The BMS Purain Hydraulic Rainwater Jump Filter collects rainwater with optimal efficiency by imitating water flow in nature. 

This yields a filter that is highly efficient and has low maintenance requirements.  Options for fitting inside/outside of tanks are available.  A new Heavy Duty Version is now available, which can be fitted directly in the ground with no concrete surround.

As water flows over a drop, the water flow changes from a sub-critical to a super-critical flow as a result of the height drop. At the bottom of the drop water again returns to a sub-critical flow in a process known as hydraulic jump. This resulting increase in water power is similar to a strong eddy where impurities/debris are forced over the next level and washed away downstream.

Less is more

Unlike other self-cleaning filters the BMS Purain allows the filtration of light rainfall (up to 0.6mm in 5 minutes) with a collection efficiency of 100%. As 97% of annual rainfall is light rain, the overall efficency of the filter is 98%. Heavy rainfall of more than 0.6mm in 5 minutes, which happens 4 to 10 times per year, contributes approximately 3% of rainwater yield. The heavy rainfall causes a hydrualic jump within the filter, which is the optimal and natual way to rinse and clean filters.

Approved and fully tested

The BMS Purain has been successfully installed in more than 10,000 rainwater harvesting systems. To find out more about the ingenious filter and impressive test results from Siegen University’s Water Research Laboratory (Germany) contact BMS. The BMS Purain can be installed in any tank or system type and is a high specification excellent value product that is available for trade purchase in any quantity.

Special Features

  • Overall efficiency rate of 98%
  • Self cleaning and minimal maintenance costs
  • Very low height difference, complies with DIN 1986 and BS8515:2009
  • Purain 100 is supplied with an integrated overflow skimmer, non-return valve and small animal protection
  • The Purain 100 is installed in the Rainwater Harvesting tank. This means there is no need for installation in a seperate pit, saving both time and money.
  • Excellent Value.

Technical Description

  • Inlet (connecting sleeve): DN100
  • Outlet: DN100
  • Filter housing material: PP; 2.4 kg
  • Sealing material: EPDM/SBR
  • Valve/Filter material: VA
  • Filter gap size: 800 microns
  • Height Difference: 50 mm
  • Overall efficiency: 98%
  • Connectable discharge: up to 5.7 l/s

Stainless steel gap filter

The high quality, indestructible, stainless steel gap filter with a filter gap size of 0.8mm (800 micron), is an extremely reliable way of filtering dirt from rainwater. The smooth trapezoid filter gaps easily remove dirt and the resulting filtered water is perfect for use in washing machines, toilets and garden hoses or sprinklers. Use for body hygiene purposes is possible after further treatment of the rainwater by methods such as UV disinfection

Larger filters for inside and outside tanks

Purain Hydraulic jump filters for larger flows are available in DN150, DN200, DN300 and DN400 sizes. The larger filters work in exactly the same way as the Purain-100 filter. These filters can be installed directly in the tank for ease of installation if required.  The Heavy Duty (HD) filter is designed to be installed outside the tank.

The Purain HD Filter has a load capacity of up to 60 tonnes depending on ground conditions.  It can be installed directly in the ground without the need for a concrete surround or a seperate manhole and is the case with most other similar products and is very cost effective as it is made from high density polyethylene.  It is available in a variety of sizes and is easy and quick to install.  Please contact BMS and we will be happy to discuss your requirements.  A picture of Purain HD Jumpfilters from DN150-400 can be seen below.

Product Features

  • Overall efficiency rate of 98%

  • Self cleaning and minimal maintenance costs

  • Very low height difference, complies with DIN 1986 and BS8515:2009

  • Purain 100 is supplied with an integrated overflow skimmer, non-return valve and small animal protection

  • The Purain 100 is installed in the Rainwater Harvesting tank. This means there is no need for installation in a seperate pit, saving both time and money.

  • Excellent Value.

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