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<center>[[File:New Dawn Engineering Treadle Pump.jpg]]
<center>[[File:New Dawn Engineering Treadle Pump.jpg]]


<b>Figure 5: New Dawn Engineering Treadle Pump (New Dawn Engineering, 2009)</b><center>
<b>Figure 5: New Dawn Engineering Treadle Pump (New Dawn Engineering, 2009)</b></center>


The equation that dictates the mechanical advantage of a lever is:
The equation that dictates the mechanical advantage of a lever is:

Revision as of 09:16, 16 April 2010

Template:425inprogress


Treadle Pump Optimization Project

The treadle is a very simple design that is used to produce rotary or reciprocating motion in a machine, which dates back to Thomas Saint’s original sewing machine design he had patented in 1790 and earlier. This basic component can be used in many simple machines, including grinders and pumps. A treadle pump is defined as a foot operated single acting double cylinder piston pump for low lift irrigation (New Dawn Engineering, 2009). Pumping is activated by stepping up and down on the treadles to drive the attached pistons, creating suction in the cylinder that draws groundwater to the surface (International Development Enterprises, 2010). This water can be sourced from a river or well and is used for irrigating farmers’ fields or to store water in a container for later use. Treadle pumps have been used in many countries worldwide such as Ghana, Zambia (Engineers Without Borders Canada), Swaziland, Kenya (New Dawn Engineering, 2009), Bangladesh, Nepal, India, Cambodia and Myanmar (Cooper Hewitt , 2006), as well as many others. Presently, 84 manufacturers now produce treadle pumps and 1.4 million have been sold to small plot Bangladeshi farmers since 1985 (International Development Enterprises, 2010). Figure 1 below shows 12 pump designs and their origins, maximum volumetric input, features and cost.

MECH 425 - Sample of treadle pumps in Africa.jpg Figure 1: Sample of treadle pumps found in Africa (Food and Agriculture Organization, UN, 2002)

Engineering Principles

How They Work

A treadle pump is a basic cylinder-based pump: it comprises a cylinder fitted with a piston and some means of pushing the piston up and down (Kay, 2000). A pipe connects the water source to the pump, where a non-return valve is fitted to allow water to flow in and prevent it from flowing out. The piston itself must have a snug fit inside the cylinder in order to create a vacuum to draw water in. The piston itself contains a similar valve such that, when it is forced downward by the treadle, water flows through the piston from the space below to the space above it. The opposite then occurs when the piston is lifted: the valve closes, forcing the water above the piston to the outlet all the while drawing in water from below. Various types of non-return valves are used, including rubber flaps, swinging gates and poppet valves (Development Technology Unit, 1991). An illustrated version of this is shown in Figure 2. In the past, these pumps were hand-operated and quite inefficient, as the effort required to lift small amounts of water was significant. Using the larger muscles in one’s legs and two pistons has greatly increased the efficacy of this machine. The treadles are joined, either by a rope passing over a pulley, a chain and rocker system, or a centre shaft (Kedge, 2001). This connects the two pistons as well and associates the upward motion of one treadle/piston with the downward motion of the other.

MECH 425 - Treadle pump operating principles.jpg Figure 2: Treadle pump operating principles (Kedge, 2001), adapted from(Kay, 2000)

This pump currently has two monikers, each defined by the outlet portion of the pump. If the water is discharged to an open channel for irrigation, it is termed a suction pump. Suction pumps are designed for lifting large volumes of water from relatively shallow water sources (Kedge, 2001). If the water is discharged to a pipe, it is termed a pressure pump. In the pressure pump, another valve is used at the discharge end, maintaining pressure in the pipe that can be used to drive sprinklers or drippers or deliver water to a header tank (Kay, 2000).

Hydraulics

A vacuum is created when the piston moves up in the cylinder and atmospheric pressure is then used to propel the water into the cylinder. Both temperature and pressure have an effect on the atmospheric pressure and the suction lift that can be obtained. In centrifugal pumps it is common to refer to the NPSHa, which is the net positive suction head available. In the treadle pump case, since the pump is located above the water source, the difference in elevation between the water and the pump is taken as positive and NPSHa decreases as the difference increases. The equation for calculating NPSHa is (NPSH - Net Positive Suction Head, 2005):

Net Positive Suction Head a.jpg

Where: P_atm= atmospheric (or absolute) pressure;

γ= specific weight of the fluid;	
h_z= vertical distance (elevation) between the surface of the water and the pump;

∆h_f= head loss due to major and minor losses in the suction pipe, valves and fittings; P_v= vapour pressure of the fluid; and The equation for calculating the specific weight of the fluid (water) is (Density, Specific Weight and Specific Gravity, 2005): γ= ρg Where: ρ= density of the fluid; and g= acceleration of gravity. NB: Density varies with altitude, acceleration of gravity with latitude.

