This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
This type of radiator (see Fig. 3) is made up of wrought iron pipes screwed into a cast iron base. The pipes are either connected in pairs at the top by return bends or each separate tube has a thin metal diaphragm passing up the center nearly to the top. It is necessary that a loop be formed else a "dead end" would occur. This would become filled with air and prevent steam from entering, thus causing portions of the radiator to remain cold. For a given surface the average pipe radiator is more efficient than the cast iron sectional radiator.