Thermostatic Radiator Valves

Discussion in 'Plumbing and Central Heating' started by persont5, 19 Jan 2017.

  1. persont5

    persont5

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    Hi,

    Just a general educational question:

    When one turns the control knob on a TRV to a higher or lower setting, what is it connected to within the valve? I assume it's adjusting spring tension or something similar?
    (Assuming it's using a wax-based actuator.)

    Thanks in advance.
     
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  3. stem

    stem

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    Hi Persont5 and welcome to the forum.

    You've got the idea. As the room heats up, the thermal element expands and pushes a pin that in turn pushes the valve closed. As the room cools the thermal element contracts and a spring pushes the valve open.

    Turning the TRV control knob also raises and lowers the thermal element so that the temperature at which it starts to close the valve changes.

    Hope the diagram below helps.

    TRV.jpg
     
    Last edited: 19 Jan 2017
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  4. omega015

    omega015

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    Removed (stem beat me to it)
     
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  5. persont5

    persont5

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    Okay thanks for the responses and the warm welcome to the forum!

    On the diagram, is the spring in question the one between the two "0" ring seals, slightly above the valve disc?

    Edit: is the spring visible in the diagram? And if so where is it?
     
    Last edited: 19 Jan 2017
  6. Agile

    Agile

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    No, it is the one further up.

    But it does not have a specific contribution to the operation.

    Its purpose is to keep the wax element at the top and take up the movement as the head is turned.

    As Stem has said the control function is the up/down movement of the element pin relative to the water flow valve underneath.

    The lower spring in the valve is to push it's pin up to the normally open position. It is then pushed down to close it under the control of the wax element in the TRV head.

    They exert variable control so that under normal conditions the valve is passing a reduced flow which will maintain the room temperature at the set value.

    The cheaper wax element valves take about 45 minutes to respond but the more expensive liquid ones operate faster.

    Tony
     
    Last edited: 19 Jan 2017
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  8. persont5

    persont5

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    Okay, so the valve is kept open by the lower spring until the wax contracts or expands? At which point it opens further or starts to close respectively?

    So how exactly does raising or lowering the wax element effect the temperature at which the valve closes?
    Thank you for all the responses.
     
  9. stem

    stem

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    The spring keeps the valve open. If you were to remove the sensor head, the valve would be fully open. As the element expands as the room warms it pushes the valve closed.

    The element expands as the wax warms up. So, raising the element means that it will have to expand further to close the valve, and it won't do that until a higher temperature is reached.

    Lowering the head means that it will take less expansion, and so a lower temperature would close it.
     
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  10. SFK

    SFK

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    An okay video here showing TVRs:

    sfk
     
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  11. persont5

    persont5

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    Okay I understand now.

    Thank you all for your helpful responses and patience! :)
     
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