|TREADLE PUMP FOR LOW LIFT IRRIGATION|
A treadle pump is a foot operated single acting double cylinder piston pump for low lift
irrigation. These pumps were originally developed in Bangladesh for pulling water up to the
pump level. Later they were adapted in Kenya to push water higher than the pump. The later
designs are referred to as "pressure pumps" because they can push water above the
Our latest treadle pump is manufactured for New Dawn Engineering by Appropriate Technology Exchange (Swaziland) (Pty) Ltd which trades as ATEX. It features 6mm thick cylinder walls and the latest patented valve design for treadle pumping. The ball bearing mounted steel pulley is retained. A wire rope option has been introduced ($3.00 extra) to replace the standard polypropylene rope. It is an efficient pump built to last and to survive being hauled around the African bush.
The main feature of the new valve is the proper sealing of the holes when the rubber flap is tightened into place. This means that a new pump with no water in it can suck and pump air without priming. This is an important advance in rural small holder irrigation. When a pump is used intermittently several problems arise, one of which is getting the air out of the suction line each time the pumping operation is re-started. The flap is a rectangle rather than a `D' shape so it is far easier to make a replacement in the field. The accuracy requirements are also easier to meet. The `D' is too difficult for most people to make and fit themselves. The rectangle can be easily made using only a bush knife. The flaps and the pump body are held together with wing nuts instead of bolts to almost eliminate the need for tools when doing routine maintenance. The development of the new valve plate and its incorporation into the base of a treadle pump rather than at the cylinder base represents a major step forward in bringing formal sector design standards to the "appropriate technology" market.
The maximum suction capacity of the pump is limited in practice to about 5 metres with 4 metres being a standard spec for mass produced pumps. New Dawn Engineering's newest design can produce just over 7 metres of suction (7.3 metres) however it has not yet been shown how much of this can be sustained in the field. In small quantities (under 100) the cost of the pump is E1000 (about $125).
At a "cadence" (frequency of pumping) of 50 strokes in 30 seconds a recent test by a 63 kilogramme operator showed an average output of 1.6 litres per second. The pump was placed on scaffolding 5.4 metres above a sump. This was a suction only test. There was no foot valve on the suction line. The test was conducted at 600 metres elevation so the effective lift (compensated for lower ambient air pressure) was 5.7 metres suction.
For any given operator weight there is a maximum suction+lift combination and that is related to the piston diameter. The pumps shown in the photos here all have 102mm diameter pistons. The layout of the pump limits the pressure a 70 kilogramme person to about 90% of body weight. This is because the piston is at the end of the treadle and the operator stands between the fulcrum and the piston. A 70 Kg operator can put about 63 Kg of force on the piston without having to pull upwards on the hand rest. In practice an operator can put far more than their own weight onto the piston because they can use the hand rest but there is a theoretical point being made here.
The 63 Kg of pressure on a 102mm piston can generate a maximum suction of 7.7 metres. Alternatively, if the water were level with the pump, the same operator could pump 7.7 metres vertically uphill. Any combination of these two also applies: 3 metres of suction and 4.7 metres of pumping up for a total of 7.7 metres.
This total lift may not suit all applications so the New Dawn Engineering treadle pump has an exchangeable cylinder set. The replacement cylinder set bolts onto the pump body without any modifications being required. If the pump is ordered with 76mm cylinders, the same operator can have a suction and pumping combination that totals 13.5 metres. There is "nothing for nothing" and the trade-off is that the output with smaller cylinders is reduced. Remember that to date there has been shown to be a practical limit on the suction side of 4 to 5 metres. A 2 metre suction with a 11.5 metre push is within the operational parameters of the treadle pump with a 70 Kg operator.
Another approach to this is to have two 40 Kg operators facing each other work the pump. The increases the available pressure on the pistons to 80 Kg. One operator has their weight discounted for standing between the fulcrum and the piston, and the other has their weight `bonused' because they are standing on the far side of the piston.
If a 50mm set of cylinders is fitted, the maximum suction+lift combination is 30 metres (100 feet). The output is proportionally reduced so with a 5 metre suction and a 25 metres push, you could expect to pump about 1800 litres per hour.
The treadle pump has fittings for a 50mm polyethylene suction pipe and can be fitted with either nitrile rubber (expensive) or leather seals. It also has a big footprint on the width to increase side-to-side stability using the inlet and outlet pipes as feet.
If you want to make some calculations yourself to see what you can get at different total head/operator mass combinations, use the following formula for a single operator:
Body mass in Kg times 0.07 divided by total head = sustainable output in Litres per second.
This formula does not tell you what cylinder diameter to use, only the likely sustainable output.
Click pictures to make larger.
Demonstration of the pump in action:
Pump body with shaped valve plates allows for proper sealing and simpler flap shape:
6mm thick 102mm diameter seamless cylinders fitted with 2 x leather seals each:
Pump body with exchangeable cylinders:
Two operators totalling 150 Kg operating a pump with 102mm cylinders:
Pump testing vacuum gauge:
The bottom is faced with rubber. It is pressed against the intake pipe hole while someone is operating the pump. -60 on the gauge would mean a 6 metre suction is created.