4. METHODOLOGIES
4.3.7 M echanical efficiency
The mechanical efficiency of a treadle pump can be approximated as:
l1mech ;;;;
Win-Wf
Equation 6
where W;o is the input power and Wt, the power required to overcome friction. Power is measured as the product of force and speed. Since the speed is the same for both useful forces and for friction forces,
Tlmech;;;;
Fin - Ff
Equation 7
provided both input force, F;o, and friction force, Ft, are measured at the same place (Thomas, 1993).
The input force was measured at the end of each treadle where the operator stands.
The pump was connected to a four metre head and the weight to move the treadles was recorded. The friction force was then measured at the same point on the treadle with the pump head reduced to zero.
The positioning of an operator relative to the pistons of a treadle pump is based on the lever principle. When an operator is standing on the treadles immediately above the pistons, the pushing force is directly transferred to the pistons. An operator's downward force of say 300 Newtons (30 kilograms) thus transfers directly a force of 300 Newtons to the piston. If the operator moves away from this position and increases the distance from the pivot point of the treadles, a greater force can be applied to the pistons. The converse is also true. If the operator moves to reduce the distance from the pivot to 0.8 metres, the downward force on the piston reduces to 240 Newtons. This ratio of the distance of the operator and the piston from the pivot point is known as the mechanical advantage (Kay and Brabben, 2000).
4.3.8 Sustainable flow and heads
The operators were each asked to treadle for ten minutes at various combinations of suction heads and delivery heads for the pressure pumps and various suction heads
for the suction pumps. The heights were determined according to the different pumps as not all the pumps could pump the same heads. The height of the table, 0.8 metres, was included in the suction heads for the suction pumps. The number of strokes were counted and recorded after each minute of pumping. The operators'
heart rates were also recorded every minute. Table 5 shows a summary of the various heads that were used.
Table 5. Suction and delivery head combinations, in metres, used for tests.
PUMP Suction 1 2 3 4 5 6
PLATFORM Delivery 2 6 2 4 2 4
Total 3 7 4 6 5 8
SWAZI Delivery 2 6 2 4 2 5 1 2
Total 3 7 4 6 5 8 5 6
APPROTEC Delivery 1 4 1 3 4 7
Total 3 6 5 7 10 13
SWISS Suction 2.8 3.8 5.8
KB Suction 2.8 3.8 4.8
IDE suction 2.8 3.8 5.8
4.3.9 Pump efficiency
The efficiency of a treadle pump can be defined as the ratio of the output power and the input power. This was calculated using the following equation:
_ ---"p"'. go:.' Q.:oc.:.' H=--
llpump =
operator power Equation 8
where, p is the density of water, 1000 kg/rn', g is the acceleration due to gravity, 9.81 m/s2, Q is the average flow obtained during the ten minutes of pumping, m3/s, and H is the total head that was pumped, m. The operator input power was determined using equation 5 for the Swazi pump and the calibration curves obtained from the heart rates for all the other pumps.
4.3.10 Adjustments during pumping
The Platform pump required adjustment before it would operate. The reinforced helix pipe on the suction side was changed to 50 mm, class 3 potyethylene pipe and reclamped with wire clamps. This was because the pump was continuously drawing in air at the jOints, decreasing its performance. The valves were not exactly 50 mm in diameter and insulating tape was wound around them to increase their diameter before the pipe was reconnected. The connections were still not completely airtight after the adjustment and this had an impact at high heads. Air was also being drawn through the o'ring seal at the top of the cylinder. Silicon was placed around the piston rod hole to attempt to stop this. The pump was set on the middle setting for all three operators. A frame was built out of scrap metal to use as a handle for the Platform, Swiss, KB and IDE pumps. The height of the frame could be adjusted according to the operator's height and the different heights of the pumps.
The leather cups on the pistons of the Swazi pump were slightly small and the water would therefore not stay on the top of the pistons during pumping. The water had to be constantly monitored and topped up. The cups were greased in an attempt to seal the gaps between the pistons and cylinders. The problem appeared to improve as
the pump was used more, because the leather started absorbing the water and therefore swelled. A steel bar was placed through the handle to decrease the maximum stroke length as the pistons would sometimes rise too far, spilling the water over the tops of the cylinders and sometimes popping out of the cylinders. The pump was difficult to prime at higher suction heads.
The Approtec pump always started easily once a little water had been poured into the top of the cylinders. It could not hold it's prime at a suction head of one metre and delivery head of two metres. Water had to be poured into the cylinders about once a minute. This problem only exists at lower heads and is mentioned by the manufacturers in the user manual. Water is able to flow between the cylinders and this helped with priming. The Approtec pump was tested twice, once with the foot valve that came with the pump and once with a brass foot valve, used for all the other pumps. The results presented are those obtained with the brass valve, except for the section where a comparison is made.
The Swiss pump was also tested twice. After the first day of testing it was found that the bicycle spokes holding the rubber flap valves had not been replaced in the correct positions and were no longer holding the valves in place. The 12 mm diameter shaft holding the treadles in place bent after the first days testing, and was replaced for the second tests with a 16 mm diameter shaft.
10 kilogram weights were used for the IDE pump for operators Band C. Two 20 kilogram weights were used for operator A.
4.4 Treadle Pump Quantitative Assessments: Field Tests
A few of the imported treadle pumps that were tested in the laboratories were taken out into the field and tested using different irrigation techniques. The pumps tested and irrigation methods can be seen in Table 6.
Table 6. The pumps and the irrigation techniques used for the field tests.
Zambian Suction Pump Furrow irriqation
Approtec Pressure Pump Furrow, hose pipe and sprinkler Swiss Suction Pump Demonstration purposes
Swazi Pressure Pump Hose pipe
KB Suction Pump. Furrow irrigation
The field tests took place in March 2001. They aimed to highlight design characteristics of the pumps that were not apparent from the laboratory testing phase. Pumps were tested under practical field situations for which they are likely to be used in the future. The pumps were not compared with one another but rather the applications of treadle pumps were tested in the field.
4.4.1 Boschkloof
The farmers' plot at Boschkloof irrigation scheme was surveyed using a dumpy level
and tape measure. Figure 17 shows the layout of the plot. The heights in metres are shown in
italics. The abstraction point at the canal is the reference height zero.
Distances are also shown.
26,gm
o It=::""I-~
FENCED AREA
~ •
;';O ~m :;:;;;:;;~ I 44'" ~\\\\\\\\\\\\\\
31 em
20 ROWS OF MAIZE SPACED
I m APART
2,!)f 2
'"
9275 m
Figure 17. The layout of the plot used for field testing at Boschkloof irrigation scheme.
The farmer had initially placed his Zambia S pump at position 1 marked in Figure 17.
An outlet pipe was attached to the pump and the water was flowing through this pipe to the furrows. This was used as the set up for the first trial. The Zambia S pump was then moved to the position marked 2 in Figure 17. The water then spilled directly from
the pump into a furrow. A similar set up as position 2 was then used for the last two trials, using the KB suction pump from India and the Approtec pressure pump from Kenya, without an outlet pipe. A class 6, 50 mm diameter pipe was used as the inlet pipe. The pipe was primed by filling it with water, before it was attached to the pump.
A non-return foot valve was placed on the end of the inlet pipe to prevent the water from leaking out when pumping stopped.
The farmer was asked to treadle in each set of tests. A stopwatch was used to record the time it took to fill a 25 litre bucket and the flow rate was then calculated. The water was then allowed to spill into the furrow being used. A tape measure was spread out along the length of the furrow.
The distance that the waterfront had reached after each minute was recorded.