large apartment building, two pipe hot water system couple radiators not circulating

Titan30

hi guys I'm having trouble with couple radiators separate risers. 20 story building each supply and return riser has a tee that does two radiators which are dual temp fan coils. i bleed the hell out of two they have isolation valves and bleeders on all units. This is a uncommon problem for the building so when i told the super its not getting circulation he says how come now after all these years? what would be the best way to handle this balancing valves or a second circulator. What is best way to confirm its a flow issue.

Thanks for any help

QasimMohmood

From what you saying I doubt it's a flow problem since the other apartments are not being effected by this issue you need to get the air out off the system also make sure you have enough boiler pressure and while you bleeding it you need the maintain proper boiler pressure also where is the boiler located and what type of pumps you have on that any one has worked on this make sure the pump isn't shutting down on overload do you have purge valves on there if yes then purge the lines both ways if you have bleeders then you need to the keep bleeding till you get that little bit off left in the line.

aircooled81

So, you bleed the hell out of them, you're talking about air right? is air entrainment a new issue for this system?
If it is, two quick ideas from where the air might come from....
auto airvent(s) are no longer working properly;
expansion or compression tank is putting air back into the system;
high point in the loop has auto airvent, high point is neative and drawing air back into the return loop, because the pres reducing valve setpoint is not maintaining positive pressure anymore;
recent loss of water has added make-up water to the loop, which carries air and gasses, pressure in loop is too high to boil the entrained air out of the water and your radiators are the point of low pressure. this is why they are seeing more of the air accumulation than the others.

balancing valves sound like a reach, as they weren't there before. when problems are new, I look for what has changed.
the best way to monitor flow is a circuit setter and a petes plug adapter. if you dont want to cut one in because one does not exsist then you can.....
btuh=gpmxdeltaTx500x1
find out the btuh of the radiator, solve for gpm. measure the temp of air entering the radiator, and the leaving to get your delta, multiply x 500 the density of water, and 1 is the specific heat of water. the one only gets changed if it's no longer water your moving, like glycol or something else.
that can be compared to other radiators too, but the manufacture has already done the math to tell you at what specific gpm the btuh will be.

good luck.

Titan30

I bleed the units with purge valves they have isolation valves on both sides and purge valves on both sides so i can shut return and purge or same with supply, no air straight water at first cold then gets piping hot pressure is adequate. I also removed coil blew it out with hose to make sure its not clogged.

Paul S_3

When you bleed the air through purge valves is the water coming out hot....like your moving water from one of the mains out the purge valve?....if your really confident in your purging then if theres no air then it aint a air problem...then i would look at all the basics.....then look into what has changed like aircooled81 said......is this a direct or reverse return 2 pipe system?.....if its direct return how is it piped compared to the other floors has someone added more piping causing less flow??....Paul S