Wide Bore Radiator Valves with 15mm both sides

Discussion in 'Plumbers' Talk' started by Jimbo, Jun 29, 2020.

  1. Jimbo

    Jimbo Screwfix Select

    Looking for rad valve set with unrestricted bore for a large, end-of-circuit radiator.

    Currently using Drayton RT212. TRV has approx 6mm bore. Anything compatible (15mm compression both sides) with a larger bore?
  2. sam spade

    sam spade Active Member

    What makes you think that you need a valve with a bore greater than 6mm?
  3. Jimbo

    Jimbo Screwfix Select

    Maybe I don't. It's a long single-panel radiator and it has much more drop across it that the others.

    Some of the other radiators have the lock shields very almost closed so on the face of it not much more balancing that could be done, that said I just discovered that the TRV head can also be adjusted. Maybe I will try that.

    Radiator demand is about 70 litres per hour, existing valves are adding about 8mBar at each end according to the data sheet. Pipe circuit loss there I think is about 25mBar. So wider valves would surely help?
  4. sam spade

    sam spade Active Member

    A flow rate of 70 lph means an 800W or 1600W rad, depending on the temperature drop, which isn't exactly large. If the temp drop is very high (how high?) the flow rate needs to increase, which means you need a bigger pressure differential across the rad (essentialy between the flow Tee and the return Tee (assuming a bog standard twin pipe system).

    The fact that many rads have their lockshields almost closed (how far open - turns?) suggests that the pump may be on too high a speed. Do you have a separate pump? If not, which boiler do you have (make and exact model?

    What adjustment on the TRV head are you talking about?
    Jimbo likes this.
  5. The Teach

    The Teach Screwfix Select

    Honeywell VT117 has a decent size valve seat opening,think they are around 10mm ish. Well they were a few years ago.

    Tbh,correct pipe sizing is more important. :)
    Jimbo likes this.
  6. Jimbo

    Jimbo Screwfix Select

    @The Teach thank you - will pick one up! Agree, I can't change the diameter really but I am eliminating nuckle bends on the way to this part where I can. I think it will all help.

    @sam spade Thank you. Radiator is 2600x600 type 11, design is indeed 1600W with dT 20 (flow temp is 65*C, oil fired and hopefully heat pump in future). The drop across it is maybe 30+ *C when all radiators are open, as the TRVs elsewhere close this does improve. The radiator does get nice and hot at the top. TRVs are generally Drayton Wiser electronics.

    Most the valves are Drayton TRV4 or RT212 with their supplied lockshields (e.g. these). I have some Reina valves which have wider internals but have different spacing as are flat faced and couple against a rubber washer on the radiator side, rather than 15mm compression.

    Pump is UPS3, PP mode 2.

    Smaller radiators closest to the pump have lock-shields literally half or one turn on. However I have not adjusted the TRV head (yet - will get the key to do so).

    I am current re-piping the downstairs (radiator in question is on this section) and whilst the old pipes are end-of-life, I have found no evidence of any sludge or blockage in any of them.
  7. sam spade

    sam spade Active Member

    Half to one turn open is nothing to worry about. I suggest you rebalance the whole system. Here's how to do it:

    1. Remove all TRV heads and set all wheel valves fully open.
    2. Set the pump to fixed speed 2.
    3. Set all lockshield valves to ⅓ turn open (Yes, you did read one-third turn open!).
    4. Turn boiler on and allow it to heat up (Set room stat to a high temperature so the boiler keeps running.
    5. Measure the drop across each rad (I assume you have a suitable thermometer) and make a note of it.
    6. If the mean drop is above 20C set the pump to speed 3; and vice versa.
    7. If necessary, recheck the temperature drop on all rads.
    8. Now make small adjustments to the lockshield valves (1/12th turn, i.e half the flat on a hexagon nut) to raise or lower the drop.
    9. Adjust one valve at a time and wait five minutes for the change to have effect.
    10. You may have to go round the system several times to get it as you want it.
    11. Aim for the same drop across each rad, not a specific temperature.
    12. Set the pump as required.
    Jimbo likes this.
  8. Jimbo

    Jimbo Screwfix Select

    Thank you for taking the time to assist Sam, once I've finished my pipe work I'll re-do all of this. No doubt it will end up being a super hot day in August, just when we want the heating on max!

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