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The present use of pumps in aquaculture are:

  1. As a total or supplementary means of obtaining water for the purpose of maximizing production per unit area or volume, say in ponds or tanks.

  2. As aerators, water circulation device or for effecting continuous flow system in intensive culture where water quality deteriorates rapidly and becomes a limiting factor.

  3. For lifting water in sites where the elevation is beyond the ample reach of tidal fluctuation; where the source is ground-water, whether saline or fresh; or where the cost of excavation is more expensive than the cost of pump and its operation.

8.1 Terminology used in pumps

A number of technical terms can be helpful in understanding the selection, installation and operation of pumps for coastal aquaculture.

  1. Suction head. Refers to the vertical distance from the surface of water (including drawdown, if any) to centreline of the pump impeller.

  2. Discharge head. Is the vertical distance from the centreline of the impeller to point of discharge.

  3. Total Dynamic Head (TDH). Is the sum of the suction head, discharge head, hydraulic head losses and the velocity head.

  4. Drawdown. Is the lowering of water surface below the static level during pumping.

  5. Static level. Is the water level before pumping begins.

  6. Hydraulic loss. Is loss due to pipe wall friction, elbow design, joints, gate valves, sudden reduction or enlargement of pipe size. This is expressed in its equivalent height or head of water loss.

  7. Discharge or capacity. Refers to the rate of flow or the volume of water pumped per unit time such as gallons per minute; cubic feet per second; cubic meters per minute; liters per second; etc.

  8. Performance curves. Is the variation of head with capacity at a constant impeller speed. It also includes efficiency and brake horsepower curves.

8.2 Types of pumps for aquaculture

Coastal aquaculture operations may require both freshwater and brackishwater. Freshwater may be needed for maintaining salinity of water during dry months due to rapid evaporation or for staff use or for domestic animals in an integrated farming set-up. Hence, pumps suitable for freshwater and brackishwater are discussed.

Pumps may be differentiated in how the water is forced from the intake to the discharged side, as well as the height of water lift and corresponding discharge. Under this differentiation, there are three main types, namely: (i) centrifugal: (ii) deep-well turbine; and (iii) propeller.

8.2.1 Centrifugal pump

This pump is characterized by operating at low head and low discharge. For best performance, the pump should be set close to the water level with a total suction lift usually not more than 6 m.

The pumps operates on the principle of centrifugal action. A motor or driver rotates an impeller with vanes immersed in water and enclosed in a casing. Water that enters the case is immediately engaged in by the rapidly rotating impeller. This rotation causes a flow from the centre of the impeller to the rim or outside of the case where pressure head is rapidly built up. To relieve the pressure, the water escapes through the discharge pipe. The centrifugal pump will only operate if the case is entirely full of water or primed and air-tight. The kinds under this category are the volute centrifugal pumps which include self-priming models (Fig. 8.1 and 8.2).

8.2.2 Deep-well turbine pump

This is capable of operating at high head and low to high discharge. It is used in cased wells or situations where the water lift is below the practical limits of a centrifugal pump. Successful installations have been made for lifts up to 300 m and capacities up to 7 000 gpm or 441 liters per sec. Deep-well turbines are much more expensive than centrifugal pumps and are more difficult to inspect and repair.

Fig. 8.1

Fig. 8.1 Horizontal centrifugal pump cross section

Fig. 8.2

Fig. 8.2 Self-priming volute pumps

The turbine has three main parts: (i) head; (ii) pump bowl; and (iii) discharge column (Fig. 8.3). The pump bowl is always placed beneath the water surface of the well. Fluctuation in the water table is determined prior to installing the pump so that the bowls of the turbine can be placed below the farthest drawdown point (Fig. 8.4.). The depth at which the bowls are located is called depth of setting. Since well diameters are relatively small, it is often necessary to use more than one impeller or one-stage pump. The head or height of lift produced by a multi-stage pump is proportional to the number of stages or bowls.

Fig. 8.3

Fig. 8.3 Deep-well turbine pump

Fig. 8.4

Fig. 8.4 Turbine pump installation

8.2.3 Propeller pump

This pump has the characteristic of operating at low head but delivering large volume of flow. In almost all brackishwater aquaculture farms, ponds are constructed close to the water or within the tidal range. This makes the total dynamic head (TDH) to be as low as possible within the range of pumps designed for low head and large discharge.

Single-stage propeller pumps are limited to pumping against heads of around 3 m. By adding additional stages or bowls, 9 to 12 m heads are obtainable.

