Migration

Part 9 - Water Pumps

We can live without food for about three weeks but only three or four days without water which must have greatly worried our remote ancestors on the dry African savanna. The atmosphere endlessly recycles water by evaporation and then deposits the water in the form of rain or snow. But it is often erratic and, when streams and rivers run dry and pools of water dry up, unavailable. Most animals will dig in the softest part of a dried up water hole and our ancestor probably dug much deeper to reach water but most human settlements were near rivers and lakes that seldom disappeared. Rain is almost pure water when it falls but it rapidly dissolves minerals and organic material so most surface run off, from rivers, lakes, streams and muddy waterholes, is polluted with bacteria, viruses and fungi some of which can be harmful. Water which has filtered deep underground has usually been there long enough to become free of live organisms and is inherently safer to drink. In times of droughts, hunter gatherers were forced to move in search of water but as they became farmers they had to find ways to find and conserve more water for their plants and livestock. 

As the population grew, people had to move farther away from the best land near water. Along the river Nile, farmers dug canals and ditches so that water would flow to their crops or relied on seasonal flooding. They often dug deep under ground to reach water, finding this well water to be more pure for drinking than surface water but then, faced with tedious work of hauling water to the surface in buckets around 2000 BC, Egyptians invented the shaduf; the first lift pump. It used a long suspended beam with a bucket at one end and a counterweight at the other. So, instead of lifting the bucket, the worker pulled the bucket down and allowed the counterweight to lift the water filled bucket.

Lift pumps

About 200 BCE Archimedes designed the screw pump, one of the greatest inventions of all time and still in use today all over the world.

Chain pumps appeared in Babylon and Egypt in the first millennium BCE. They typically used a continuous loop of rope or chain with small buckets placed at intervals along its length. A later version used disc of rag or leather pulled up through a tube. With the bottom of the tube in water, the chain or rope was pulled up the tube by hand, or with a winch. The water, trapped between the discs, was lifted up and discharged at the top. Chain pumps were used to prevent mines from flooding and on ships to pump water from the bilges. 

The Chinese invented a chain lift pump by attaching squares of wood along a continuous chain of wooden links driven by people stepping on bicycle-like pedals. The squares fitted neatly into a three sided trough one end of which was in the water and the other at field level.

Suction pumps.  The typical village pump) used a piston in a cylinder to lift water from a well. As it relied on atmospheric pressure, it worked only when the water level was less than about 7 metres (23 feet) below the pump but this was not understood until much later. A siphon (or syphon) was used in Roman times to lift water over an obstacle. It was simply a rigid tube with one end in the water to be moved and the other end lower than the level of water. The tube was temporarily blocked at both ends and the tube filled with water. When both ends were opened, the weight of water falling out of the exit end sucked water into the entry end continuously. This worked as long as no air got into the tube to break the partial vacuum at the top of the tube.

Force Pumps

The first force pumps were almost identical to the suction pumps. They were piston and cylinder types familiar as the medical syringe but they were placed under water and the water forced up under pressure.

They were capable of propelling water with considerable force and were first used for decorative fountains and then later on pumping engines used to fight fires in Rome. (The French word for fire-fighter is pompier (pumper). Water is first sucked into the cylinder as the piston is raised. It is then expelled through a valve as the piston is forced down. The other side of the cylinder may also be used so that the water is sucked in and expelled with each stroke of the piston. The pressure of water depends only on the force applied to the piston.