showing relationship between head, flow, speed and efficiency (example given for acentrifugal pump)

The rest of this Section describes in somedetail each of the devices given in the Taxonomy of Pumps andWater Lifting Devices of Table 5.

3.3 RECIPROCATING AND CYCLIC DIRECT LIFTDEVICES

3.3.1 Watering cans, Buckets, Scoops, Bailersand the Swing-Basket

These areall variations on the theme of the bucket, are hand-held and must be theearliest artificial methods for lifting and carrying water. The watering can iseffectively a bucket with a built-in sprinkler and represents an efficient, butlabour intensive method for irrigating very small land-holdings. Artisan-madewatering cans are quite widely used in Thailand. Scoops, bailers (Fig. 17) andthe swing-basket (Fig. 18) represent methods of speeding up the process of filling, lifting andemptying a bucket; the latter also uses two people rather than one and thereby increases the mass of water that can bescooped in each swing. These are more fully described in Section 4.2 in the context of using human musclepower, since they have evolved in such a way as to fit the human prime-moverbut to be unsuitable for any kind of mechanization. They are rather inefficientas water is lifted over lm and allowed to fall back to 0.3-0.5m, which is theapproximate operating head for devices of this kind.

Table 5 TAXONOMY OF PUMPS AND WATER LIFTS

√ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ **** √ – – – – –

Category and Name

Construction

Head
range
(M)

Power
range
(W)

Output

Efficiency

Cost

Suction Lift?

Status
for
Irrigation

IDIRECT LIFT DEVICES

Reciprocating .'cyclic

Watering car.

1

>3

*

*

*

*

x

Scoops and bailers

1

>1

*

**

*

*

x

Swing basket

1

>1

*

**

*

*

x

Pivoting gutters and "dhones"

2

1-1.5

*

**

**

**

x

Counterpoise '.lit or "Shadoof"

2

1-4

*

**

**

**

x

Rope & bucket and windlass

1

5-50

*

*

*

*

x

Self-emptying bucket or "mohte"

2

3-8

**

***

*

**

x

Reciprocating bucket hoist

3

100-500

****

****

***

****

x

x

Rotary/continuous

Continuous bucket pump:

2

5-50

* *

**

***

**

x

Persian when', or "tablia"

2

3-10

**

***

***

**

x

Improved Persian wheel "zawaffa"

2

3.15

***

****

****

***

x

Scoop wheels or "sakia"

2

>2

**

****

****

****

x

Waterwheels or "noria"

2

>5

*

**

**

**

x

IIDISPLACEMENT PUMP

Reciprocating/cyclic

Piston/bucket pumps

2& 3

2-200

***

***

*****

****

Plunger pumps

3

100-500

***

**

****

*****

?

Diaphragm pumps

3

5-10

**

***

****

***

"Petropump"

3

10-100

**

**

*****

****

?

Semi-rotary pumps

3

5-10

*

**

**

**

x

Gas or vapour displacement

3

5-50

****

****

***

***

√ or x

?

Rotary/continuous

Gear and lobe pumps

3

10-20

*

*

**

***

X

Flexible vane pumps

3

10-20

**

***

***

****

X

Progressive cavity (Mono)

3

10-100

***

***

****

****

x

?

Archimedean screw

3

>2m

**

****

***

***

x

Open screw pumps

3

>6m

****

*****

****

*****

x

Coil and spiral pumps

2

>6m

**

**

***

***

x

Flash-wheels & treadmills

2& 3

>2 m

**

****

**

**

x

Water-ladders "Dragon spines"

2

>2m

**

***

***

***

x

Chain (or rope) and washer

2 & 3

3-20m

***

***

****

****

x

Peristaltic pump

3

>3m

*

*

***

***

x

Porous rope

3

3-10m

**

**

?

?

x

?

III VELOCITY PUMPS

Reciprocating/cyclic

Inertia and "joggle" pumps 2& 3

2-4

*

**

****

**

x

Flap valve pump 1 & 2

2-4

*

*

**

*

x

Resonating joggle pump 2

2-10

**

****

****

***

x

?

Rebound inertia 3

2-60

**

*

****

***

x

Rotary/continuous

Propeller (axial flow) pumps

3

5-3

****

*****

****

****

x

Mixed flow pumps

3

2-10

****

*****

****

****

x

Centrifugal (volute) pumps

3

3-20+

*****

*****

****

***

Centrifugal (turbine) pumps

3

3-20+

*****

*****

****

****

Centrifugal (regenerative) pump;

3

10-30

***

***

***

x

Jet pumps (water, air or stream)

3

2-20

***

**

**

***

x

x

IVBUOYANCY PUMPS

Air lift 3

5-50

**

***

**

****

x

x

VIMPULSE PUMPS

Hydraulic ram

3

10-100

**

**

***

***

x

VIGRAVITY DEVICES

Syphons

1, 2 & 3

1.(1-10)

*****

**

Qanats or foggara

2

–

–

**

*****

Construction: 1 Basic 2 Traditional 3 Industrial

Very low

***

Medium-high

*****

Yes√

Yes√

Low-medium

***

High

*****

No x

Possible ?

