Water distribution system of stainless steel manganese sand filter is one of themain elements ensuring stable operation of the equipment. Its function is to evenlydistribute the raw water to be treated over the entire cross-section of the filter tank,avoid the phenomenon of localised concentration of water flow (displacement),ensure full contact between the raw water and manganese sand filter media, and atthe same time evenly distribute the backwash water flow in the backwashing stageto fully agitate and thoroughly clean the filter media layer. The detailedclassifications, structural features and design considerations are as follows:
I. Common Types and Structures of Water Distribution Systems
1. Inlet end of top water distribution system
(1) Water distributor of branch pipe type (water distribution of main branch pipe)
Structure : It has one main pipe with some branch pipes that are radiallydistributed. The branch pipes are evenly equipped with water distribution holes (orwater distribution nozzles) The main pipe connects to the water inlet. The main pipesupplies raw water to each branch pipe and evenly distributes it to the filter medialayer through the water distribution holes / nozzles.
Material: Same as the tank body, stainless steel (304/316). The diameter of waterdistribution holes is usually 3-5mm. The hole spacing is designed according to thediameter of the tank body (generally 100-200mm). The opening direction is mostlydownward or 45° downward to avoid direct impact on filter media and loss.
Suitable for: Medium and large stainless steel manganese sand filters (tankdiameter > 1.2m), with good water distribution uniformity, strong anti-cloggingability.
(2) Water distributor of baffle type
Structure : Under the water inlet, a structure shall be provided.
Features: Simple structure and low cost, suitable for small filters (tank diameter<1m); but the water distribution uniformity is poor, and the water flow is fast at theedges and slow in the centre. Long term usage can cause local caking of the filtermedia layer.
(3) Screen type water distributor
Material: Structure of stainless steel
Additional function : It also acts as a pretreatment to intercept large suspendedsolids, so that large impurities do not enter the filter media layer and causeblockage. The screen needs to be cleaned regularly to avoid blockage and affecting water distribution efficiency.
2. Bottom water distribution/collection system (filter outlet + backwash inlet)
The bottom water distribution system of the manganese sand filter has twofunctions, "backwash inlet water distribution" and "filtered water collection", andneed to meet the requirements of uniform water distribution and no loss of filtermedia.
(1) Water distributor type (filter cap)
Structure : It is composed of a perforated plate (or a reinforced concrete supportplate) and a large number of filter caps. The gap width of the filter caps is smallerthan the minimum particle size of the manganese sand filter media (usually 0.2-0.3mm). The filter caps are evenly installed on the perforated plate.
Working principle: In the filtration process, clean water enters the water collectionchamber through the gaps in the filter cap and then flows out; in the backwashingprocess, backwash water is uniformly sprayed from the water collection chamberthrough the filter cap, disturbing the manganese sand filter media layer.
Advantages: Good uniformity in water distribution/collection and good filter mediaretention effect, being the most widely used type nowadays; Disadvantages: Highinstallation density (100-150 units/m2), requiring secure installation to prevent filtercaps falling off and filter media loss.
(2) Johnson tube, wire-wound tube water distributor
Structure : It is composed of several parallel winding tubes, the gap width (0.2-0.5mm) of which is precisely controlled, and the tube body is fixed on the bottomsupport.
Features : High pressure resistance and anti-clogging, applicable to manganesesand filters under high pressure conditions, but the water distribution uniformity isslightly inferior to the filter cap type and the cost is higher, so it is mostly used inlarge industrial equipment.
II. Major Design Requirements
Uniformity of water distribution The openings / slits of the water distributionsystem shall be evenly distributed so that the velocity deviation of the water flowingthrough the filter media layer shall be <10%, and avoid excessive wear or caking oflocal filter media.
To avoid loss of filter media: gaps/pore sizes of components of water distributionshould be less than the minimum particle size of manganese sand filter media(common particle size of manganese sand is 0.5-1.2mm, so the gaps should be ≤0.3mm).
Corrosion resistance, pressure resistance: The stainless steel material should becompatible with the water quality to be treated (for example, 316 stainless steelshould be used for chlorinated water). The pressure resistance of the waterdistributor should be greater than or equal to the working pressure of the filter(usually 0.6-1.0 MPa).
Backwash compatibility The water distribution system should be able to meet therequirements of backwash water flow rate (for manganese sand filters, thebackwash flow rate is generally 10-15 m/h), so that the filter media layer can fullyexpand during backwash (expansion rate 30%-50%) and wash out the iron andmanganese oxide impurities retained.
III. Maintenance and Common Failures
Uneven water distribution Typically due to clogged water distribution holes ordetached filter caps; Water distribution parts should be periodically removed andcleaned. Broken filter caps/nozzles should be replaced.
Filter media loss : Look for if the gaps of the water distribution are too large or thecomponents are loose . Replace any uncertified water distribution componentsimmediately and replenish any lost manganese sand filter media.
Corrosion damage: If the water contains corrosive media (such as strongacid/alkali), you need to replace with a higher grade stainless steel (such as 316L) orapply anti-corrosion coating.
