Measuring Water flow:
Modern pumps make lifting water from one level to another an efficient simple process that can be measured with a high degree of precision using water meters.
An example of the ease with which this was accomplished was when employed by a mining company that decided to de-water an old mine that had been allowed to flood for more than 50 years.
Two 45cm x 25 stage centrifugal pumps were coupled to the end of 45cm steel pipes. These were slowly lowered down the main shaft each day with additional pipe lengths added, as the water level fell.
The streams of water from the two pumps were directed into a large earth drainage channel that led to a low lying area some miles away where it formed a large enough ‘lake’ to allow boating.
Contrast this with the ancient, somewhat inefficient methods, used to lift water from one level to another, such as the Shadoof, animal powered Sakia or Noria water wheel and the Archimedes Screw.
The shadoof was first developed in ancient Mesopotamia circa 2000 BC. It consists of an upright frame upon which is suspended a long pole or branch at approximately 1/5th of its length from one end. At the end of the longest section hangs a bucket or similar while at the shortest end the weight is attached.
When correctly balanced, the counterweight should support a half filled bucket of water so that some effort was needed to pull an empty bucket down to the water with the same amount of effort then needed to lift a full bucket.
Using an almost effortless swinging and lifting motion, the bucket is used to scoop up and transfer water from one body of water into runnels higher up that convey the water along irrigation channels in the desired direction.
Under ideal conditions, a shadoof is capable of lifting over 2500 litres per day from a maximum depth of 3 metres.
A Sakia, also known as a ‘Persian wheel’ is a water wheel used primarily in Egypt with the earliest being dated to the 2nd century BC. It consists of a large hollow wheel ranging in diameter from two to five meters with scoops or buckets at the periphery and is traditionally driven by draught animals.
Its unique characteristic is that water is dispensed near the hub rather than from the top thus reducing the amount of energy needed to lift the water.
A animal driven Sakia can lift water up from around 10 meters depth, and is thus considerably more efficient than a shadoof which can only lift water from around 3 meters.
Modern day Sakia’s are now driven by an engine and are able to make from 8 to 15 revolutions per minute as opposed to the 2 to 4 revolutions obtained from draught animals.
Greek engineers were responsible for inventing the undershot and overshot water wheel between the 3rd and 2nd century BC. These were further modified by the Romans around 300 AD who replaced the wooden compartments with ceramic pots attached to the outside of an open framed wheel thereby creating the Noria.
There are three types of Noria – the most common consists of a vertical wheel which is slung with a chain of buckets, the whole of which is driven by donkeys, mules or oxen.
Then there is the second type of Noria that uses the same system of a necklace of clay or wooden buckets but is instead driven by wind power.
The third form of Noria uses the energy of a flowing river to undershoot a very narrow waterwheel whose rim is made up of a series of containers which lift water from the same river up into a very small aqueduct at the top of the wheel.
Some Norias used in the medieval Islamic world were as large as 20 metres in diameter and could lift many thousands of litres per hour.
The Archimedes’ Screw is commonly attributed to Archimedes on the occasion of his visit to Egypt during the 3rd century BC.
It consists of a spiral screw inside a hollow pipe, with either the screw itself being rotated within the hollow pipe or the whole being rotated.
The Screw is positioned at an angle with the lower end in the water body from which the water is to be drawn. As the bottom end of the tube rotates, it scoops up some water which continues to slide up the spiral as it turns. Each rotation introduces another scoop of water which then follows up the spiral behind the water that is one rotation ahead, finally exiting at the end of the spiral, now some meters higher.
Besides being used to move water, this mechanism is also found in situations where a mixture of suspended solids and water needs to be moved from one level to another. Examples are lifting fish safely from ponds and then transporting them elsewhere.
This mechanism is also used to move granular material such as plastic pellets, grain in combine harvesters and even as compactors of waste material.
The above are, broadly speaking, water displacement devices in that they move / displace water from one position to another and thus by counting the number of ‘displacements’ in a given time cycle, multiplying this number by the volume of each displacement, a relatively accurate total volume of water moved would be determined.
Three of the devices, the Shadoof, Sakia and Archimedes Screw displace water with the aid of an external energy source, either human or animal, whereas the Noria does the work by utilizing the pressure of the flowing water into which it is immersed and so could be regarded as the forefather of the positive displacement water meter.