"Jo King" wrote in
:

what is the difference between a lock shield valve and a wheel head
valve on a C.H. radiator

Nothing at all, physically; the lockshield has a cover, not a knob, as it's
not an operational control, but is set by the Guild approved wizard in the
commissioning rite called balancing, and it must nevermore be touched by
unconsecrated hands.

The wheel valve changes the rad from ARF mode to ARN condition and vice
versa, and is fitted with a knob to enable muppets to do this without
danger

mike