what is a rope pump?

“A rope pump system is a type of pump where a loose hanging rope is circulated down into a well and drawn back up through a long pipe with the bottom of the pipe immersed in water. On the rope, round disks or knots matching the diameter of the pipe are attached to the rope which pulls water to the surface.” – students’ Project Definition from their website

 

there are four main components to a rope pump:  the drive wheel, the rope, the guide box, and the riser pipe.  these can be seen in the schematic here.  the rope hangs in a loop, driven in a circle by the drive wheel and circulated through the water at the bottom of a well.  it’s threaded through a guide box at the bottom and a pipe on the way up.  knots or washer-type elements on the rope create a seal in the pipe and pull up slugs of water, pouring it out at the spout on top. 

this student team investigated multiple options for driving the rope, and a couple different concepts for the pump outlet.  since the pump is human-power driven, they looked at various ways of making the drive mechanism as efficient and low-effort as possible. In addition to the simple option of a hand-cranked wheel, they investigated various types of drives powered by bicycles.  this included those where the bicycle was removable and still usable and those where the bike is a permanent part of the pump.  both have pros and cons, of course, and the team used a decision matrix with their design criteria to come up with the best concept.  but there is nothing cheaper and easier than a simple mechanical hand crank made out of an old bicycle wheel.  in the end, they designed the system with such a hand crank and also designed an optional bike-driven add-on for those who could afford it (or build it from scrap materials).

for the base structure of the pump, they went with a modest a-frame construction, reducing the amount of material required overall.  the simplest outlet design is a single pipe , perpendicular to the rising pipe.  through experimentation, the team found there was wasted overflow at the top of the pipe and added a second outlet pipe which allowed full collection of the pumped water.  the frame was made from steel and all of the piping was PVC, both readily available and long-lasting.

rope with knots and seal

the suggested rope material is polypropylene, but polyester, metal cable or hemp rope would also work.  the key is that the rope must not absorb too much water (making it both heavier and more prone to bacterial growth) and must not stretch too much when wet or under tension.  while knots sized roughly to the inner diameter of the pipe work, the addition of simple washers and rubber (see picture) make the pump even more efficient and are relatively inexpensive to add.

guide box

the purpose of the guide box, at the bottom of the rope down in the well, is to redirect the rope from its way down back up through the riser pipe.  typically, a simple wheel in a box could accomplish this function, but that requires underwater installation.  this team’s solution is shown in the picture below:  a guide box made completely of PVC pipe.  the large pipe serves as a housing while the smaller pipes, which are flared, guide the rope into the box, give it an axle to turn around, and connect to the riser pipe as the rope goes up.  by attaching the riser pipe, this arrangement allows the guide box to be lowered into the well, without requiring special installation.

the design of this pump allows people to access aquifer water for safe drinking and efficient farming, at an amount they can reasonably save and invest.