Statics

The force applied by the person on the treadle is based on the lever principle. Operators of the pump can move their position on the treadles to gain a mechanical advantage while maintaining a comfortable applied force and steady cadence (Kay, 2000). There are three types of levers: in the class I lever, the applied force and the load are on either side of the fulcrum, while the class II lever the load is positioned between the applied force and the fulcrum and the class III lever has the applied force positioned between the fulcrum and the load. The Swiss Concrete Pedal Pump (SCPP), developed by W-3-W Association Switzerland, is prime example of a class I lever (Figure 3). Tests conducted at the Lucerne School of Engineering and Architecture (HTA) showed a very impressive 65% energy efficiency and a maximum discharge volumetric flow rate of 80 L/min (with an average human input of 60 – 65 W and a suction lift of 3 m) (Water for the Third World, 2006).

Swiss concrete pedalpump.jpg Figure 3: Image of a Swiss concrete pedal pump (Water for the Third World, 2006

Another example of a class I lever treadle pump is the original version developed in Bangladesh in the early 1980’s, pictured below (Figure 4):

Bangladesh treadle pump.jpg Figure 4: An example of a class I lever in the Bangladesh treadle pump (International Development Enterprises, 2010)

Note that if the operator were to switch sides (i.e. pump from the right of the image), Figure 4 would then become an example of a class II lever in action.

A good example of a class II lever treadle pump is the New Dawn Engineering Treadle Pump (Figure 5):

New Dawn Engineering Treadle Pump.jpg Figure 5: New Dawn Engineering Treadle Pump (New Dawn Engineering, 2009)

The equation that dictates the mechanical advantage of a lever is:

MECH 425 - Mechanical advantage.jpg

Where: l= the distance between the force applied and the fulcrum; and r= the distance between the load and the fulcrum.

When the foot force of an operator is directed precisely on top of the pistons as shown in Figure 6-1 below, this force is transferred directly to the pistons. As the caption to the right of the image demonstrates, this is equal to a mechanical advantage (MA) of 1. However, as the operator moves along the treadles, an MA can be obtained in one of two ways: Figure 6-2 shows an increased distance between the applied force and the fulcrum (class II lever), hence an MA greater than 1 and a mechanical advantage gained in force. Figure 6-3 shows a decrease in the distance between the applied force and the fulcrum (class III lever), hence an MA less than 1 and a mechanical advantage gained in speed and range of motion. What this means is that a light operator, such as a child, could operate the pump standing farther away from the pivot (to take advantage of the extra leverage), and a heavy, or strong operator could move closer to the pivot with both being comfortable pumping positions (Kay, 2000).

Mechanical advantage has a direct impact on the stroke length of the piston: an MA greater than 1 means a decrease in stroke length while an MA less than 1 results in an increase in stroke length. Taking advantage of MA’s greater than 1 allows more force to be applied to the piston, hence greater pumping pressures can be achieved, but this is at the expense of volumetric flow because of the reduced piston stroke length (Kay, 2000).

MECH 425 - Using mechanical advantage.jpg Figure 6: Using mechanical advantage (Kay, 2000)

Bibliography

Cooper Hewitt . (2006). Bamboo Treadle Pump. Retrieved April 4, 2010, from Design for the Other 90%: http://other90.cooperhewitt.org/Design/bamboo-treadle-pump

Development Technology Unit. (1991). The Treadle Pump: Working Paper No. 34. Development Technology Unit, Department of Engineering. Coventry: University of Warwick.

Engineers Without Borders Canada. (n.d.). The Treadle Pump. Retrieved April 4, 2010, from Engineers Without Borders Canada: http://www.ewb.ca/en/whatwedo/overseas/projects/treadle.html

Food and Agriculture Organization, United Nations. (2002, January). Briefing Note on Treadle Pumps. Retrieved April 4, 2010, from Water Conservation and Use in Agriculture: http://www.wca-infonet.org/servlet/BinaryDownloaderServlet?filename=1016103720274_Treadlepump_brief.pdf&refID=18556

International Development Enterprises. (2010). Treadle Pump. Retrieved April 14, 2010, from International Development Enterprises: http://www.ideorg.org/OurTechnologies/TreadlePump.aspx

Kay, T. B. (2000). Treadle pumps for irrigation in Africa. International Programme for Technology and Research in Irrigation and Drainage. Rome: Food and Agriculture Organization of the United Nations.

Kedge, C. (2001). The Introduction of Treadle Pumps into South Africa. (p. 8). Johannesburg: SABI.

New Dawn Engineering. (2009). Treadle Pump for Low Lift Irrigation. Retrieved April 4, 2010, from New Dawn Engineering: http://www.newdawnengineering.com/website/pumps/treadle/

Thomas, T. H. (1993). The Performance Testing of Treadle Pumps. Development Technology Unit, Department of Engineering. Coventry: University of Warwick.




Treadle_pump

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