Tank Capacities |
Tank Terminology:
| Effective Capacity is the volume of water that is available for use |  |
| Nominal Capacity is the total capacity of the tank. |
• Loss (Top) is the distance betwen the top water level and the top of the tank
• Loss (bottom) is the distance between the bottom water level and the bottom of the tank.
Basic Calculations:
It is the customer's responsibility to provide the required draw-off, capacity needed and required water pressure for each application.
Nominal Capacity in Kilolitres = the radius of the tank2 x 3.142 x tank height (all in metres)
The Effective Capacity in Kilolitres may be calculated by using the same formula, but having firstly subtracted loss at top + loss at bottom from tank height.
Calculation of Required Storage:
There are two methods of storing water - firstly, ground level mounted tanks where water is drawn off via pumping systems and, secondly, high level storage tanks which provide gravity feed at pressure for reticulation.
At ground level, if the water being stored does not need to be supplied at a specific minimum pressure (the volume of water available is the only consideration), then required storage capacity (in Kilolitres) may be calculated by using the basic calculations given above. However, if the draw-off is greater than the supply, then water must be kept in storage to allow for peak usage. This required storage is calculated by using formula (a):
(a) Required storage = (water draw-off rate Lt/Hr- flow rate into tank Lt/Hr) x hours of usage at draw-off rate
If, for ground level tanks, the water leaving the tank needs to be at a specific minimum pressure, the minimum volume which must remain in the tank to maintain the desired pressure is calculated using formula (b):
(b) Minimum volume in tank Kl= (pressure required in metres head + bottom loss in metres) x (radius of tank 2 in metres x 3.142)
The additional storage required to maintain this volume at all times is calculated by using formula (a). Therefore the overall required storage for water at a specific minimum pressure is (a) + (b).
Elevated tanks are used for pressurised reticulation. Tanks should be mounted on tankstands or at a higher location. Southern Cross tankstands are available for elevated water storage and boosted pressure. Special decking material is required to support the liner.
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