The boiler has a circulation pump that circulate the water
The reason you buy water for you iron, is that you do not want calcium and iron inside your iron, as these deposits will plug the holes in the iron. Similarly calcium and iron inside your radiator wil cause the holes to plug up and stop the flow inside your radiator. You can buy demineralized water or use the old way of clean rain water.
In the case of a cast iron radiator, you would vary the flow of steam or hot water to it by throttling the valve that feeds it. In the case of a "convector", you would vary the quantity of air that passes over the coil by adjusting the air shutter. lc
A column radiator is used to describe a typical cast iron radiator. The term describes the vertical columns that make up the radiator. The radiators can also be made out of steal and not cast iron. The steal is welded together.
A household radiator is cast iron. An automotive radiator would be aluminum or copper.
There are several companies who produce or sell cast iron models of radiators. For example, try the company 'Cast Rads' of the 'Radiator Center' for these radiators.
Normally if there are no roots water Jetting restores full flow by scouring the lines to like new condition
Answer There might be air trapped in the radiator, try bleeding. It's usually a flow problem. If the valves on all of the radiators are wide open, the steam will flow through the path of least resistance, often leaving some of the radiators lacking for heat. Try turning down the flow on some of the hotter radiators. You will need to spend a little time adjusting the flow... assuming that you have flow adjusting valves on the radiators. These old cast iron radiators have sections that are bolted together. Each section has a gasket to keep the steam or hot water INSIDE the radiator. Of course these old radiators collect rust over the years unless you are very careful and scientific about your water chemistry (most folks are not). You probably have a plugged hole in one of the gaskets between the section of the radiator that is getting hot and the section that is not getting hot. This "cold" section is being bypassed and not receiving any flow.
1/2" - 2" depending on demand
because it is designed in such a way for the ship to float on water
from the hub to the spigot
Buy a shorter one. Welding Cast Iron is a pain and to do what you want would require cutting out a section and re-welding the whole thing. Baseboard hydraunic heaters can be shortened but cast is a no go.
To clean cast iron use hot water and a cloth or sponge. Dry the cast iron right away. You should not use soap, and you should never soak cast iron or it will rust.