Medium

***

Unlikely x

Water lifting devices (5)

Fig. 17 The scoop used as a simple handtool

Water lifting devices (6)

Fig. 18 The swingbasket in use (after T.Schioler [24])

Water lifting devices (7)

Fig. 19 Scoop with a rope support

3.3.2 SuspendedScoop, Gutters, Phones (or Doons) and theCounterpoise-lift or Shadoof

Thenext: stage of technical advance is to support the mass of water being liftedby mounting the scoop or bucket on a suspended pivoted lever to produce aswinging scoop (Fig. 19) or a see-sawing gutter or "dhone" (Fig. 20)which also operate through low lifts (0.5-lir.) at relatively high speed. Thewater container can be balanced with a weight; Fig. 21 shows a counterpoiselift, alias water-crane or "shadoof".

If theterrain permits, such as on a sloping river bank, several "shadoofs"can be used to lift water in stages through a greater height than is possiblewith one.

Water lifting devices (8)

Fig. 20 Dhone as used in Bangladesh

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Fig. 21 Counterpoise lift

3.3.3 Bucket hoists, Windlasses, Mohtes andWater Skips

To increasethe lift it becomes necessary to introduce a rope to pull the container ofwater from the source to a level where it can be tipped into the conveyancechannel. There is therefore a family of devices for pulling up a container ofwater on a rope. The simplest form for this is a rope and bucket, which in animproved form has a simple windlass, i.e. a hand operated winch, to increasethe leverage and hence the size of bucket that can be lifted.

The output of such systems is generally toosnail for irrigation, (they tend to be used mainly for domestic or livestockwater supply duties), but by powering the device with animals, usually oxen,sufficient water can be lifted to irrigate even through heads of 5-10m. Thisencouraged the evolution of the "self-emptying bucket", known inIndia as a "mohte", (Figs. 22 and 92). These commonly have a bucketmade of leather or rubber, with a hole in its bottom which is held closed by aflap which is pulled tight by a second rope harnessed to the animals. Thenumber in use today is still in the order of a million or more, so this deviceremains of considerable importance in some regions. Mohtes are discussed inmore detail under Section 4.3 dealing with animal power as a prime mover.

Water lifting devices (10)

Fig. 22 Self-emptying mohte with inclined tow path

3.4 ROTARY DIRECT LIFT DEVICES

Itgenerally improves both efficiency and hence productivity if the water liftingelement can move on a steady circular path rather than being cycled orreciprocated. The reason for this is that the energy input to any water liftingdevice is usually continuous, so that if the output is intermittent, unlessenergy can be stored during the parts of the cycle when no water is lifted, itis lost. Therefore reciprocating/cyclic devices tend to be less efficient thanrotary devices; this is not a firm rule however, as some reciprocating devicesinclude means to store energy through the non-productive part of the cyclewhile some rotary devices are less efficient for other reasons.

3.4.1 Bucket elevators, Persian wheels andNorias

An. obvious improvement to the simple rope andbucket is to fit numerous small buckets around the periphery of an endless beltto form a continuous bucket elevator. The original version of this, which isancient in origin but still widely used, was known as a "Persianwheel" (Figs. 23, 94 and 95); the earliest forms consisted of earthenwarepots roped in a chain which is hung over a drive wheel. The water powered"noria" (Figs. 24, 151 and 152), a water wheel with pots, buckets orhollow bamboo containers set around its rim, is similar in principle except thecontainers are physically attached to the drive wheel circumference rather thanto an endless belt suspended from it.

Theflow with any of these devices is a function of the volume of each bucket andthe speed at which the buckets pass across the top of the wheel and tip theircontents into a trough set inside the wheel to catch the output from thebuckets. Therefore, for a given power source and speed of operation roughly thesame number of containers are needed regardless of head. In other words, ahigher head Persian wheel requires the buckets to be proportionately morespaced out; double the head and you more or less need to double the spacing.

ThePersian wheel has been, and still is, widely used particularly in the north ofthe Indian sub-continent and is discussed in more detail under Section 4.3 onAnimal Power, while the noria was widely used in China, S.E. Asia and to someextent in the Middle East and being normally water powered is discussed in moredetail in Section 4.9. Both devices are tending to be replaced by more modernmechanical water lifting techniques as they are old-fashioned and low inoutput. It should be noted that the term "Persian wheel" is sometimesused to describe other types of animal powered rotary pumps.

Although Persian wheels and norias aremechanically quite efficient, the mainsource of loss from these types of device is that somewater is spilled from the buckets and also there is a certainamount of friction drag caused when thebuckets scoop up water, which again reduces efficiency. Also, the Persian wheelis obliged to lift the water at least 1 m (or more) higher than necessarybefore discharging it into a trough, which can significantly increase thepumping head, particularly in the case of low lifts. The traditional woodenPersian wheels also inevitably need to be quite large in diameter toaccommodate a large enough collection trough to catch most of the waterspilling from the pots; this in turn requires a large well diameter whichincreases the cost.

