* The maximum lift is limited to about 12 m.
* The force needed to pump the water may be too great for children, especially if the water table is below 5 m.
====The VLOM concept====
The term VLOM (Village Level Operation and Maintenance) was coined during the World Bank / UNDP Rural Water Supply Handpumps Project which, from 1981 - 91, considered the availability around the world at that time of handpump technologies and maintenance systems.
A series of performance tests were undertaken involving laboratory testing of 40 types of handpump and field performance monitoring of 2700 handpumps.
It was concluded that centralised maintenance systems were the cause of many problems and that village level maintenance was desirable, but only feasible if the design of the pump made it possible.
Initially the VLOM concept was applied to the hardware, with the aim being to develop pumps which were designed to be:
* Easily maintained by a village caretaker, requiring minimal skills and few tools
* Manufactured in-country, primarily to ensure the availability of spare parts
* Robust and reliable under field conditions
* Cost effective
Subsequently, the VLOM concept was extended into software and organisational matters. Thus the "M" in "VLOM" has become "management of maintenance", for the success of a project was generally seen to be dependent on a strong emphasis on village management.
Therefore the following elements were added:
* Choice by the community of when to service pumps
* Choice by the community of who will service pumps
* Direct payment by the community to the caretakers
The application of VLOM principles, when considering pump selection, often involves compromising one principle to take advantage of another. A handpump with a low rate of breakdown might be thought preferable to another with a higher rate.
However, a handpump that breaks down monthly, but can be repaired in a few hours by a local caretaker, is preferable to one that breaks down once a year but requires a month for repairs to be completed and needs replacement parts to be imported and skilled technicians to be available.
The Afridev handpump was developed during the course of the project to embody all of the VLOM design principles. Production began in Kenya in 1985 and modifications were made after field trials in Kwale in Southern Kenya.
Improvements continue to be made. SKAT (Swiss Centre for Development Co-operation in Technology and Management) acts as a repository for the design drawings and specifications for the benefit of users and manufacturers of the handpumps.
==Costs==