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Thread: Evohome : valve position status on the HR92 vs evotouch

  1. #1
    Automated Home Sr Member
    Join Date
    Apr 2016
    Posts
    51

    Default Evohome : valve position status on the HR92 vs evotouch

    Hi there,

    Can someone please confirm to me what the valve position is supposed to show ?

    It looks like when the valve is completely opened, the HR92 menu shows "100", and "0" when it is completely closed ...
    But issue is when I look at the evotouch many, advanced settings -> system resume, it shows strange percentages openings :

    For one of the room :
    HR92 valve position is at 65, and shows 26% on the evotouch system resume
    HR92 valve position then passes at 56 (so closes) , and shows 20% on the evotouch system resume

    on another room, the position of the HR92 is at 100, and it shows 100% on the evotouch (so completely opened), which looks ok there.

    According me both the HR92 and the evotouch should show the same number on the screen, being the percentage right ?
    Any idea ?

  2. #2
    Automated Home Legend
    Join Date
    Sep 2014
    Location
    Scotland
    Posts
    1,844

    Default

    Valve position on the HR92 is simply a percentage of total pin travel. 0% means pushed hard down and 100% means lifted right up. Note that the actual position of the pin for a given percentage will differ depending on whether you have Stroke set to 0 or 1. Stroke being set to 1 will operate the pin over a wider range - it pushes down harder/further to close and opens up further as well. In effect an increased range of operation. This might be necessary depending on the mechanical characteristics of your valve bodies.

    Heat demand sent to the controller and displayed in the system summary page is not the same figure but follows a relationship which I graphed and posted in another thread a while ago. I can't seem to find the thread now to link for you but here is the image:



    Generally a valve body will not start flowing water until the indicated pin position is about 30% (the pin has to travel a bit for the rubber seal to un-compress) and will be nearly fully flowing at around 70% so the graph above makes sense. Below 30% you don't want to call for heat if no water can flow. Above 70% the valve is flowing fully so further increase in heat will be obtained by requesting a greater duty cycle from the boiler relay. This explains the change in slope as in the middle section the heat is controlled primarily by varying water flow and in the right hand section primarily by varying heat demand sent to the boiler.
    Last edited by DBMandrake; 29th October 2019 at 11:16 AM.

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