There are three basic designs of propeller pumps namely: (i) radial-flow; (ii) mixed-flow; and (iii) axial flow. All these three pumps have shaft to which impeller bowls are attached and submerged with the pump operating at proper submergence depth. A brief characteristic of the three pumps are given in Table 8.1.

Table 8.1
Characteristics of different types of propeller pumps

Propeller pumpDifferentiating characteristics
Radial flow
(Fig. 8.5)
1.Water enters the pump and thrown at 90° angle towards the wall of the bell.
2.Energy or force imparted to the liquid is all centrifugal.
3.Delivers flow at higher heads than the other two but less volume for the same power.
4.Normally operates at speeds up to 3 600 rpm, generally higher than the two.
(Fig. 8.6)
1.Water entering the pump is thrown to the bell wall at an angle of 40° to 80° of the shaft.
2.Force imparted is combination of centrifugal and displacement energy.
3.Available at capacities over 30 000 gpm.
4.Normally operates at speed of 1 760 rpm. The usual speed of electric motor; hence, suitable to install where electricity is available.
(Fig. 8.7)
1.Water enters the pump parallel to the shaft and is lifted also parallel with the shaft; hence, all force imparted is displacement energy.
2.Hydraulic head range is up to 6 m per stage.
3.Available at capacities up to 500 000 gpm.
4.Operates at speed of about 1 160 rpm and higher.
Fig. 8.5

Fig. 8.5 Radial flow propeller pumps

Fig. 8.6

Fig. 8.6 Mixed flow propeller pumps

Fig. 8.7

Fig. 8.7 Axial flow propeller pumps

Among the three propeller pumps, the axial-flow with TDH of up to 7.5 m per stage falls within the usual range of operation necessary in brackishwater fishponds. One stage is only needed as the head required seldom exceeds 3 m TDH, because tidal fluctuation are slightly greater than 2 m only.

8.2.4 Special types of pumps

There are two main types of special pumps developed in Thailand—the so-called dragon-wheel pump and the push pump. Both pumps are being used in shrimp ponds and suitable for low lifts of water such as from tidal water.

(a) Dragon-wheel pump. This is a simple type of pump which delivers water into the pond by using a wooden trough. Inside the trough is a series of blades connected by flexible joints and being moved by an axle which is being turned by a wheel. The wheel is connected by belt to the driving engine or windmill. The lower end of the pump is always submerged in water. As the series of blades moves along the trough, water is trapped and lifed to the pond (Fig. 8.8). The specifications of existing wheel pumps as given by Tharnbuppa (1982), are as follows:

Fig. 8.8

Fig. 8.8 Dragon wheel pump run by engine and windmill (After Tamiyavanich, 1977)

 Parts of pumpDimension/size
1.Engine (diesel, low rpm)3.5; 8–10 hp
2.Wheel diameter114–127 cm
3.Length of axle3 m
4.Wooden trough:length5–6 m
width17.8–30 cm
5.Blade width15.2–27.9 cm

(b) Push pump. This type is suitable for lifting water at an inclination of not more than 20°. This type has been used in Thailand within the last 10 years and some data on existing installation and area capacity are shown in Table 8.2. The water is being pushed up by means of a propeller through a tube or pipe such as asbestos, to a water conveyor in large volume. The propellers are made to rotate at a third or fourth of the engine rpm (300 to 500 rpm) (Jamandre, 1977). It was estimated that the rate of flow using a 120-Hp engine is about 5 196 m3 per hour (Tharnbuppa, 1982).

The pump unit consists of five main parts and accessories as follows: (i) diesel engine; (ii) propeller shaft with length of 6 to 8 m; (iii) propeller, 2–3 blades; (iv) pipe, concrete or asbestos; and (v) propeller shaft joints (Fig. 8.9).

Table 8.2
Some data on push pump installation in Thailand (after Tharnbuppa, 1982)

Size of engine (hp)Fuel consumption (1/hr)Diameter of shaft casing in. (cm)Shaft diameter in. (cm)Propeller diameter in. (cm)Pipe column diameter in. (cm)Area capacity (ha)
40–7562–3 (5–8)1 (2.5)12 (30.5)16 (40.6)4
120–15010–123 (7.6)1.5 (3.8)16 (40.6)20 (50.8)8
180 to 220
or more
10–123 (7.6)2 (5)20 (50.8)24 (60.9)16
Fig. 8.9

Fig. 8.9 Push pump and installation (After Tharnbuppa, 1982)

The sizes of engine for push pumps are somewhat oversized because they are reconditioned automotive diesel engines of trucks that are repaired and bought cheap. Where electricity is available, electric motors are used instead of diesel engine. At least 20 Hp motor should be used for the pump.

