WCDE-00088-02 BMEIA Hydram Pump Design 100420

BMEIA HYDRAM PUMP DESIGN Hydram Pump Background Information

David Effa and Dr. Abiy Awoke

WCDE-00088-02 Revision 100126

David M. Effa of the Waterloo Cases in Design Engineering (WCDE) Group and Dr. Abiy Awoke of BMEIA prepared this design case study for

classroom use. The authors do not intend to illustrate either effective or ineffective handling of an engineering situation. The authors may have

disguised certain names and other identifying information to protect confidentiality.

The Waterloo Cases in Design Engineering Group prohibits any form of reproduction, storage or transmittal of this document without its written

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permission to reproduce materials contact Waterloo Cases in Design Engineering c/o Department of Mechanical Engineering, University of

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Introduction to the Hydram Pump

The Hydram pump, depicted in Figure 1, is an automatic

water pumping device that utilizes the energy contained in a

flow of water running through it to lift a smaller volume of

this water to a higher level. The phenomenon exhibited

within the Hydram pump is a pressure surge, which develops

when a moving mass of water is suddenly stopped. This

pressure surge generated by the main flow of water is used to

drive a smaller volume of water over long distances. In this

way, water from a spring or stream in a valley can be pumped

to a village or irrigation scheme on the hillside without an

external power source. This ensures low running costs and no

significant harm to the environment. Hydram pumps are

simple, reliable and require minimal maintenance [1].

The basic principle behind Hydram pump function is the use

of a large amount of water falling a short distance to pump a

small amount of water to a higher elevation. Typically, only 2

to 20 percent of the water flowing through a Hydram pump

system will actually be delivered to the storage tank or

trough. The remainder is overflow and is directed back into

the stream.

Figure 1:- Hydram Pump [4]

Hydram pumps have low pump efficiency (less than 66%) and require a suitable geographical area for

implementation [2]. In the right location, however, the Hydram pump is able to pump water autonomously,

with no external energy input, for years, with minimal maintenance. This makes Hydram pumps suitable for

communal water supply and irrigation in rural areas with limited access to power but suitable topography and

hydrology. In recent years, an increased interest in renewable energy devices and a heightened awareness of

the need to match technological solutions to the needs of particular markets in developing countries, such as

water supply and management, have prompted a reappraisal of Hydram pumps.

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BMEIA HYDRAM PUMP DESIGN WCDE-00088-02

The main advantages of the Hydram pump can be summarized as follows:

The Hydram pump is simple in construction and operation. High reliability means few maintenance

requirements.

It does not incur any running costs; as it utilizes the energy of freely available water, no fuel or

electricity is required.

It does not produce any pollution.

Pumping only a small proportion of the available water flow limits the environmental impact.

Automatic, continuous operation requires no supervision or human input.

It has only two moving parts, the waste valve and the delivery valve, as shown in Figure 2. Both of

these are lubricated by the water itself, thus no separate arrangement for lubrication is required.

The main limitations are as follows:

Hydram pump use is limited to hilly areas with year-round water sources.

It pumps only a small fraction of the available flow and therefore requires source flows significantly

larger than the actual water delivered.

It is limited to small-scale applications, usually up to 1kW, but this depends on economic and other

considerations.

Figure 2 - Hydram pump main components

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Environmental assessment for Hydram pump applications

The use of a Hydram pump requires the availability of a suitable and reliable supply of water, as well as a

sufficient working fall to drive pump operation. The supply can be any source of flowing or stagnant water

such as a spring, stream, river, lake, or dam, or even a pond fed by an artesian well. A small Hydram pump

requires a supply flow of at least 5 to 25 litres per minute, whereas a very large Hydram system may need as

much as 750 to 1500 litres per minute [2]. Environmental assessment is typically performed in two stages: a

preliminary assessment to locate potential sites and a full survey to select the best option. The preliminary

survey involves the following steps:

Consulting relevant maps and hydrological studies;

Traveling to potential sites to make a preliminary assessment and consult with local people regarding

their needs and the suitability of the water source for their application; and

Selecting one or more sites with high potential for a more detailed survey.

The full survey of selected sites must be sufficiently detailed to provide most of the information necessary for

accurate system design. Some of this information is indicated in Figure 3 and includes the following:

i. Water source flow (Q) - The data must reflect the minimum flow of water in a normal year, which

means this measurement must be taken during the dry season. To ensure the figure represents a typical

minimum flow, local people should be consulted about flow patterns experienced over recent years.

Some indication of maximum expected flows is also necessary.

ii. Drive head (H) - The maximum possible drive head of the site or the average angle of the slope below

the water source should be measured.

iii. Delivery head (Hd) - The height from the water source to the expected point of delivery should be

measured.

iv. Water requirement (Qs) - This should be estimated with reference to the population to be served

(allowing for growth) or the area of land to be irrigated.

v. Distance over which the working fall (Ldp), from the drive tank to the hydram pump, should be

obtained.

vi. Length of delivery pipe from the Hydram pump to the delivery site (Lps) should be estimated.

