output pvc pipe inside the filter container?

  • H2Oguy


    Does anyone have experience testing or operating a biosand (slow sand) filter with the pvc output pipe running up inside the container – surrounded by the filter sand instead of outside the filter container? We have been studying, building and testing biological sand filters here for two years using roof water and surface water with much success; however the winters are cold and the output pipes have frozen up several times requiring complete removal of all the contents to repair the cracked pipe. Two websites with all the info and test results we have so far are:
    Thank you for any suggestions.

  • Eric


    Hi Dave

    We used to put the pipe internally when making filters in Sudan. Just use PVC drainage pipe, maybe 15-20mm diameter. A horizontal section can lie on the filter base inside – this can be perforated o on the underside. This then bends upwards and follows the filter wall inside until it bends again and exits the filter wall.

    The bends can be made using PVC fittings in your case. The place where it exits the wall needs to be kept watertight – I think you will have best success by using a male and female threaded PVC adaptor on either side. The adaptor piece has a threaded side and a smooth side. The male thread component of one of the pieces goes through the hole in the wall and screws into the female thread component. Then both of them are glued to PVC pipes to continue. To make it watertight, 2 washers made of car or tractor inner tube should be cut and put on either side of the filter wall – when you tighten the adaptors together they will press on these washers.

    Hope this helps.


  • Guest


    Q1. This was just the question I was going to ask, We plan to build 2, possibly 3, practice BioSandFilters in plastic barrels /containers before leaving the UK and going abroad, – is possible/ok to put the up outlet pipe INSIDE the barrel /container? as we think it less likely to get broken off or damaged and there will be less water-pressure on the hole if is at the top than at the bottom of the barrel, so less likely to leak.

    Q2. Is it ok to use ordinary every day Garden Hose? as this is easily available, easy to cut (garden secateurs) and the attachments are easy to use (just click them together).

    Q3. Are the 2 gravel levels at the bottom simply to keep sand out of the finished water and not clog the outlet pipe up or are they part of the filtration process? Would a second diffuser plate do the job just as well?

  • Guest


    …also further advantages to using ordinary everyday hose is; it is flexible, if you knock it hard, it will just bend not break off, it will not need special attachments like T- junctions and L-bows or stoppers or accurate cutting or any special glue, unlike PVC tubing , if you have made the drain array slight too big for example, just spiral the hose a bit more you don’t have to be too careful with it, get all your measurements super accurate.

    To make to the “Drain Aray” as I said we were planning to just use some hose spiralled at the bottom of the barrel with some nail-size holes banged into it, with the holes facing upwards we also plan to use hose to make the baffle, again with hose with some small holes banged into it facing upwards possibly inwards towards the side of the plastic barrel so the water just trickles down. Is this a sensible idea in your experience or have we missed something big?

    Oh, by the way, I forget to put my name last time, it is Carl. I look forward to your reply, many thanks for your help. Carl :o)

  • Eric


    Some answers:
    Q1 – yes perfectly possible. See the ‘Sand filter types’ part of the website where you can see what we did for plastic filters.
    Q2 – it’s fine I guess. Just so long as the place where the pipe exits the barrel is watertight. Normally with rigid pipe, this is done using male- and female-threaded adaptors with rubber seals, so not sure how that works exactly with flexi hose but I’m sure there is a way. Hose should also be wide enough so that there is no siphon effect (i.e. water stops when water level reaches where hose exits container) – in my experience, 5mm hose siphons whereas 20mm hose does not.
    Q3 – function is partly to stop pipe clogging, but more to increase water velocity as it exits the sand, otherwise water flows too slowly. Similar principle to why borehole drillers put coarser material around the intake screen, so as to increase flow rates into the borehole.

    Would put holes on underside of hose myself just to reduce any clogging in case.

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H2Oguyoutput pvc pipe inside the filter container?