HW rad converted to steam; only heating halfway across

hws

I'm working on a 100+ year old steam system. Runs at 0.5-1 psi, all cast iron rads, no steam traps of any kind anywhere, in a church.

I'm told that one of the rads on the system is heating only halfway. I look at it, and it is a HW rad being used for steam service. Not original to the building, installed about 4 years ago to replace the malfunctioning original (the rad itself was purchased used and is actually about 40-50 years old). The vent is on the top of the rad, not halfway up where a steam vent should be/usually is. The church caretaker tells me that it's been like this since it was installed, 4 years ago.

My theory: an older radiator, it might be full of sediment from its previous life as a hot water radiator. If I disconnected it from the system and blew it out with compressed air, maybe this would solve the problem. Have any of you done this before? If so, what pressure would be ideal for this task?

OR, maybe the vent is the cause? I mentioned that it is installed at the top of the heater, not the middle. I'm not entirely familiar with what an incorrectly located vent can do or not do.

Anybody have any input?

Steamhead

Move the vent

that rad will work fine with the vent in the proper place. 

hws

drill and tap

Steamhead, have you ever ever drilled and tapped a cast iron rad? Cast in my experience is brittle, don't want any unfortunate incidents. is there a technique to it.

I'll need to make a new hole in the heater to correctly place the vent

Steamhead

We do it all the time

usually there's a boss in the cast-iron for this purpose. Don't remember the drill size at the moment, but it's whatever you use for a 1/8" NPT tap. 

Hap_Hazzard

5/16"

or 8 mm, if you're into that kind of thing. :-)