Figure 1: Sakia - A water lifting device from Egypt Source: © Prof. Dr. Peter Wolff

Original title:

Scoop-wheels; Sakia; Tympanum or Tablia

Text and some figures by Fraenkel (1990). Other sources as indicated :

Fraenkel, P., 1990:

"The scoop-wheel (sakia in Egypt where it originated) has some factors in common with the noria. Although widely used in Egypt it has failed to become popular anywhere else. It is however an efficient and effective device." (Figure 1 and 2)

"It consists of a large hollow wheel with scoops around its periphery, which discharges water at or near its hub rather than from its top. The diameters for sakia range from about 2-5m; since water discharges at their hub level, the rule of thumb used in Egypt is that a sakia will lift water through a head of half its diameter less 0.7 m, to allow for the depth of submergence of the rim in order to scoop up water effectively. Therefore sakias of diameters from 2-5m will lift water from 0.3-1.8m respectively.

	Figure 2: Sakia or Tympanum (electrical powered in this case) Source: Fraenkel, 1990. (click to enlarge)

Sakias are now normally made from galvanized sheet steel. Second-hand vehicle roller bearings are commonly used to support the substantial weight of a sakia and its water contents. Most sakias are animal powered, but they are increasingly being driven by either mains electric motors or small engines, via suitable reduction gearing. The normal operating speed is 2-4 rpm for animal-driven sakias, and 8-15 rpm for motorised or engine- powered units.

Various different spiral shapes have evolved for the internal baffle plates in the sakia, and the Hydraulic Research and experimental Station (HRES) in Egypt tested various models to try to determine the optimum design. The best shaped designs " (Figure 3) " were measured as being as much as 50% better than the worst. Since some 300,000 sakias are in use in the Nile valley and Delta, optimization of the design could yield substantial aggregated benefits. An important feature of the three most successful sakia variants tested is that the outer compartments divided by the internal baffle plates discharge first into individual collection chambers which in turn discharge through holes surrounding the hub instead of having a common discharge orifice as on the more traditional designs. This prevents water running back into the compartment adjacent to it.

	Figure3: The Fathi is the optimum design of Sakia. Source: Fraenkel, 1990. (click to enlarge)

The types of sakia with separate discharge points for each compartment are distinguished by the generic name "tablia". A further advantage of the tablia type of device is that the water discharges a few centimeters above the centre shaft and therefore increases the useful head in relation to the diameter; especially with smaller machines. Typically a 3m tablia will lift water 1.5m compared with 0.90m for a centre-discharge sakia.

Another important conclusion from the tests by HRES was that for wheels operated in the 2-15rpm range, 6-8 compartments provide the optimum discharge. According to Molenaar" [1956] " , the following performance might be expected from traditional sakia designs:

Comparison of the above outputs those from a traditional persian wheel indicate that the sakia is somewhat more efficient, although of course it cannot lift water as high as is possible with a persian wheel."

(Click on figures to enlarge)

Figure 4: (left) A newly constructed sakia. The outer side of each spiral-shaped compartment bulges slightly outward near the intake end. This irregularity in shape increases the capacity of the device. Source: Molenaar, 1956 Figure 5: (middle) A typical sakia installation in the Nile Valley of Egypt. Source: Molenaar, 1956 Figure 6: (right) Close-up of the outlet of a sakia. Water discharges along the axle into a concrete trough from where it is led away to the place of use. Note that the axle rests on an unlubricated wood bearing. Source: Molenaar, 1956

The Figures 7 and 8 below show the characteristics for different categories of pumps and water lifting devices plotted on a log-log head-discharge graph giving the hydraulic power produced, which will be a lesser figure by the factor of the pump efficiency.

(Click on figures to enlarge)

Figure 7 and 8: Typical head and discharge capacities for different types of pumps and water lifting devices including "Mechanised Sakia and Flash Wheels" in Figure 7 (left) and "Sakia and Noria" in Figure 8 (right). Values are presented on a log-log scale (click to enlarge). Source (section): Fraenkel, 1990.