Siamp WC cistern valve - how does the fill valve work?

Discussion in 'Plumbers' Talk' started by diymostthings, Jul 28, 2010.

  1. diymostthings

    diymostthings Well-Known Member

    The reason I ask is that our Siamp fill rate has become very slow. (i.e. over 3 minutes to fill the cistern) We have 3.6 bar pressure. Yes I know the rubber diaphragm gets a little tear in it and has to be replaced (£3.49 from B and Q)but in this case there is no tear and no debris in the valve. I've watched the thing filling up and I literally can't work out how the mechanism works! Lifting the float to try to shut off the water as it is filling doesn't stop the flow! But if you wait for it to reach its full level it does stop!!!

    Has anyone had this problem, cured it or can explain how it works? (the Siamp website has a good exploded diagram but still can't work it out).

    On a wider issue - how long should you normally wait for a WC cistern to fill?

    Thanks for any thoughts

  2. tackleburger

    tackleburger New Member

    Change it and fit a fluidmaster they sell them on here.
  3. tackleburger

    tackleburger New Member

    Item no. 84007
  4. Captain Leaky

    Captain Leaky New Member

  5. Captain Leaky

    Captain Leaky New Member

    Probably dirt in the stem of the valve.
  6. G Brown

    G Brown New Member

    You could get a plumber in ;)
  7. ThreadJacker

    ThreadJacker Active Member

    You need to lift the float and hold it there for a few seconds, it works on a different principle as a simple ballvalve. Something to do with air going through a tiny hole and building up pressure on the other side to operate the diaphram.

    Something like that.
  8. G Brown

    G Brown New Member

    Venturi ;)
  9. tackleburger

    tackleburger New Member

    Like i said fit a fluidmaster
  10. ThreadJacker

    ThreadJacker Active Member

    Has anyone had any problems with Fluidmasters making all sorts of funny noises?

    I've had a few recently, one sounded like a hair dryer when filling and one squeeked each time a HOT tap was turned on and off, not the cold though!
  11. diymostthings

    diymostthings Well-Known Member

    You could get a plumber in ;)

    I can plumb them in till the cows come home - but as has been ably demonstrated on here-plumbers don't know how they work! Hiding behind "venturi" says it all!
  12. G Brown

    G Brown New Member

    See the thing is daftydiymostthings - you have to make up your mind:

    Do you want to come on a TRADE forum and pick the finest TRADE brains to help you in your DIY?

    Or do you want to insult the very same TRADESMEN whose help you need?

    You can't have it both ways.

    Developing a GSOH and having your own hair and teeth is helpful too. :)
  13. diymostthings

    diymostthings Well-Known Member

    is helpful too. :)

    Yes you're quite right as usual CC. I really do appreciate the helpIi get from the experts here. Sorry I sounded grumpy as I had had a bad day.

    Kind regards and thanks to the other who responded

  14. Captain Leaky

    Captain Leaky New Member

    That's nice!

    A sincere apology! :)
  15. G Brown

    G Brown New Member

  16. Spyder

    Spyder New Member

    Well it is a bit of fluid dynamics, the way they work but I doubt that it's a venturi which is to do with pushing a gas or liquid through a choke and there being a resultant reduction in pressure in the medium in the choke area.

    The fill valves work as follows: there's a small hole in the diaphragm through which water flows under a slight pressure. There is a second hole in the body of the valve through which the water leaks into the cistern when open. This hole is closed off when the water gets to the required level. Now as a result of the hole in the body being closed, the water is pressurised behind the diaphragm. Now you would be forgiven for thinking that "so what, it's the same pressure on both sides of the diapragm so no net gain". However, because the water on the outlet side of the diaphragm is running out into an open cistern, there is a small but significant difference in pressure. So the pressure behind the diaphragm builds up and closes the diaphragm against the inlet jet. Simple isn't it? It takes time to operate because the water has to flow through the hole in the diaphragm and build up the pressure. Now there are different locations for the exhaust hole, but the mechanism is basically the same. That's why you fit a special diaphragm for low pressure installations and you can't use then with whole house pumps.
  17. Captain Leaky

    Captain Leaky New Member

    Properly known as "equilibrium" valves - the best known being Torbeck.
  18. diymostthings

    diymostthings Well-Known Member

    can't use then with whole house pumps.

    Thanks for that detailed explanation Spyder. The behavior I have noticed fits your description. I'll read it through carefully now with an exploded view of the valve and try to work it out.

  19. diymostthings

    diymostthings Well-Known Member

    known being Torbeck.

    Thanks Captain Leakey. I am familiar with the Torbeck valve which has a lot in common with the standard ball valve. The Siamp seems to have another level of complexity and relies on this "two hole" principle as expounded by Spyder. The Torbeck float seems to be just that - a float which rises and shuts off the valve. You can lift the float manually with the same effect. With the Siamp the float is an upside-down air reservoir which seems to delay the shut off even when the float is manually lifted. I'm determined to get to the bottom of it!

  20. Stuart Jnr

    Stuart Jnr New Member

    The Siamp 99B inlet valve works from 0.2bar of pressure - 20 bar of pressure. It is completely WRAS approved and is the most common inlet valve sold in the UK market.
    Can i ask, your toilet is on a mains feed? Its not from a gravity fed tank is it?

    It could well be that you have a faulty inlet valve. If you send a copy of your recipt to Siamps office in Manchester they will send you out a replacement f.o.c.

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