The PURAIN Rainwater filter, also known as the hydraulic jump filter, is the innovation for roof areas typically found in single family dwellings.

This hydraulic jump technology cleans itself automatically. The design model for PURAIN Rainwater filters comes from nature: At almost every course in a stream, you can see how the hydraulic jump functions. The water flows over one of the stones, smooth and rounded by the action of the water over time. The water flow is substantially changed by the height drop, from a sub-critical to a super- critical flow. At the bottom of the dip, the waterflow changes again to a subcritical flow in a process now commonly known as hydraulic jump. This resulting increase in water power is similar to a strong eddy and any impurities are then forced over the next level and washed away downstream. Finally a filter that is low maintenance and self-cleaning!

Documentation:
Brochure

Purain DN 150-S Spec Sheet

ACCESSORIES

6" pipe connection kit

Backflushing nozzle

Calming inlet

Low rainfalls

Low rain­fall events ac­count for over 97 % of total an­nual rain­fall. There­fore, it is par­tic­u­larly im­por­tant that the fil­ter be de­signed to col­lect this light rain­fall. While many fil­ters are not de­signed to col­lect light falls, the rain­wa­ter col­lected in the hy­draulic jump fil­ter tray is then fil­tered and drained into the tank. The tray en­sures that no pre­cious water is lost.

High Rainfalls

High rain­fall events, that occur ap­prox. 4 to 10 times in a year, con­tribute only about 3% to total water yield and are used by the PU­RAIN Rain­wa­ter fil­ter for self-clean­ing. These high rain­falls lead to the for­ma­tion of an eddy in the PU­RAIN rain­wa­ter fil­ter, the so called hy­draulic jump, which spins with such great force that even dirt ac­cu­mu­lated in the tray is flushed and dis­charged with the over­flow.

The PU­RAIN Rain­wa­ter fil­ter cleans it­self dur­ing heavy rain­fall events. It means min­i­mum main­te­nance costs for the user in com­par­i­son to other fil­ter sys­tems.  An over­all rain­wa­ter fil­ter­ing ef­fi­ciency of 98 % is achieved with the unique, self-clean­ing PU­RAIN Rain­wa­ter fil­ter.  
With the hy­draulic jump fil­ter, this water is col­lected in a tray, which is then fil­tered and drained into the tank. The tray en­sures that no pre­cious water is lost. 7.7 lbs of sand-gravel mix­ture was flushed away in just 30 sec­onds dur­ing this trial (see photo) due to the ef­fi­ciency of the hy­draulic jump.

PURAIN 150 in a commercial application 

Where can I in­stall the PU­RAIN rain­wa­ter fil­ter?

The IN­TEWA PU­RAIN fil­ters can be eas­ily in­stalled in most stan­dard tanks of  plas­tic, con­crete, in­door and out­door con­struc­tion. Many dis­trib­u­tors de­liver your stor­age tank al­ready fit­ted with a PU­RAIN fil­ter. The PU­RAIN Fil­ter is also suit­able for in­stal­la­tion out­side the tank if re­quired. HD Fil­ters are de­signed for di­rect sub­sur­face in­stal­la­tion. While in­stalling the PU­RAIN fil­ter, make sure that a lower height off­set is pre­sent be­tween the in­flow and the out­flow.

Is there a fil­ter with­out height off­set be­tween in­flow and out­flow?

The PU­RAIN rain­wa­ter fil­ter works with the min­i­mum pos­si­ble height off­set be­tween the in­flow and out­flow. A height off­set is a pre­req­ui­site for a self-clean­ing fil­ter in order to en­sure proper op­er­a­tion. Since 1993, IN­TEWA has ac­cu­mu­lated a lot of ex­pe­ri­ence test­ing dif­fer­ent types of self-clean­ing fil­ters – none of which, func­tion with a high de­gree of ef­fi­ciency. Al­ter­na­tively, only a col­lec­tion fil­ter may be used in place of a hy­draulic jump, how­ever they have to be cleaned reg­u­larly and do not guar­an­tee the best qual­ity water fil­ter­ing.  

Is the rain­wa­ter fil­tered by PU­RAIN well suited for wash­ing ma­chines?

The water fil­tered by the hy­draulic jump fil­ter is per­fectly suited for use in toi­lets, wash­ing ma­chines etc. It should be noted that the qual­ity of water also de­pends on the stor­age of the rain­wa­ter. Fac­tors, such as tem­per­a­ture of the stor­age tank, in­flow calmer, over­flow skim­mer,  size of tank, etc. are crit­i­cal for an op­ti­mum qual­ity of water.

Does self clean­ing = main­te­nance free?

The PU­RAIN-fil­ter is ex­tremely low main­te­nance. Dirt and leaves in the sed­i­men­ta­tion cham­ber do not need to be re­moved be­cause they will be flushed away with the next heavy rain­fall. If the sieve does be­come clogged, it is eas­ily cleaned through the tank lid with a high pres­sure cleaner. Al­ter­na­tively, in rare cases, the sieve can be re­moved for clean­ing. Should a fil­ter be mounted in a hard to ac­cess place, it can also be cleaned via the in­stal­la­tion  of a back­flush­ing noz­zle. This is avail­able as a PU­RAIN ac­ces­sory. We rec­om­mend that you check your fil­ter about sieve twice a year.

How is the ef­fi­ciency in other con­di­tions of rain?

The over­all ef­fi­ciency of the PU­RAIN rain water fil­ter is rated at 98 %. Hereby, the small to medium rain­falls are col­lected 100 %, but the heavy rains (which ac­count for only about 3 % of an­nual rain­fall yield), are uti­lized for the self-clean­ing func­tion of the hy­draulic jump fil­ter. Even in areas which ex­pe­ri­ence more heavy rain­falls the ef­fi­ciency of the PU­RAIN fil­ter is well over 95 %.

How do I in­stall the non-re­turn valve and over­flow skim­mer used with the big­ger PU­RAIN rain­wa­ter fil­ters?

The non-re­turn valve and over­flow skim­mer, made from moulded parts, are sep­a­rately in­stalled in the tank.