Water lifting devices (11)

Fig. 23 Persian wheel

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Fig. 24 Noria

Some performance figures for animal poweredPersian wheels are given in Molenaar; [1].

Height lifted

Discharge

9m

8-10m3/h

6m

10-12m3/h

3m

15-17m3/h

1.5m

20-22m3/h

Dependingon the assumption used for the power of the animals in the above examples, theimplication is that the efficiency is in the order of 50% at medium lifts suchas 6m and perhaps marginally better at higher lifts but worse at lower lifts.

The water-powered noria uses the sameprinciple as the Persian wheel and therefore also needs to be of largerdiameter than the pumping head, which either limits it to very low lift pumpingor requires very large, cumbersome and expensive construction. Small, low-liftnorias, used in Thailand and China, are very inexpensive while much largernorias are used in Vietnam and Syria. Some of the largest in Syria exceed 10min diameter, but in relation to their size they tend to be unproductivecompared with more modern pumping systems. A fuller description of Vietnameseand other norias is given in Section 4.9

3.4.2 ImprovedPersian wheel, (Zawaffa or Jhallar)

Traditionalwooden Persian wheels were fitted with earthenware water containers, but avariety of all-metal improved Persian wheels have been built, some ascommercial products, in China, India, Pakistan and Egypt. Metal Persian wheelscan be made smaller in diameter, which reduces the extra height the water needsto be lifted before it is tipped out of the containers, and also reduces thewell diameter that is necessary.

A modifiedversion of the Persian wheel used in Syria and also in Egypt (where it iscalled the zawaffa or jhallar) includes internal buckets within the drive wheelwhich catch the water and direct it through holes in the side plate near thehub into a collection trough; Fig. 25. This reduces both splashing and spillagelosses and the extra height above the collection channel at which the water istipped. Roberts & Singh [13] gave figures for a modernised metal Persianwheel, of 153m3/h lifted through 0.75m. This implies that efficiencies as highas 75% are possible with modernised devices, which are rather good.

3.4.3 Scoop-wheels;Sakia, Tympanum or Tablia

The scoop-wheel (sakia in Egypt where itoriginated) has some factors in common with the noria. Although widely used inEgypt it has failed to become popular anywhere else. It is however an efficientand effective device; Fig. 26.

Water lifting devices (13)

Fig. 25 Zawaffa type Persian wheel
(side wall shown partially removed)

Water lifting devices (14)

Fig. 26 Sakia or Tympanum (electrically powered in this case)

Itconsists of a large hollow wheel with scoops around its periphery, whichdischarges water at or near its hub rather than from its top. The diameters forsakias range from about 2-5m; since water discharges at their hub level, therule of thumb used in Egypt is that a sakia will lift water through a head ofhalf its diameter less 0.7 m, to allow for the depth of submergence of the rimin order to scoop up water effectively. Therefore sakias of diameters from 2-5mwill lift water from 0.3-1.8m respectively.

Sakiasare now normally made from galvanized sheet steel. Second-hand vehicle rollerbearings are commonly used to support the substantial weight of a sakia and itswater contents. Most sakias are animal powered, but they are increasingly beingdriven by either mains electric motors or small engines, via suitable reductiongearing. The normal operating speed is 2-4 rpm for animal-driven sakias, and8-15 rpm for motorised or engine-powered units.

Variousdifferent spiral shapes have evolved for the internal baffle plates in thesakia, and the Hydraulic Research and Experimental Station (HRES) in Egypttested various models to try to determine the optimum design. The best shapeddesigns, such as in Fig. 27, were measured as being as much as 50% better thanthe worst. Since some 300 000 sakias are in use in the Nile valley and Delta,optimization of the design could yield substantial aggregated benefits. Animportant feature of the the three most successful sakia variants tested isthat the outer compartments divided bythe internal baffleplates discharge first into individual collectionchambers which in turn discharge through holes surrounding the hub instead ofhaving a common discharge orifice as on the more traditional designs. This prevents waterrunning back into the compartment adjacent to it.

Water lifting devices (15)

Fig. 27 The Fathi is the optimum design of Sakia

The types ofsakia with separate discharge points for each compartment are distinguished by the generic name"tablia". A further advantage of the tablia type of device is thatthe water discharges a few centimeters above the centre shaft and thereforeincreases the useful head in relation to the diameter; especially with smallermachines. Typically a 3m tablia will lift water 1.5m compared with 0.90m for acentre-discharge sakia.

Another important conclusionfrom the tests by HRES was that for wheelsoperated in the 2-15rpm range, 6-8 compartments provide the optimumdischarge. According to Molenaar [1], the following performance might beexpected from traditional sakia designs:

diameter of
sakia

head
lifted

output
5m

1.8m

36m3/h

4m

1.3m

51m3/h

3m

0.9m

75m3/h

2m

0.3m

114m3/h

Comparison ofthe above outputs with those from a traditional persian wheel indicate that the sakia is somewhatmore efficient, although of course it cannot lift water as high as is possiblewith a persian wheel.

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