Water Hammer - Arrestor - Banging pipes SUCCESS

Discussion in 'Plumbers' Talk' started by r18rws, Sep 18, 2017.

  1. r18rws

    r18rws Member

    Had asked on here a few times and got mixed feedback, so this is more a bit of info for anyone else who comes along with the same problem.

    For me it was a banging pipe in ceiling/floor between ground and first floor. Didn't want to take the ceiling down, nor the tiled floor up but every time any toilet flushed in the house there was a massive thud as the fluidmaster inlet closed.

    Bit the bullet and bought a shock arrestor from screwfix and installed it (along with a female tee and a flexible hose with valve), and that loo stopped the banging.
    Checked the other two toilets but still made the pipe bang so did the same on the other two loos in the house, (although nowhere near the pipe that banged they must have still been on that pipe run as the noise persisted) and I guess there was clip missing or something.

    Good news, they worked and at £26 for all the bits for each loo, I am well chuffed. There was a smaller version but not in stock locally, probably the same thing but this seemed more substantial and was adjustable for the pressure to some extent.

    It may have been cheaper to take the roof down and fix it properly, but beyond my skills, and knowing my luck I would have fixed the pipe in one place and the issue would have moved along to another bit!

    IMG_1134[1].JPG

    http://www.screwfix.com/p/reflex-ex...gclsrc=aw.ds&dclid=CPeZm8XzrtYCFaKM7QodLV8O5A
     
  2. Des Lavender

    Des Lavender Member

    Let's hope this does the trick for my bathroom cistern. Now only £24.48!! Collecting tomorrow.
     
  3. rogerk101

    rogerk101 Screwfix Select

    I had the same problem in a house, with toilets shut-offs closing fast, but also with quarter turn taps shutting off water flow far faster than their multi-turn counterparts.
    Rather than installing a shock arrestor for each device, I just installed a big one (about 10 litres) at the highest point in the water system. It solved it for the whole house.
     
    Heat likes this.
  4. Heat

    Heat Screwfix Select

    Those shock arrestors have an air charge in them I think (and will require it recharged occasionally) - as are basically just little expansion vessels, so I would have just tried a single large potable vessel as Rogerk101 did as a last resort.
     
    The Teach likes this.
  5. The Teach

    The Teach Screwfix Select

    yes indeed,very good point.
     
    Heat likes this.
  6. rogerk101

    rogerk101 Screwfix Select

    Interesting ... I installed mine 28 years ago, and have never recharged it! :eek:
     
    Heat likes this.
  7. Heat

    Heat Screwfix Select

    Most likely just turned into a vessel full of water then, about 25yrs ago. :)
    Any of the air charged expansion vessels will slowly lose their air charge - same as a car tyre does.
    The air escapes through the membrane inside the vessels I believe.
    The expansion vessels on heating systems boilers, those that are on unvented cylinders and the wee vessels on negative head shower pumps all need their air charge topped up regularily.

    Note, for anyone using an expansion vessel on any potable water system must only use a potable vessel.
    Potable vessels made of steel do not have the water in contact with the metal because the water side is inside a balloon membrane.
    (There are some vessels made of stainless steel though)

    Heating system vessels are different and have a middle flat diaphragm with air charge to one side and water charge to other, both of which are inside the steel shell
     
    Last edited: Sep 27, 2018
  8. rogerk101

    rogerk101 Screwfix Select

    Mine doesn't have a membrane at all, it's just a big steel balloon that sits right at the top of the system, and just acts as a cushion/pocket of air that is a whole lot more compressible than water.
     
  9. Heat

    Heat Screwfix Select

    How does it work?
    It would need to be made of a rustless material, like stainless steel if no membrane, or balloon membrane.
    There would be an absorbsion of the air slowly into the water I would have thought. But I am not sure.
     
  10. rogerk101

    rogerk101 Screwfix Select

    You're probably right ... it probably is stainless steel, or may even be brass on the inside, but it's painted on the outside.
    Even if a small amount of the air is absorbed into the water, the same amount of air must be 'evaporating' out of the new water and they balance each other out.
    Remember, this is mounted out of the water flow, on top of a 15mm pipe that is T'd off the main water pipe so there's not a big area for such an air:water exchange.
    It has nothing to do with pressure regulation, so doesn't need a balance between the air pressure and the water pressure (I already have a static water pressure regulator set to 3 bars).
    All this is doing is dampening any hydraulic shock caused by the rapid change of flow. [The electrical equivalent would be a capacitor used to eliminate voltage spikes, like the old condensors (capacitors) that we used to install in cars to stop electrical spikes like those from the spark plugs from being amplified by the car radio.]
     
  11. Heat

    Heat Screwfix Select

    Yes, I know the principle of what you have installed.
    One idea, often done years ago, was to tee off on the mains pipe into ball valve on cold water tank and fit a piece of 15mm copper dead leg vertical (usually about 150mm long) with a step end on it.
    It was intended as a shock absorber.
    I read the idea was flawed because the air in the pipe that would be compressed by the mains would slowly be absorbed by the water.
    Not really sure tbh.
    Are you sure your expansion vessel does not have an air valve on it?
    Just while on the subject of water hammer, I had one customer who got a new washing machine. It was mains only fill, so her hot supply was no longer needed, therefore no hose to be attached to hot w.m. valve.
    Although her hot water is from a gravity tank & cylinder system, the quarter turn taps then created a loud hammer when closed.
    All I can see it being was the removal of the hot supply hose to the previous w.m. Hose must have been acting like a shock absorber.
     
  12. The Teach

    The Teach Screwfix Select

    probably was not needed anyway ;)

    expansion vessels are a serviceable items,just add the item to your annual plumbing servicing schedule.

    vessels with nitrogen charge can be bi annually checked :)

    water hammer does not occur on correctly installed plumbing and associated plumbing products.Not all plumbing is diy ;)
     
    Heat likes this.
  13. rogerk101

    rogerk101 Screwfix Select

    I'm positive. There is no filling valve like a regular expansion vessel has.
     
  14. Heat

    Heat Screwfix Select

    I have never known of that type.
    Interesting and a simple design then
     
  15. Plumblyjumbly

    Plumblyjumbly New Member

    Dead legs in pipework can be the cause of water hammer. Worth investigating whether you have any dead legs in your plumbing, usually where an appliance has been removed and the pipes have been capped off with end stops leaving a dead end, or where there is a closed isolation valve that has not been 'bled' since the pipework was drained and refilled.
     

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