Cast Iron Radiator Valves - how do they work?

dbarck2000

My 1930s duplex has gravity hot water heat with cast iron radiators. Each radiator as a value on one side - down by the floor.

If I turn the value to fully closed (turned clockwise until it stops), the radiator puts out less heat but is never completely shut off. This is true with all the radiators on both the first and second floors.

I'm curious why this is. Would completely shutting of a radiator cause an imbalance in the system? Just curious...

Jamie Hall

Not a balance thing -- the valves were intended to never completely shut off to reduce, if not eliminate, the very real possibility of a cold radiator freezing.

JimP

There’s probably a small hole drilled in the valve. If the valves are old it’s possible they’re leaking for any number of reasons depending on the valve style.

guzzinerd

Jamie Hall said:

Not a balance thing -- the valves were intended to never completely shut off to reduce, if not eliminate, the very real possibility of a cold radiator freezing.

I thought the valves were there also to shut off/isolate the radiator in case of a problem.  No?  

I just repacked a valve on the leaky radiator so i could remove and patch it.  The valve is holding.

bburd

@guzzinerd hot water valves are different from steam valves. Hot water systems are at great risk of frozen and split radiators and pipes if a radiator is turned completely off in very cold weather. This risk does not exist in most steam systems.

guzzinerd

bburd said:

@guzzinerd hot water valves are different from steam valves. Hot water systems are at great risk of frozen and split radiators and pipes if a radiator is turned completely off in very cold weather. This risk does not exist in most steam systems.

Gotcha, thanks.  I missed the hydro part.

EdTheHeaterMan

I took apart a radiator valve once and found this configuration. The valve stem connected to a cylindrical inverted cup with one side cut away. When the valve was open, the cut away was facing the radiator, when you rotated the handle 180° the solid portion of the inverted cup covered the outlet to the radiator. There was a 1/8" hole in the solid side so when the valve was off, or closed there was a small amount of heated water entering the radiator.


There were other designs also, but this one piqued my interest and I asked some old timer why there was a hole in the “Closed” side? “So it don’t freeze” was his answer. "and you can't use that on steam"

reggi

The hole... This one has a 1912 patent I think from Ohio Brass ... .
The old-timer was right ..

hot_rod

guzzinerd said:

Jamie Hall said:

Not a balance thing -- the valves were intended to never completely shut off to reduce, if not eliminate, the very real possibility of a cold radiator freezing.

I thought the valves were there also to shut off/isolate the radiator in case of a problem.  No?  

I just repacked a valve on the leaky radiator so i could remove and patch it.  The valve is holding.




If that is a rubber washer on the bottom, it looks hardened and cracked, needs to be replaced to seal properly.

Hate to get chunks of that in the piping, pump and boiler.

It is not an ideal valve to balance with, but workable. The adjustment will be at the very bottom of the stroke.

mattmia2

guzzinerd said:

I thought the valves were there also to shut off/isolate the radiator in case of a problem.  No?

The valve can only stop the radiator from heating or balance it, it can't isolate the radiator because it is still connected to the return so it is still under system pressure (except in some limited older systems with 2 valves and some modern systems where 2 valves are more common).