As discussed in previous posts, the most efficient way to transport water is by pumping it. There are a number of factors that come into play when pumping water and these will decide the right types and sizes of pumps to use. When designing a water transmission system, you need to always have the view from the system’s perspective as a whole. Once you have the requirements for the system, such as distance, head, evaporation, nearby power sources and of course how much water is needed at what pressure, only then can you design the system.
Pumps get more efficient the larger they are and the more pressure they need to supply. This is where a systems perspective is important. If you can combine all the pumping into as few units as possible, you can get a more efficient and more cost effective system. This isn’t always possible because sometimes farms are spread out along a river, for example, and it’s easier for the individual farms to take water from the river with their own pumps.
Hand pumps have been used for thousands of years. Buckets were used in the early days and then a few thousand years ago other pumps were developed, some are still in use. There is the Archimedes screw and rope pumps, but the most common over the past couple of centuries is the reciprocating pump. This uses a piston in a cylinder to pump water to the surface.
In the 19th century rotodynamic pumps were developed and these are smaller, more powerful and more efficient than the older positive displacement pumps. Virtually all large pumps used today are of this type.
These can be largely divided into two categories:
- Axial flow
- Radial flow (or centrifugal)
Axial flow pumps are great for large volumes at low pressures. Radial flow pumps are great for lower volumes and higher pressures. The other benefit of centrifugal pumps is that they can scale down for small scale irrigation. Most pumps used for irrigation are centrifugal types today. On windmills and historic pumps you will find reciprocating pumps.
Pumping water is only part of the system design. You also need to work out the water transmission, be it open cut channels or pipelines. You also need to work out the power source. The most common power sources are electric or diesel and in old farms you will also find wind powered pumps.
There are many variables at play and designing a water pumping and distribution system is a complicated task.