can someone please explain to me how this valve works? this goes to my old Weil Mclain old hot water boiler return manifold. can someone also please link me to this valve's drawing or schematic, or a cutaway so i may know if it's even possible to overhaul these valves. from the front of the valve, it looks like inside the body of the valve is a bushing and inside the bushing is an hex/allen looking like a plug that the allen wrench goes into, only does quarter turn cw and ccw. does this control the water flow from wide open to shut off? just above this is an air bleed port. the back side has a hex plug that uses a 1/4" allan wrench. 1/2" copper tubing sweated to the top and the bottom looks like its braised on the bottom. my problem is that out of 16 registers, only 6 actually gets hot. i've bled all registers till its a stream of water coming out the bleed ports. also assuming that when i turn this valve fully cw that the flow is shut, i bled these ports on these valves till hot water from above(supply) starts getting hot. after bleeding them all, i turned all to full ccw. then the only way i know that the 6 that works has water flow is the valves and copper tubes associated to the ones that works get really hot, and the rest on this manifold stays cold. is it possible that the registers that doesn't work has clogged valves, these valves? help please!!!