Setting up a balancing valve on a cylinder coil on Y plan?

[Ric2013]

Whether it be the usual gate valve or the more correct lockshield valve.

Jennie raised a point elsewhere on this forum and someone mentioned the purpose of these being 'by reducing the flow, the coil will remain hotter longer. Thus heating the water quicker'.

Makes no sense to me as reducing the flow would surely reduce the average temperature of the coil. I'd have thought the maximum heat transfer would happen when the average temperature of the coil was as high as possible, hence better to leave the valve fully. Great on a W plan.

But on a Y plan, that would rob flow from radiators and unbalance the system, so I'd aim at having the same temperature drop across the coil (with the cylinder cold) as across each radiator. As the cylinder heats up, the temperature drop across the coil will reduce to very little, but you need a high coil temperature to get the secondary water to 60°C without excessive boiler cycling, so I suspect the setting should be carried out with a cold cylinder.

But this is just my opinion. Any thoughts?

 

[Aire]

I always thought the only reason for them was to restrict flow through the cylinder to allow more flow through the radiators. Never considered it an option of keeping heat in the coil because as you say, that makes no sense.

 

[fixitflav]

But on a Y plan, that would rob flow from radiators and unbalance the system

Agreed, I've never seen much advantage in a mid-position valve, as if the cylinder only is heating, and then CH calls, there is cold water through the coil for a while and cylinder temperature likely to fall. Maybe not recover till CH is satisfied, specially if the rads are generously sized to help condensing. Throttling the coil flow might help, but as you say, that would reduce the heat transfer when HW only is calling.