Where the engine is over-sized for the driven push pump, the extra power may be used for another purpose such as pumping underground water for mixing with seawater to reduce pond water salinity and for household use.

An exmple set-up is to add a unit of air compressor in the engine-push pump assembly. In this set-up, the engine will operate the air-compressor while also operating the push pump. From the compressor the high-pressured air is introduced into the pipe casing of a well above the water surface. The air pressure will then push the water into another pipe in the casing which is the water supply type (Fig. 8.10). This follows the principle of operation of an airlift pump.

Push pump is also to gather shrimp fry from the tidal canal for the pond aside from being a supplementary water source for the pond system. The shrimp seeds are drawn through the pump column and mortalities are estimated to be less than 20 percent due to the low impeller rpm. The gathered fry are then treated with saponin which selectively kills finfish species but not the shrimp fry. The fry are then allowed to enter the pond for culturing.

8.3 Selection of pump

The above discussion on pump provides a general basis in the selection of the type of unit. The final selection of pump is enhanced if one has knowledge of the characteristic performance curves of a particular pump which is usually available from the manufacturer. Examples of pump performance curves for the turbine propeller pumps are shown in Figs. 8.11 and 8.12.

Fig. 8.10

Fig. 8.10 Combination pump (After Tharnbuppa, 1982)

The characteristic performance curves provide a guide in the proper operation of a pump and indicate what could be expected of it or what it can do for different capacities at various speeds. The curve has two-fold purposes: (i) selection of a pump that will give maximum efficiency under any local condition; and (ii) adapt the pump to the best operating condition at the lowest possible cost or best efficiency.

For the pump installation in Fig. 8.4 and pump characteristic performance curves in Fig. 8.12, a verification whether given data are accurate may be made as follows:

Fig. 8.11

Fig. 8.11 Performance curves for propeller pumps (After Jamandre, 1982)

Fig. 8.12

Fig. 8.12 Pump characteristic performance curves for deepwell turbine pump

  1. The discharge Q = 1 200 gpm.

  2. The total dynamic head (TDH) as determined from the pump installation can be verified from the data below.

    a)Suction head55(16.77)
    b)Discharge head25(7.62)
    c)Friction head in discharge and suction pipeline, 375 (320 + 55) of 8" pipe at 1 200 gpm = 375 x 2.2/100 ft/ft-(from Table 8.3) 8.25 + (2.51)8.25(2.51)
    d)Friction head in fittings — equivalent length of two 45° angle fitting, 8" diameter (Table 8.4) is 10 × 2 = 20 ft; loss is 20 x 2.2/100 ft/ft0.44(0.13)
    e)Velocity head at end of discharge, 8" diameter and 1 200 gpm, velocity is about 7 ft/sec;
     0.76 (0.23)

An analysis of the pump characteristic curves (Fig. 8.12) shows the following: At Q = 1 200 gpm, head capacity = 90 ft (27.4 m) and brake horsepower = 33, the efficiency is 82 percent.

The comparison shows that at the given requirements of the installation, the pump has the necessary head capacity and is about at peak efficiency.

8.4 Components of a pumping plant

The components of a pumping plant in coastal fish farm are as follows:

  1. Pump and prime mover foundation. The bearing capacity of the concrete foundation must be sufficient to carry the weight of the pump and engine or motor driver. Considerations in the layout and elevation of pump and the prime mover must be given to the: (i) suction lift limitation; (ii) highest flood level; and (iii) accessibility and economy.

  2. Suction sump. A sump is a basin provided at the foot of the pump column suction end. This protects the system against excessive debris, floatsam and also minimizes silting.

  3. Distribution canals. These consist of main and secondary canals of the fishponds including a stilling basin or pool to which the pump directly discharges.

8.5 Design of suction sump

The design of suction sump should consider: (i) strainers and trash rack; (ii) spacing between a number of pump units; (iii) sump intake or flow pattern; (iv) submergence; and (v) clearance from floor and walls. Correct and incorrect location and spacing of suction ends are illustrated in Figures 8.13 and 8.14.

