Operation of Air Vents

abellia

Can someone please explain how air vents in a steam system actually work and how the adjustable vents are different from the non-adjustable ones?

KC_Jones

Check out this video by our very own @Gordo

https://www.youtube.com/watch?v=LeYDZvD7NmI

The adjustable vents just varies the size of the opening to vary the rate it releases air.

abellia

Sorry, I don't understand. So as they heat, they close? So when steam hits them, they'll start to close until they heat to some limit? Are you guaranteed to get all the air out before they close or will the air itself heat because it's compressed as the valve closes? Does steam escape at some point before the valve closes all the way?

KC_Jones

They close when steam hits them, if the steam hits them basically all the air is gone so there is nothing for them to do. In the presence of steam they pretty much close instantly, some brands will even have an audible click when closing.

You don't ever want steam coming out of them, if it is you have a problem.

JUGHNE

Most (not all) air vents also have a float that will rise and close the small vent hole. This is in the event that enough water somehow gets into the vent body.

abellia

So the adjustment (or sizing of the valve) allows for steam to hit all the radiators, essentially, at the same time. Those valves that are slower keep air in the system for a bit until steam can reach the farthest points. Am I understanding?

KC_Jones

For venting you want to approach as if you have 2 systems, the first is distribution which are the mains and the second is actual heating which is the radiators.

You want to vent the mains as quickly as possible to get steam to all the radiators at about the same time. Once the main vents close the rad vents take over.

For the radiator vents you want them to go slowly to allow for some control, but you want them to be sized for the work they are trying to do in that room. This can be a combination of run out length to radiator valve, radiator size and location in the house. A hot room you might go smaller a cold room you might go bigger.

For example the smallest radiator in my house has the biggest vent because it's got a long run out and I need to maximize it's output all the time due to it being on the smallish size compared to the load.