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Figure 3 Schematic of Hydram pump system installation

Hydram Pump Working Principles

All Hydram pumps work on the principle of momentum, which is controlled by a cycle set up by the

interaction of two valves in the pump. Figure 2 shows the basic components of a Hydram pump and Figure 4

shows its operating cycle. When the waste valve is opened, water begins to flow down the drive pipe and

through the waste valve as shown in Figure 4a. The water in the drive pipe starts to flow under the force of

gravity, picking up speed and kinetic energy until the waste valve is forced to close. Indeed, as the flow

increases, it reaches a speed where the drag force is sufficient to start closing the waste valve. Once the waste

valve has begun to move, it closes very quickly as shown in Figure 4b.

The water flowing in the drive pipe has considerable momentum which has to be dissipated. Therefore, for a

fraction of a second, the water in the body of the pump is compressed causing a large surge in pressure. This

type of pressure surge is known as water hammer. As pressure rises in the pump, the delivery (discharge)

valve opens and some water flows into the pressurized air vessel above water level. The air inside the air

vessel cushions the hydraulic pressure shock when the waste valve closes. It also improves the pumping

efficiency by allowing a more constant flow through the delivery pipe.

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Figure 4- Hydram pump operating sequence

In the next phase, Figure 4c, the water pressure above the delivery valve overcomes the spent momentum

below it, forcing the delivery valve to close again. The water that made it past the delivery valve, Figure 4d, is

then forced by the extra air pressure up the delivery pipe. The recoil also sucks a small amount of air in

through the air valve. The air sits under the delivery valve until the next cycle, when it is pumped with the

delivery water into the air vessel. This ensures that the air vessel stays full of air. Since the momentum of the

water coming down the drive pipe has stopped, the waste valve falls open, allowing the water to flow down

the drive pipe again as in Figure 4d, starting the cycle over again.

The pumping cycle happens very quickly, typically 25 to 300 times per minute. The frequency of the cycle

can be adjusted by changing the length of the waste valve stroke. A longer stroke produces a lower frequency.

This means more of the water supply flows to and through the pump and more is pumped up the delivery pipe.

The stroke is adjusted to appropriately restrict the amount of water used in accordance with the amount

available, or if supply is unlimited, to regulate the amount delivered to match the amount needed. Generally,

during each pumping cycle, only a very small amount of water is pumped. However, with cycle after cycle

continuing over 24 hours, a significant amount of water can be delivered.

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Hydram pump design

Although Hydram pumps come in a variety of shapes and sizes, they all have the same basic components, as

shown in Figure 2. The main parts of the Hydram pump are the Hydram body, waste valve, air valve, delivery

valve, air vessel (chamber) and relief valve. Hydram pumps have a cyclic pumping action that produces their

characteristic beat during operation. Before designing or selecting a Hydram pump, several design factors

must be known, including vertical fall (H), lift (Hd), available source flow (Q), required water flow ( ), drive

pipe length (L) and delivery pipe length (l). Once this information has been obtained, a preliminary

calculation can be made to see if the amount of water needed can be supplied by a Hydram pump. Hydram

pump design information is listed in Appendix A.

Hydram pump efficiency

Hydram pump efficiency can be expressed in two ways. The first expression, known as the D'Aubuisson

efficiency ratio, gives the efficiency of the Hydram as a machine [2]. This is the ratio between the input

energy of the Hydram and its output energy. The second expression, known as the Rankine formula for

efficiency, considers the Hydram as a hydraulically operated pump [2]. This takes into account the difference

in elevation between the water surface in the supply channel and the delivery point as the actual delivery head.

i. DAubuissons Efficiency Ratio

(1)

Qw is the quantity of water escaping through the waste valve (litres/min)

Qs is the quantity of water supplied by the ram (litres/min)

H is the fall or height of the source above the Hydram (m)

Hd vertical distance or elevation that the water will be raised (m)

DAubusson efficiency of the Hydram pump

A more precise expression of the efficiency of the Hydram, taking into account the head loss due to friction

in the supply and delivery pipes, is:

(2)

Where

hsf is head loss due to friction in supply pipe (m)

hdf is head loss due to friction in delivery pipe (m)

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ii. Rankines Formula for Efficiency

(3)

Using equation 1, the relationship between pump output and water source input can be expressed as [2]

(4)

Where

Q is the required flow rate in litres per minute [litres/min], which is the sum of the waste

valve and supplied water rates

The efficiency of a Hydram pump varies inversely to the ratio between the delivery head ( ) and the supply

head ( ), also called magnification ratio [2]. Hydram pump manufacturers, including BMEIA, have

developed a catalogue listing the efficiency of the Hydram pump as a function of the magnification ratio.