Proper depth of submergence of suction bell is to be observed in order to avoid cavitation and vortices in suction sump. The lower edge of the suction bell must have a depth of submergence of at least 1.5 m for usual velocity of water in pipes of about 8 ft per sec (2.4 m/sec.). For other velocities, Figure 8.15 may be used. The minimum allowable should be equal to the diameter of the suction bell. The suction bell, on the other hand, should not be less than twice the impeller hub in order to keep the pump self-priming during operation time (Jamandre, 1977). When vortices appear, baffles may be provided in the sump to avoid it. Figure 8.16 provides some idea on the location or design of baffles for some arrangement of suction pipe.

Adequate floor and wall clearances between the suction bell and the sump should be provided. This clearance should be equal to the diameter of the bell itself. Figure 8.17 illustrates the flow pattern or distribution at the entrance of a suction bell in relation to its distance from the suction floor and wall.

Table 8.3
Friction loss of water, in feet per 100 ft of clean wrought-iron or steel pipe*

Flow, gpmNominal diameter of pipe, in.
40 23.510.793.101.280.440.12     
75  35.810.14.131.390.280.12    
120   24.710.03.370.880.200.12   
170   48.419.66.531.670.540.22   
200   66.326.78.902.270.740.300.08  
260    44.514.  
280    51.316.94.301.380.560.14  
300     19.24.891.580.640.16  
400     33.98.472.721.090.280.09 
500     52.513.04.161.660.420.140.06
600      18.65.882.340.600.190.08
700      25.07.933.130.800.260.11
800      32.410.
900      40.812.
1 000
1 100       19.07.411.870.590.25
1 200       22.58.762.200.700.30
1 300        10.22.560.820.34
1 400        11.82.950.940.40
1 500        13.53.371.070.45
2 000        23.85.861.840.78
3 000
4 000         22.66.992.92
5 000          10.804.47

* Reprinted from “Tentative Standards of Hydraulic Institute, Pipe Friction,” Copyright 1948 by the Hydraulic Institute, 122 E. 42d St.,New York, New York, 10017.

Fig. 8.13

Fig. 8.13 Correct and incorrect sump designs for minimum entrained air into suction line
(After Jamandre, 1982)

Table 8.4
Length of steel pipe, in feet, equivalent to fittings and valves*

Nominal size, in
90° elbow2.
45° elbow1.
Too, side outlet5.
Close return band6.
Gate valve0.
Globe valve27.
Check valve10.513.215.821.126.431.742.352.863.081.0105.0125.0
Foot valve24.

* Courtesy the Gormon-Hupp Company

Fig. 8.14

Fig. 8.14 Section sump design showing proper spacing
(After Jamandre, 1977)

Fig. 8.15

Fig. 8.15 Minimum suction pipe submergence for various pipe flow velocity
(Source: Goulds pumps manual)

Fig. 8.16

Fig. 8.16 Baffle arrangement for vortex prevention
(After Jamandre, 1977)

Fig. 8.17

Fig. 8.17 Floor and wall clearances between sump and suction bell
(After Jamandre, 1977)

8.6 Power requirement

The capacity or discharge of a pump, its efficiency, and the total dynamic head are the necessary information in determining power requirement. The pump discharge is determined from the flow requirement of the fish farm, the efficiency at a given discharge rate and head from the manufacturer's pump characteristic performance curves (for different kinds of pumps), and the total dynamic head by obtaining the necessary measurement as implied in the example problem and Fig. 8.12.

The brake horsepower is computed by the formula:

Where:Bhp =the brake horsepower that must be supplied by the prime mover to the pump to operate it at the required capacity and given efficiency.
 E =pump efficiency
 Q =discharge of pump in gallons per minute
 TDH =total dynamic head in feet
 3 960 =a constant of conversion

When the prime mover is an engine, it should be operated at 75 percent of its full load capacity. The required engine horsepower is therefore:

8.7 Selection of prime mover

Available prime movers of pump to choose from are:

(a) Engine. Internal combustion engine are run either by gasoline or diesel fuel. In deciding which to use between the two, consideration should be given to the initial engine cost, fuel cost, cost and availability of spareparts, and availability of repair mechanic in the area. Since diesel engine has higher initial cost than the gasoline, it is advisable to use it more hours per season than the latter in order to be economical.

The brake and engine Hp in the preceding problem will be:

(b) Electric motor. This is preferable if electricity is cheap and no frequent power interruptions occur. The advantage of electric motor is its long life, dependability, low maintenance cost, quiet and easy to operate and it is usually taken as 100 percent efficient.

If an electric motor is required to drive the pump in the preceding example problem, the needed Hp will be only 33 Hp.

