1. The typical lockshield valve is full open at about 1 to 1½ turns from closed. As many LS valves can open over two turns from closed you will have to wind the LS valve in over a turn before it starts to have the slightest effect.
2. A quarter turn open is much closer to the required setting.
Don't forget that a 15mm pipe can carry about 6kW at a 11C differential, so if you are connecting a 1kW rad to 15mm pipe you need to reduce the flow rate to 1/6th of the open flow rate.
If the valves are well closed then the pump pressure will be higher.
A higher pump pressure will better send more flow through the highest resistance circuit.
In practice setting to just open 1/4 turn is very close to a reasonable setting and an installer could bit a boiler, commission it and then leave it working for a day or two and come back to do the final balancing having left a reasonably well working system.
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