What is a lockshield valve?
The lockshield valve is the valve on a radiator that is usually covered with a plastic cap.
The term “lockshield” means that once adjusted, the valve is shielded with the plastic cap that prevents it being accidentally changed.
Removing the cap reveals the top of a spindle, which usually has two straight sides at the top to take an open-ended or adjustable spanner.
Spindles on some older radiators may have a square or half-moon shape. The spindle is turned with the spanner to adjust the flow of water through the radiator.
The lockshield valve needs to be adjusted when 'balancing' radiators in the various rooms.
If a radiator is takes too long to warm up, it needs more hot water flowing through it. If it gets hot quicker than others, then the flow through it needs restricting unless you want particular rooms to heat up faster than others.