PEDAL POWERED WATER PUMP

PEDAL POWERED WATER PUMP

Water is a very essential commodity for the survival of mankind. Apart from being used for drinking, it is also used as a source of energy and as a mode of transport. Unfortunately, it is not always readily available. While almost 70% of the earth’s surface is covered by water, fresh water accounts only for 2.5% with the rest being ocean based and saline. Add to this the fact that of the 2.5% fresh water, only 1% is easily accessible in the form of rivers and other fresh water bodies whereas the rest is trapped in snowfields, glaciers or as underground water and you realize that it is important to device mechanisms to get it from places that would normally not be possible. These places include boreholes and shallow wells.

A pedal powered pump is one of these mechanisms as it enables us to draw water from shallow wells, especially in areas where electricity is either non-existent or is too costly to afford.

Background information

A pump is basically a device which uses mechanical action to move fluids and in some instances slurries. Pumps fall into three main groups based on the method used to move the fluid. These groups are gravity, lift and displacement. To move the fluid the pumps take up energy in one form or the other including electricity, wind power and manual labour.

Pedal powered water pumps falls into the manual labour category and are mostly applied in rural areas to pump water either for domestic use or for irrigation.


A good example of a pedal powered water pumps is the Kickstart’s Super Moneymaker pump shown in Figure 1.
Figure 1: Pedal powered water pump [1]
 This is basically a lift pump with a piston and a check valve on each side of the pedals. On pedaling, an alternate up and down movement of the plunger occurs with the upward movement causing a negative pressure or rather a vacuum to occur. This causes a check valve at the bottom to open, drawing water inside the chamber. During the downwards movement, positive pressure is created closing the check valve and opening a rubber flap allowing the water to flow out. This can be then channelled for the intended use.

In this article we will describe how you can make a pedal powered water pump by redesigning a bicycle, something that is frequently used, and including a centrifugal pump.

How to build a pedal powered water pump

The first thing is to acquire a normal bike which then needs to be modified so as to double up as a pedal powered water pump. Since we don’t want to lose the transportations capabilities of the bike, it is designed to have two modes, a transportation mode and a pumping mode. The overall design is composed of the following parts;

1. The supporting frame

A triangular shaped supporting frame can be designed using a CAD software as shown in Figure 2. It can then be fabricated using steel and incorporated to the bicycle axle.

Figure 2: Cad design of a pedal powered water pump [2]

To fabricate the supporting frame, a few tools will be needed including a chop saw for cutting the pieces to size, an arc welding machine for welding the frame, a bench grinder to smoothen the welded joints and a drill press to bore the slots used to attach the supporting frame to the rest of the bicycle. Modifications can be done depending on the available materials and equipment. As mentioned earlier, the supporting frame is designed such that it can be flipped up to act as a rack when the bicycle is in the transportation mode. This is illustrated in Figure 3.

Figure 3: Pedal powered water pump in pumping mode [2]


2. Centrifugal pump

This should be sized based on the exact purpose of the pedal powered pump. Specifications of the required head, intended flow rate and the depth of the water source are needed in order to accurately specify the suitable pump. A suggestion would be a pump with approximately a 35m head, 350 W power and a flow rate of 40 litres per minute. The pump then needs to be incorporated in the rear end of the bike with its armature used as a roller which is friction driven by the tyre at the rear end. This setup helps to rotate the pump at the required speed.

Fabrication, testing and optimization

After fabrication of the pump as shown in Figure 4, the next phase is testing and making modifications to optimise the performance. Among the parameters to be tested include the depth up to which the pump can retrieve water simply called the suction head as well as the maximum height to which the pump can lift the water simple called the water head.  From this actualised prototype, it was possible to achieve a water head of over 20m and from over 7 metres below. At ground level, it was possible to achieve a water flow of around 30 litres per minute which compare favourably to the one of the original centrifugal pump. This, with only pedal power operation, is fantastic!

Figure 4: Fabricated pedal powered water pump [2]

Precautions

It is important to ensure that there are no leakages in the system as these greatly lower the water pressure or increase the friction in the pipe. This consequently results in poor results.

Advantages of the pump

  1. It can be operated even in the remotes parts of the world since it does not require electricity. This means that it does not result in environmental pollution as is the case with fossil fuel powered pumps and generators. It also exempts the user from the effects of rising energy costs.
  2. It can be build using locally available materials and hence minimize on cost.


References/ Important links
1. https://c2.staticflickr.com/2/1101/533783075_21150004c2_b.jpg
2. Leary, J. (2010, February). Putting Research into Practice: From a Steel City Drawing Board to the Heart of the Maya. In The University of Sheffield-EWB-UK National Research Conference.

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