RM VLOM Bore and Well Handpumps

Assembly and Maintenance 

The Problems

The 2 most common hand pump designs found in developing countries, through varying design and materials properties, do not comply well with the VLOM (Village level operation and maintenance) principle. If they did we would not see the  very high rate of dysfunctional pumps in the field. 

One popular hand pump has a thin-walled PVC rising-main with glued section joints. This usually results in the rising-main being cut into manageable lengths during lifting for major maintenance. These then either have to be re-glued using special sockets, or replaced during re-assembly. Furthermore, the light walls commonly fracture during transport.  When installed in a large-diameter well, flexing of the thin walls results in fracture over time. Steel lift rods are usually of a standard 5 m length. These need to be cut to a critical length to match the pump cylinder depth - an operation that requires careful measurement and is often miss-calculated by semi-experienced technicians. 

Another common  heavy duty hand pump has a steel rising main. These and the lift rods need to be cut and threaded when desired inlet depth does not match the standard section lengths. This requires expensive threading tools and heavy lifting chain blocks, which is way beyond what a VLMO design requires. In the field the threading equipment inevitably ends up damaged and useless. Its use requires trade engineering training. 

How does the RM Hand Pump design address these potential problems? 

The rising-main: Sections are BSPT threaded heavy-walled PVC pipe manufactured to strict US standards. The standard lengths are 2 m with shorter sections down to 250 mm included in each kit. This eliminates any cutting and threading. This pipe is rigid enough to install in large-diameter hand-dug wells without lateral support. It can be installed in boreholes from 100 mm diameter upwards. 

The lift webbing: Adjustment of the webbing is via one stainless steel clamp of a design used in yacht rigging. It can be easily adjusted by hand and is intuitive to even the least mechanical member of a community. The very long potential stroke location (due to a 700 mm long cylinder) means that the webbing length (piston location in the cylinder) can vary by as much as 400 mm without effecting performance. For security reasons access to the web adjuster is via the top cover, requiring removal of 4 bolts. Excess webbing is provided in each kit. It is simply cut to the desired length -  leaving some overlap beyond the clamp. 

To be continued