8.8 Accessories and other devices

There are some accessories and devices that are important in the operation of pumps. These are as follows:

  1. Foot valves. Centrifugal pumps usually need foot valves in order to hold water during priming. This valve is not necessary in propeller, turbine pumps and self-priming pumps.

  2. Gear drive. One of the accessories in propeller pumps is the “gear drive”. This device does three things (Fig. 8.18): (i) change the direction of drive from vertical to horizontal for attachment of other prime movers; (ii) change input rpm to the desired or designed pump rpm; and (iii) provides alternative horizontal drive where there is already a vertical electric motor driving the pump. The gear drive, however, may cost as much as the pump itself.

  3. Fig. 8.18

    Fig. 8.18 Illustration of the function of a gear drive
    (After Jamandre, 1977)

  4. Cross joints and shafts. These may be used instead of the gear drive. This is done by installing pump in a slanting position (Fig. 8.19).

  5. Hydraulic driven pump. This is a system where the prime mover drives a hydraulic pump and the high pressure transmitted through hydraulic hoses drives a hydraulic motor attached to the impeller. One advantage of this system is that it becomes flexible as it eliminates the need for long drive shafts that need careful alignment (Fig. 8.20). It also eliminates the shaft as an obstruction in the pump column.

  6. Fig. 8.19

    Fig. 8.19 Cross joint and shaft assembly
    (After Jamandre, 1977)

  7. Pump columns. Careful consideration on the kind of material for pump column in brackishwater is important to avoid or minimize corrosion. Pump columns are usually made of cast iron and not steel because it is less affected by saltwater. There are pumps, however, that have columns made of stainless steel; some have thick-coating of zinc making it durable and rust-resistant. Fiberglass columns, wood and concrete are also available in some pumps.

Fig. 8.20

Fig. 8.20 High discharge hydraulic driven pump
(After Jamandre, 1977)

8.9 Pump installations in certain conditions

  1. Vertical and slanting installations. These are illustrated in Figs. 8.19, 8.20 and 8.21.

  2. Fig. 8.21

    Fig. 8.21 Types of propeller pump installations (After Jamandre, 1977)

  3. Installation where pond may be filled or drained irrespective of tidal conditions. Jamandre (1977) suggested and designed propeller pump and open channel combination, and system of gates valves to flood and drain ponds at will.

Figure 8.22 illustrates the pump installation and elevation of bottom of two adjacent channels provided with system of gates for checking the passage or entry of tidal water. The discharge pipe can discharge water in either direction in the channel through the manipulation of the gates.

In Fig. 8.23 the pump can water the pond with valves 1 and 3 close, and 2 and 4 open. With valves 1 and 3 open, and 2 and 4 closed, the pump can drain the pond.

Fig. 8.22

Fig. 8.22 Set-up for filling and draining pond water irrespective of tidal level (After Jamandre, 1977)

Fig. 8.23

Fig. 8.23 Gate valve system for filling and draining fishpond regardless of tide level
(After Jamandre, 1977)

Being able to fill and drain the pond at will offers several advantages:

  1. Enables harvesting of crop when prices are good while other pond owners have to wait for appropriate tidal condition.

  2. Drain low oxygen water and replenish with fresh and highly oxygenated water.

  3. Enables greater stocking densities or intensive culture in ponds.

8.10 Economics of pump use

The use of pumps in coastal aquaculture as an alternative solution to some of the problems associated with tidal fishponds is becoming popular. Although some of these problems could be remedied by proper pond construction and efficient management, they are not entirely eliminated and the costs involved significantly affect the financial viability of the fishpond enterprise. Probably, the use of pumps is a better alternative. However, before a decision is made or whether to use pumps or not, a close examination of the costs associated with their use should be made.

Information regarding the use of pumps in brackishwater fishpond culture is very scarce. One such study made in Malaysia (Gedney, Shang and Cook, 1982) offers significant information. Designs for both tidal and pumped-operated pond culture systems were prepared and a comparative cost analysis of expense items which are different between the two systems were made. These items are interest and principal payment of pond construction and pumping, maintenance and land. Results of this particular study showed that a pump-operated system is more economical than a tide-operated system because of the savings in costs of construction and operation.

The specific preliminary conclusions of the study identified the following advantages of pump-operated system over tide-operated system:

  1. Less construction cost because of smaller dikes and reduced time of construction.

  2. Better land utilization due to greater effective water area and use of lots otherwise not feasible under a tidal fishpond system.

  3. More efficient management which allows for flexibility in filling, draining and harvesting and easier pond maintenance.

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