Saturday was an easier day – we stayed in town at Gulu University where there was still a well to repair. We also ran a 2D resistivity line to compare to 1D resistivity surveys students had run at the university in past years.
The well at the university was particularly interesting because it used a rope pump, not the usual India Mk 2 we see at other sites. A few notes on how these work:
- Both these wells have approximately 5 inch casing put in when the well is drilled. Part of this is screened so water can enter from the formation. Inside the well is a much smaller (1-2 inch) riser pipe that the water comes up. Different pumps lift the water in different ways.
- India Mk 2 pumps have housing at the bottom of the well with two one-way valves. These are connected to the handle at the surface by a long metal rod that is inside the riser pipe. When you lift the handle, the top valve opens and moves down the water column a little. When you push the handle down, this valve closes, and the bottom valve opens, pulling more water into the housing. Repeated pumping slowly pulls up a column of water.
- Rope pumps are a bit more primitive. Basically you have a rope that is looped up through the riser pipe, over a wheel at the surface, then back down the well outside the riser pipe. This rope has little rubber disks (punched out of tire) that are the same diameter as the riser pipe. Spinning a handle on the wheel at the surface pulls the rope up the well, and each disk carries some water with it.
- These pumps have advantages and disadvantages – rope pump is cheaper (equivalent to ~USD$100 , whereas the India Mk 2 is ~USD$500-700). Also, rope pump can potentially bring more water up if you spin the handle faster. However, rope pumps take much more effort to pump and are somewhat harder to maintain.
Anyway, it was very educational seeing this pump fixed, and also nice to have another working pump at the university.