Difference between revisions of "Deep-well piston handpump"

Revision as of 00:12, 18 October 2012

Afridev pump: a deep-well piston handpump.
Photo: S.K. Industries.

With a deep-well piston handpump, the piston is placed in a cylinder below the water level, which is usually 15–45 m below the ground. The pumping motion by the user at the pump stand is transferred to the piston by a series of connected pumping rods inside the rising main. On the up-stroke, the plunger lifts water into the rising main, and replacement water is drawn into the cylinder through a foot valve. On the down-stroke, the foot valve closes, and water passes the plunger and is lifted on the next up-stroke. The pumping height is limited only by the effort needed to lift the water to the surface. Nowadays, most pump cylinders have an open top. This allows the piston and foot valve to be removed through the rising main for servicing and repairs, while the rising main and cylinder stay in place. The pump rods have special connectors that allow them to be assembled or dismantled without tools, or with only very simple ones. The connecting joints incorporate pump rod centralizers that prevent wear of the rising main. To a large extent, improved models can be maintained at village level.

Suitable conditions

Range of depth: 15–45 m, although depths of up to 100 m are possible.

Useful life: 6–12 years.

Yield: 0.25–0.36 litres/s at 25 m, and 0.18–0.28 litres/s at 45 m depth.

Area of use: Rural and low-income periurban areas where groundwater tables are within 100 m (but preferably within 45 m) from the surface.

Construction, operations and maintenance

The pump is operated by moving the handle up and down, or by rotating the handle of a flywheel. This can be done by adults and even children, since handle forces are usually kept within acceptable limits (depending on the brand and lifting heights). Preventive maintenance usually consists of checking that the pump is functioning, and cleaning the pump and pump site daily. Each week, the pump should be greased, and once a month all parts of the pumpstand must be checked. Small repairs include replacing bearings, cupseals and washers, and straightening bent pumping rods, etc.

Once a year, the entire pump should be dismantled for a check, the parts cleaned with clean water, and the pumpstand painted. Pump rods that show bad corrosion must be replaced. Under normal conditions, a galvanized steel pump rod needs to be replaced every five or six years. Rising mains made of galvanized iron should be removed and checked, and pipes with badly corroded threads replaced. Major repairs involve replacing the plunger, foot valve, cylinder, pump rods, rising main, pump handle, fulcrum, etc.

With open-top cylinder pumps, all preventive maintenance activities can normally be carried out by the pump caretaker for the village. With closed-top cylinder pumps, however, special lifting equipment may be needed to pull up the rising main and cylinder, so that pump parts down in the well hole can be maintained. Deep-well pumps can be too expensive for individual families, and they may be better suited to communal use. To maintain the pump in good working condition, communities will have to organize themselves, for example, by appointing a pump caretaker, or by coordinating activities through a pump committee. External support is often provided by state or nongovernmental organizations, but this can be costly. In some cases, small private enterprises, paid directly by the communities, are now doing this job satisfactorily.

Potential problems
— the most common repair is replacing the plunger seals;
— there can be problems with the quality control of local manufacturers, especially in African countries;
— the hook-and-eye connectors of the pump rods tend to break more often than conventional connections, and the rods may also become disconnected, or bend spontaneously;
— corrosion is a problem, especially where the groundwater is aggressive, and it can affect the pump rods if they are not made of stainless steel, the rising main (if not galvanized iron tubing), the cylinder, the housing for the pumphead bearing, and other pumpstand parts;
— handles become shaky or broken, mainly because of worn-out bearings;
— the number of problems usually increases with increasing depth of the groundwater (the maximum lift for a pump varies according to the brand, but is usually 45–100 m).
— with some pump brands, or when the water must be lifted from a great depth, the pump handle may require considerable strength to turn it;
— to reduce the number of major repairs, the rising main should be made of the highest-quality material available;
— rigorous quality control is needed for deep-well piston handpumps, since many are produced in developing countries;
— deep-well piston handpumps may require considerable torque to start them, and the pump may be driven by a windmill; as a result, rotary pumps are often preferred because of their lower starting torque.

Costs

In 1985, for a well 25–35 m deep, prices ranged from about US$ 40 for a cylinder, plunger and foot valve set (installed under a locally-made pump head), to over US$ 2300 for a complete pump with stainless steel parts. Most good pumps cost US$ 300–500.

Acknowledgements

• Brikke, François, and Bredero, Maarten. Linking technology choice with operation and maintenance in the context of community water supply and sanitation: A reference document for planners and project staff. World Health Organization and IRC Water and Sanitation Centre. Geneva, Switzerland 2003.