As the name implies, the automatic valveless gravity filter operates automatically, on the loss of head principle. This is usually accepted as being the most accurate control besides the constant analysis of the filtered water turbidity that is rarely practical on a consistent basis. The head loss at which the auto valveless gravity filter initiates backwashing is ascertained by the height of the inverted U-turn at the top of the backwash pipe. The water level in this pipe is proportional to the head loss across the filter bed.
In a typical filtering operation, water gets filtered while traveling across the sand bed. The suspended solids gets collected in the filter bed during normal functioning, and differential pressure start increasing that causes the level of water to rise in the backwash pipe. When the level of water reaches the top of the loop, siphon action begins and the backwash starts. The wash water flows from the storage compartment through the sand bed, and is discharged through the back wash pipe. The siphon breaker terminates the wash cycle.
Design
The auto valveless gravity filter comprises of a tank divided into 3 functional compartments - a backwash storage space, a filter bed compartment and a collection chamber under a false bottom. The backwash storage space is constructed to hold the sufficient amount of backwash water. The filter bed compartment generally contains standard fine filter sand supported on a collection system of disc type plastic strainers that facilitate uniform collection of filtered water and uniform distribution of backwash water without using gravel. Standard filter sand or dual media (anthracite and sand) is normally used as the filter media. The filter can be built in cylindrical steel or rectangular concrete construction.
Some of the salient features of modern day auto valveless gravity filter include -
- Automatic backwash, hence reliable
- Minimum maintenance required, as there are no moving parts
- Easy to install and operate
- Uniform high quality treated water
- Compact and modular design, hence low expansion and installation cost
Some of the important applications of an auto valveless gravity filter include -
- Raw water clarification
- Ideal for side stream filtration of cooling towers, i.e. Primarily for low turbidity applications
- Treatment of potable water
- Polishing filter for domestic sewage as well as industrial effluent