The ball joints are not held together by bolts in the ordinary way because all parts of the hot-blast system become heated to a high temperature and flange bolts under those conditions would become practically unworkable; moreover, even if they worked, they would be extremely slow, while haste is a vital condition in changing tuyeres. The horizontal joint at the top of the penstock is held together by steel yokes suspended from lugs on a steel ring resting on the flange of the nozzle, but independent of it, so that it can be turned in any direction without difficulty. This ring is made into two halves, and bolted together in order to get it around the pipe above the flange, and the back or upper side of the flange is turned off, as is the base of the ring, so as to facilitate this turning when it is required. The steel yokes are provided at the bottom with keys which engage heavy lugs cast on the sides of the penstocks near the top. These keys can be operated quickly and easily with a hammer, and practically as well when hot as when cold.

The horizontal ball at the base of the blow pipe is held to a joint by a long bolt with a right-hand thread on one end and a left-hand on the other, one end of which pulls against a steel stake set in a socket in the hearth jacket, the other end pulls against a heavy lug cast on the bottom of the penstock. The bolt operates through a heavy coil spring set between washers so that contraction and expansion of the penstock and blow pipe due to changes in blast temperature will be automatically taken up, the pressure of the spring being sufficient to make a tight joint at the base of the blow pipe against the pressure of the blast. Brass nuts are used on the draw bolt so that rusting will not make them difficult to operate. The draw bolt is far enough away from the blow pipe not to become heated and so remains easy to operate.

In case of serious trouble with the furnace, it is sometimes desirable to be able to release the blow pipe from the tuyere instantly so that the slag can be flushed out through the latter. This can be done in the design shown by prying the inner brass nut over the upper end of the stake. Then if the keys in the links, which hold the upper joint, have been slacked, the penstock will swing back under the pressure of the blast and the blow pipe will fall out of itself, opening the tuyere completely.

The penstock is lined with circle brick 2 inches thick, made for the purpose, and fitted to place. The ball joints at the top and bottom of the penstock are made separate from the penstock proper and bolted to it so that in case they are scarred or warped in use, they can be taken off and be replaced with others. This should not occur except at long intervals, and therefore bolts are used to hold these in place. Incidentally it is very much easier to turn a ball joint on a loose flange like this than it would be if it were cast solid on a crooked casting like the penstock. This construction has the further advantage that the ball flanges hold the brick lining firmly in place. It will be noticed that the female ball joints have a very narrow bearing surface, and that this is protected from an accidental injury by being below the line of the end of the ball casting.