Most Hydram pumps operate at the best efficiency (66% to 70%), if the magnification factor is limited to 4

[3]. Table 1 solves this formula for Hydram pumps with a magnification ratio of 4 (66% efficiencies) and a

water supply of 1 litre per minute across varying working fall and lift heights. For supplies greater than 1

litre/minute, performance results can be obtained by multiplying the Hydram efficiency factors provided in

Table 1 by the number of litres supplied per minute. For example, if the working fall is 6m and the vertical

lift above the Hydram is 20m, from Table 1 a factor of 282 can be found. For every litre per minute of water

flowing into the Hydram, the amount delivered will be this factor in litres per day. Therefore, if 10 litres per

minute flows into the Hydram then (10 x 282) 2820 litres per day will be delivered. Alternatively, if the total

daily requirement of water is known per day, then this number is divided by the efficiency factor to find the

amount of water in litres per minute that must be supplied to the Hydram. For example if 20,000 litres per day

was required, then 20,000 282 = 70 litres per minute would have to be delivered to the Hydram.

Hydram pumps must be designed to produce a required flow rate while generating enough pressure to lift the

water to the desired elevation. In most cases, the fall from the water supply source to the Hydram pump must

be at least 50 cm and the minimum flow of water needed is roughly 1-2 litres per minute (lpm). The optimum

length of the drive pipe is 5 to 12 times the vertical distance between the source and the pump or, 500 to 1000

times the diameter of the delivery pipe, whichever is less [5]. This length of drive pipe typically results in a

period between pulses of 1 to 2 seconds. The drive pipe is ordinarily straight but can be curved or even wound

in a spiral. The main requirement is that it is inelastic, strong and rigid; otherwise, efficiency would be greatly

diminished.

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Table 1- Hydram performance data for a supply of 1 litre/minute

Working Fall (m) Lift- Vertical height to which water is raised above the Hydram (m)

5 7.5 10 15 20 30 40 50 60 80 100 125

Litres delivered over 24 hours

1.0 144 77 65 33 29 19.5 12.5

1.5 135 96.5 70 54 36 19 15

2.0 220 156 105 79 53 33 25 19.5 12.5

2.5 280 200 125 100 66 40.5 32.5 24 15.5 12

3.0 260 180 130 87 65 51 40 27 17.5 12

3.5 215 150 100 75 60 46 31.5 20 14

4.0 255 173 115 86 69 43 36 23 16

5.0 310 236 155 118 94 71.5 50 36 23

6.0 282 185 140 112 93.5 64.5 47.5 34.5

7.0 216 163 130 109 82 60 48

8.0 187 149 125 94 69 55

9.0 212 168 140 105 84 62

10.0 245 187 156 117 93 69

12.0 295 225 187 140 113 83

14.0 265 218 167 132 97

16.0 250 187 150 110

18.0 280 210 169 124

20.0 237 188 140

References

[1] Dr. Tessema, Abiy Awoke Hydraulic Ram Pump System Design and Application" ESME 5th Annual

Conference on Manufacturing and Process Industry, September 2000

[2] Teferi Taye, "Hydraulic Hydram Pump", Journal of the Ethiopian Society of Mechanical Engineers, Vol.

II, No. l, July 1998.

[3] Jeffery, T. D., "Hydraulic Hydram Pumps - A Guide to Hydram Pumps Water Supply

System", Intermediate Technology Publications, 1992.

[4] http://www.greenandcarter.com/

[5] Krol, J.: The automatic hydraulic Hydram . Inst. Mechanical Engineering Proc. Vol. 165 (1951) No. 64,

pp. 53/73.

[6] Dnadhar, M.M and Sharma, K.N, 1979, Water Power Engineering, Vikas Publishing House Pvt. Ltd.

India.

[7] David, J.P. and Edward, H.W., 1985, Schaum's Outline of Theory and Problems of Fluid Mechanics and

Hydraulics, SI (Metric) Edition, McGraw-Hill Book Company, Singapore.

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APPENDIX A Important information for Hydram pump design

Table 1 - Range of Drive Pipe Lengths for Various Pipe Diameters

Drive Pipe Size (mm) Length (meters)

Minimum Maximum

13 2 13

20 3 20

25 4 25

30 4.5 30

40 6 40

50 7.5 50

80 12 80

100 15 100

Table 2 - Range of Drive Pipe Lengths for Various Pipe Diameters

Hydram Size 1 2 3 3.5 4 5 6

Pipe Size (mm) 32 38 51 63.5 76 101 127

Table 3 - Hydram Capacity by Manufacturer's Size Number

Size of Hydram

1 2 3 3.5 4 5X 6X 5Y 6Y

Volume of Drive Water

Needed (liters/min)

7-16 12-25 27-55 45-96 68-137 136-270 180-410 136-270 180-410

Maximum Lift (m) 150 150 120 120 120 105 105 105

Table 4 - Sizing the Delivery Pipe

Delivery Pipe Size (mm) Flow (litres/min)

30 6-36

40 37-60

50 61-90

80 91-234

100 235-360

Table 5 Daily Water Requirements

Livestock (drinking) Gallons/animal/day

Milking cow 25-45

Dry cow 12-30

Calf 6-12

Beef animal 1.5/100 lbs. weight

Hog 4

Horse 10-15

Sheep 2

100 Chickens 4-5/100 birds

100 Turkeys 18/100 birds

Source: Cooperative extension Service/The University of Georgia College of Agriculture and Environmental

Sciences/Athens

WCDE-00088-02 BMEIA Hydram Pump Design 100420

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