Clearing an airlock in a macerator

Discussion in 'Plumbing and Central Heating' started by Rogeranerley, 2 May 2016.

  1. Rogeranerley

    Rogeranerley

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    Had to disconnect a no problem, well functioning sanilslim from the wc pan in order to properly seal the adjacent shower screen.

    On reconnection, I made the mistake of flushing to check for leads without first switching the macerator back on. I only realised this error when there was sudden load noise coming from the shower waste. However, the overfill alarm didn't activate. I quickly flushed the system and all seemed well.

    On further flushing, I noticed that about 5-10 seconds after the motor had stopped its short couple of pumping bursts a gurgling noise was coming from the machine lasting around another 10 seconds, suggesting a progressive intake of air.

    In addition, the wash basin feeding into the unit, which had been making no previous sound, now makes a gurgling noise which slowly converts to a slowing popping noise.

    It seems there's an air lock somewhere in the macerator., but how can I cure it?

    I've tried putting the shower hose pressure down through the waste in case the non return flap on that side of the unit has become misaligned, but this has made no difference.

    I should mention that the outflow from the macerator head immediately drops down through a 32mm pipe to the floor void on a 10 metre run to the 110mm stack, avoiding the need for an AAV separate to the unit.

    Grateful for any advice.
     
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  3. HERTS P&D

    HERTS P&D

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    ????????
     
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  4. bernardgreen

    bernardgreen

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    Would it sound if the power was switched OFF ? ( do Saniflows have a battery backed over fill alarm ? )

    If it over filled then could the water have got into the level sensing switches and shorted them. Sewage laden water is probably conductive enough to short out the switch terminals and thus the motor will be getting some power though the level in the tank has dropped to where the motor should stop. The power through the shorting water will not be enough for the motor to run properly and it may well then make gurgling noises.

    The blades in a macerator are very dangerous, ensure the power is switched OFF before doing anywork. If the motor starts unexpectedly injury is very likely.
     
    Last edited: 2 May 2016
  5. Rogeranerley

    Rogeranerley

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    Thanks Bernard

    The unit is working OK and doesn't have to work too hard as it only needs to lift the fill to its head before gravity takes over. As a result, the pump usually clears the flushed material in two or three short 3-4 second bursts. That's all still working OK. It's the delayed gurgling noise from the machine and the basin waste that has me concerned that something's not right as a result of my mistake.
     
  6. Rogeranerley

    Rogeranerley

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    Sorry, should have said that a battery-powered alarm to cover overfill can be fitted to all Saniflos. Batteries are changed annually.
     
  7. bernardgreen

    bernardgreen

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    That sounds like gravity is sucking the waste out of the tank. I am not sure that is a good idea. Looking at Saniflow data the level sensing is by pressure from depth of waste pressing on a membrane that operates a micro-switch. Gravity sucking would reduce the pressure in the tank and stop the motor. That could explain why it is two or three short bursts and not continous running until the waste has been pumped down to the "empty" level.

    I would be looking at fitting an air gap or air admittance valve to prevent gravity syphoning ( sucking ) waste out of the tank.
     
  8. Hugh Jaleak

    Hugh Jaleak

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    Quite where do you propose this air gap or AAV be fitted?
     
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  9. Wherever it gets fitted a photo of the resulting explosive discharge of foul water should be worth seeing!
     
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  11. bernardgreen

    bernardgreen

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    As per this
    sani air gap.jpg

    Effectively a soil stack pipe with the vent high enough to not allow sewer gas to enter the building. Or an AAV a foot or two above the end of the pipe from the Saniflow to avoid pumped sewage being blasted into the AAV. Arranging the end of the pipe to be pointing down the stack would ( should ) eliminate the risk of the AAV being contaminated ( and hence not closing )

    The vertical pipe to be larger diameter than the pipe from the Sanislim
     
  12. Hugh Jaleak

    Hugh Jaleak

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    Oh right. Good luck then. I certainly wouldn't want to be anywhere near when the Saniflo operates....
     
  13. Rogeranerley

    Rogeranerley

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    When first installed, I checked with Saniflo regarding the short pump bursts. They informed that my gravity based installation only required these pumping bursts. As there's been no change in this action, it suggests the micro switch is properly functioning. Also, the Sanislim model has an AAV inbuilt. It used to be a small pipe extension at the top but has now been replaced in my model by a low profile breather cap housing what looks to be a charcoal covered one way membrane.

    One thought I had was that the rush of water to the main stack might be creating a partial vacuum which becomes lost be air returning from the stack causing the gurgling.
     
  14. The way the Sanislim is operating is correct - short bursts in a gravity based system is OK. The AAV function is managed by the breather cap so no other vents required.

    The gurgling could be caused by the weight of water pulling the basin trap - cured by fitting an AAV trap to the basin.

    How long was the unit disconnected/out of use while you were doing the repair job to the shower screen?
     
  15. So you're suggesting that the Sanislim should 'fire' it's contents into an open pipe when it operates?!?
     
  16. bernardgreen

    bernardgreen

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    What I said was based on the experience of installing a Mono Mutrator whole house system and the need to prevent gravity sucking waste out of the tank. ( sewer and tank were almost as the same level )
     
  17. bernardgreen

    bernardgreen

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    Most pumped systems do when they discharge into a stack pipe. I have never seen sewage coming out of the top of a soil stack where a pumped system has been involved. That said where a pumped system discharges into a manhole ( inspection chamber ) whch has a lateral 100 mm pipe to the sewer some care has to be taken with the benching ( bottom of the chamber ) to reduce the amount of splashing that occurs.
     
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