UNDERGROUND STORAGE TANK

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Underground Storage Tanks

When buried or underground storage tanks are used for the storage and reception of water for domestic purposes, the following requirements shall be complied with:

·         The top of the tank shall ‘be so leveled as to prevent accumulation of water thereon

·         The .tank. shall ‘have a complete cement concrete cover leaving a manhole opening provided with a properly fitting mosquito-proof hinged cast iron cover fitted with a leak proof cast iron frame. Where tank is of a large size, adequate number of manholes shall be provided.

·         No gap shall be allowed to remain round the suction pipe and arrangement shall be provided for proper discharge, of spill water from the electric pump by connecting the pump cabin to the water drain, or by providing a small hole which will enable the water to flow out.

·         The overflow pipes or vent shafts, if provided, shall have a wire gauge cover of 1.5 mm mesh properly screwed tightly to the opening.

Jointing of Pipes to Storage Tanks

For jointing steel pipe to a storage tank, the end of the pipe shall be threaded, passed through a hole in the tank and secured by back nuts both inside and outside. The pipe end shall be flush with the face of the inside back nut to obviate corrosion of the pipe threads. For joining copper pipe to steel or copper tank a connector of non-ferrous metal shall be used having a shoulder to bear on the outside of the tank and secured by a backnut inside.

Storage Capacities

The quantity of water to be stored shall be calculated taking into account the following factors:

·         Hours of supply at sufficiently high pressure to fill up the overhead storage tanks

·         Frequency of replenishment of overhead tanks, during the 24 hours;

·         Rate and regularity of supply

The particulars of water supply requirements of residential buildings and of buildings other than residences are given under 3.1 and 3.2 of IS: 1172-1983*. It has been stipulated that, where there is full flushing system a minimum of 200 liters per head per day shall be assured out of which about 45 liters per head per day may be taken as flushing requirements and the remaining 155 liters for other domestic purposes.

Pumping of Water

In case of multi-storey buildings where the height of the fitting or storage tank is such as will not permit of their being fed with the available pressures in the water main, pumping is necessary.

The house service pumps are usually of the centrifugal type driven by electric motors, where electric power is available.

In cases where pumping is necessary, storage tank shall be provided either at the ground level or partially buried underground, in which case it shall conform to the requirements given under 11.9 for underground storage tanks.

The storage tank should have a minimum capacity of 50 percent of the overhead storage tank.

The advantage of the storage tank is that it can be fed continuously during low pressure hours and, therefore, the pump can be worked at any time of the day and the overhead storage ‘may be replenished continuously.

The pump also works at a steady head and there is no chance of overloading.